or Ca²⁺) associated with other pigments/components of the paint that can act as counterion forming lead arsenates or calcium arsenates (reaction F). Whether As⁵⁺ species can form directly from As₂O₃(s) (reaction D), or it needs to be dissolved first (reaction D, then E), needs to be studied further. The mobility of arsenates can explain why such compounds were often encountered widespread across the paint stratigraphy (cf. Figure 23f).

Black Cu-, Pb- and Ag-sulfides were identified by SR µ-XRD in a series of paint mock-ups and thirteenth–fourteenth century Italian tempera paintings, in which either Cu-/Pb-containing pigments (e.g., verdigris, red lead) or metallic silver were found either in mixture or in close contact with orpiment [46, 71, 72]. The formation of reactive sulfur species (e.g., polysulfides, S-radicals, and H₂S) arising from the degradation of arsenic sulfide paint was exploited to explain the formation of such compounds.

Further systematic research on paint mock-ups is ongoing to understand how other local conditions (e.g., pH, nature of the binding medium, and matrix composition) must have an influence on the complex degradation pathways of arsenic sulfide pigments.

## 6.5 Red mercury sulfide pigments

### 6.5.1 Discoloration issues

Red α-HgS, used as a pigment both in its natural and synthetic forms, has received multiple denominations across different historical periods. Since 1962, according to the US Department of Standards, the naturally occurring pigment is called cinnabar, whereas the term vermilion is applied to the artificially prepared pigment [6]. The application of the mineral ore of cinnabar as a pigment is attested since at least the sixth century BCE in Greece, Asia Minor, and Egypt, among other territories [499, 500]. Despite its attractive red color, this pigment suffers from discoloration, and its appearance ranges from whitish, gray or purple to black.

Its discoloration has been noted since Antiquity [1, 501] and its results can be observed in many Roman mural paintings [502, 503]. Medieval case studies in which α-HgS has discolored are the plasterworks of the Hall of the Kings of the Alhambra (Granada) and the mural paintings of the Gothic church of the Monastery of Pedralbes (Barcelona) [12, 382, 504]. Regarding easel paintings, darkened vermilion has been observed in several fourteenth–seventeenth century artworks from the National Gallery of London and the Courtauld Gallery [10]. The examples range from egg tempera to oil paintings (either on panel or canvas), such are those by Nardo di Cione (ca.1365), Paolo Uccello (1450–1460), and Jacob Jordaens (1620–1625). Discolored vermilion was also noticed in a tempera work by Francescuccio di Cecco Ghisi (1375, North Carolina Museum of Art) [505] and in the following oil paintings: *Triptych of Saint Wilgefortis* by Hieronymus Bosch (ca.1497, Gallerie dell'Accademia di Venezia, Italy) [506], *Minerva and Hercules Opening the Doors for Victory* by Christiaan van Couwenberg (1651, Oranjezaal Huis ten Bosch Palace, The Hague, The Netherlands) [11], *Portrait of a Lady* (ca. 1625, Mauritshuis, The Hague) [11], and *The Adoration of the Magi* (1624–1625 Royal Museum of Fine Arts of Antwerp, Belgium) [12] both by Peter Paul Rubens.
## 6.5.2 Chemical analyses of degraded α-HgS

*Historical paintings.* Over the years, there has been a plethora of different hypotheses trying to disclose the nature of discoloration of α-HgS. As summarized in Table 3, several laboratory and SR-based techniques have been used (being with X-rays or not) to detect the main degradation compounds associated to the transformation of this pigment.

Until the twenty-first century, many researchers associated the darkening of red α-HgS to the formation of black metacinnabar (β-HgS). This was proved by Istudor et al. [507] by XRD investigations of mural paintings of a northern Moldavian church. β-HgS was also detected via pump-probe microscopy in a fourteenth century tempera painting attributed to Francescuccio di Cecco Ghissi [505].

Besides metacinnabar, many other degradation products were identified in altered α-HgS painted areas. Spring et al. [10] were among the first to point out the possible key-role played by chlorine in the degradation of α-HgS. Notably, the study of cross-sections from fourteenth to seventeenth century artworks, via a combination of SEM-EDS and Raman spectroscopy, revealed the presence of chloride in the outer, deteriorated dirt crust of the paint stratigraphy, in some cases associated with the

<table><caption>**Table 3** Degradation compounds found on degraded α-HgS paintings/samples and analytical techniques used for their detection</caption><thead><tr><th>Compound</th><th>Color</th><th>Analytical techniques</th></tr></thead><tbody><tr><td>β-HgS</td><td>Black</td><td>XRD [507, 508], pump-probe microscopy [505, 508]</td></tr><tr><td>Amorphous phase</td><td>Black</td><td>XRD [509, 510]</td></tr><tr><td>Hg(0)</td><td>Black</td><td>SEM-EDS [11], linear sweep voltammetry [511], XPS [512], FESEM [513], pump-probe microscopy [505, 508]</td></tr><tr><td>Hg<sub>2</sub>Cl<sub>2</sub></td><td>White</td><td>Raman spectroscopy [8, 10], TOF-SIMS [506], XRD [517], μ-XRD/SR μ-XRD [12, 146, 234]</td></tr><tr><td>HgCl<sub>2</sub></td><td>White</td><td>SIMS [11]</td></tr><tr><td>α-Hg<sub>3</sub>S<sub>2</sub>Cl<sub>2</sub></td><td>Purplish-gray [12], light orange–pink (turns grayish black when exposed to light) [146], yellow [234]</td><td>μ-XRD/SR μ-XRD [12, 146, 234]</td></tr><tr><td>γ-Hg<sub>3</sub>S<sub>2</sub>Cl<sub>2</sub></td><td>Yellow (turns grayish black when exposed to light) [12]</td><td>SR μ-XRD [12, 234]</td></tr><tr><td>β-Hg<sub>3</sub>S<sub>2</sub>Cl<sub>2</sub></td><td>Yellow [515]</td><td>SR-μ-XRD [234]</td></tr><tr><td>HgSO<sub>4</sub>·H<sub>2</sub>O</td><td>White</td><td>XRD [513]</td></tr><tr><td>Hg<sub>3</sub>(SO<sub>4</sub>)O<sub>2</sub></td><td>Yellow</td><td>XRD [513]</td></tr><tr><td>CaSO<sub>4</sub>·2H<sub>2</sub>O</td><td>White, but detected in black layers</td><td>μ-XANES at the S K-edge [7, 12, 382], Raman spectroscopy [8]</td></tr></tbody></table>
presence of white calomel (Hg₂Cl₂). The latter compound, which does not explain the grayish aspect of degraded α-HgS painted areas, was suggested to be present along with sulfur and black undetected forms of HgS, such as either metacinnabar or an amorphous phase. The combination of α-HgS with other pigments, including red lead, was also suggested to preclude the formation of sulfochlorides, such as corderoite (α-Hg₃S₂Cl₂) (a potential precursor of calomel) [10, 510].

Few years later, other authors [7, 8, 11, 12, 516] have also reported the influence of chlorine (even at trace levels) in the darkening of cinnabar, especially in humid areas and/or with direct sunlight exposure. Keune et al. [11] demonstrated that chloride ions, identified as mercuric chloride (HgCl₂) in the analyzed samples by SIMS and EDX, even if present in small quantities in the native pigment, may catalyze a photo-electrochemical process in which cinnabar decomposes in gray metallic mercury (nanoparticles) and sulfur (possibly volatilized via oxidation to sulfur oxide). In this case, neither calomel nor metacinnabar was identified.

The study of Cotte et al. [7] of blackened samples from Roman wall paintings of the Vesuvian area (Fig. 25a) was pioneering in demonstrating the usefulness of SR-based X-ray techniques to characterize the degradation state of α-HgS. SR µ-XRF mapping and S/Cl K-edges µ-XANES measurements allowed the local chemical speciation of S- and Cl-bearing degradation products of cinnabar to be determined in gray and black areas. µ-XANES spectra acquired at the Cl K-edge on gray degraded areas were very similar to a series of mercury chloride compounds [i.e., corderoite, calomel, and terlinguaite (Hg₂OCl)] and at the S K-edge to that of corderoite. In the black Pompeian degraded samples, S K-edge µ-XANES spectroscopy revealed also the presence of high amount of sulfates, with spectra similar to that of gypsum (Fig. 25b). In S K-edge XANES spectra, the position of the white line shifts toward higher energies with increasing oxidation number of sulfur (i.e., sulfides, E₁: 2.471 keV; sulfate, E₂:

<figure><img src="image_38.png" /><figcaption>**Fig. 25 a** Blackened cinnabar on a wall painting (“Villa Sora” in Torre del Greco, near Pompeii, Italy). **b** S K-edge µ-XANES spectra acquired on a black area: fit (orange) of the experimental data (black) by combination of cinnabar (red) and gypsum (green) spectra. **c** Cross-section of a sample of a blackened cinnabar wall painting. The dotted rectangle indicates the area analyzed by µ-XRF/µ-XANES. **d** RG SR µ-XRF maps of S²⁻/S⁶⁺ species (data collected at ESRF-ID21; photo credits: Mario Pagano, Soprintendenza per i Beni Archeologici del Molise). Adapted with permission from [7]</figcaption></figure>
2.482 keV). As explained in Sect. 2, this property can be exploited to semi-qualitatively map sulfides and sulfates, by recording the same µ-XRF map at the two corresponding energies over the paint cross-section (Fig. 25c,d). The result shows that sulfates form a continuous blackened layer of about 5 µm at the surface of an intact sulfide paint.

Later, Radepont et al. [12] illustrated the necessity of integrating SR µ-XRD with SR µ-XRF/µ-XANES to more specifically characterize the chemical nature of crystalline secondary compounds and to visualize their distribution across the paint stratigraphy. Notably, the study of original painting samples taken from different art-works, including the Gothic wall paintings of the Monastery of Pedralbes in Spain (Fig. 26a,b) identified, besides to the presence of calomel and corderoite, two rare and relatively unknown polymorph phases: γ-Hg₃S₂Cl₂ (kenhsuite) and β-Hg₃S₂Cl [12, 234]. SR µ-XRD maps (Fig. 26c,d) revealed that the β-form, present as a relatively thick layer (~ 20 µm) in close contact to α-HgS, is covered by a thinner layer made up of γ- and α- forms (~ 2–5 µm) and of an uppermost layer of Hg₂Cl₂. Such distribu-tion suggests a progressing conversion of one phase into another, until the complete substitution of sulfides by chlorides [234].

More recently, Pérez-Diez et al. resumed the study of cinnabar-decorated mural paintings from the Vesuvian area [8, 516] by combining in situ studies of blackened paintings using portable instruments and the investigation of affected samples in the

<figure><img src="image_39.png" /><figcaption>**Fig. 26** a Darkened cinnabar on the wall paintings of the Monastery of Pedralbes (Photo credits: Javier Chillida, Chillida Conservación-Restauración Art S.L.U.). The white arrow points to the area in which a sample was taken. b Cross-section of a degraded sample taken in a gray region. SR µ-XRD maps of cinnabar and four Hg degradation compounds: c composite map and d distributions of each crystalline phase (data collected at P06-PETRA III, DESY). Adapted with permission from [234]</figcaption></figure>
laboratory. SEM-EDS, micro-Raman spectroscopy, and XRD measurements allowed the possible presence of mercury perchlorate hemihydrate $[Hg(ClO_4)_2 \cdot 2H_2O]$ along with calomel and gypsum to be identified. In near future, SR µ-XRD mapping analysis will be performed to assess the presence of additional Hg-S, Hg-Cl, or Hg-S-Cl degradation compounds.

*Paint mock-ups.* In addition to the study of historical paintings, many experiments have been carried out on paint mock-ups. A series of studies have evaluated the effect of light on α-HgS degradation [19, 28, 517]. Elert et al. [512] used XRD to investigate outdoor exposed cinnabar-based mock-ups, but without observing any changes, possibly due to the formation of black amorphous metallic mercury. In a subsequent study by the same authors [513], XRD and XPS investigations of cinnabar pigments and tempera mock-ups attributed the blackening due to UV-C light exposure to the oxidation of HgS to mercury sulfates [i.e., $HgSO_4 \cdot H_2O$ and $Hg_3(SO_4)_2O_2$] and their reduction to Hg(0) by photo-induced electron transfer. The sensitivity of pump-probe microscopy to distinguish among α-HgS, β-HgS, and metallic mercury was also recently exploited for studying UV-degraded samples, revealing the formation of both metallic mercury and β-HgS [505, 508].

Further experiments and calculations have been dedicated to assessing the formation of metacinnabar under the effect of temperature. Ballirano et al. [333] evaluated the possibility of the thermal transformation of cinnabar to metacinnabar in Pompeian wall paintings and its persistence over a span of 2 millennia, attributing this to the reported slow kinetics of transformation [518, 519]. More recently, thermodiffractometric experiments in an open system have excluded the possibility that metacinnabar can be formed in cinnabar-decorated fresco paintings because of the thermal impact that took place in Pompeii due to the 79 CE eruption [509]. However, thermal experiments in a closed system allowed the formation of metacinnabar to be detected.

Studies aimed at tracking the combined effect of light and chlorides on the degradation of α-HgS have also been performed over the last two decades. Neiman et al. [514] infused cinnabar fresco mock-ups with NaCl and exposed them to sunlight, next to powdered pigments affected by 5 M NaCl solutions and they studied the aged samples using XRF, SEM-EDS, and XRD. Including also in their methodology thermodynamic modeling, the authors concluded that both chlorides and light were fundamental to induce discoloration, although calomel could already occur in the absence of light.

Radepont et al. [146] reproduced the alteration process of α-HgS by preparing synthetic pellets of the pigment and by exposing them to Cl-solutions and ClO(g) either under UV-VIS radiation or in the dark. SR µ-XRF, µ-XANES, and µ-XRD were crucial to detect calomel, corderoite, and sulfates from the reaction of α-HgS with ClO(g) formed from the exposure to light and NaOCl solution. The distribution of layers of mercury chloride compounds atop red mercury sulfide layers, and sulfates present at the surface, mimic the one observed in historical paintings, as shown in Fig. 26 [12]. In the case of a two-layered pellet composed of $CaSO_4 \cdot 2H_2O/α-HgS$ aged with NaOCl solution, the formation of $Hg_2SO_4$ was also observed.

In summary, the degradation of red α-HgS is a very complex phenomenon where light, temperature, humidity, and external agents, such as chloride species, can play a role. These parameters can act separately or combined and lead to the formation of various species, including metacinnabar, metallic mercury, different sulfates (mercury
sulfates but also gypsum when a source of calcium is available), and a series of Hg–S–Cl and Hg–Cl compounds.

From the analytical point of view, the combined use of SR-based XRF, XRD, and XANES techniques was found to be particularly efficient for gaining complementary information on the nature and stratigraphic distribution of most of secondary compounds in both degraded mock-ups and historical samples. The development of HERFD-XAS seems extremely promising to further study Hg speciation (through Hg L₃-edge µ-XANES), in particular to detect the presence of Hg(0).

## 6.6 Cadmium sulfide-based pigments

### 6.6.1 Properties and alteration phenomena

Cadmium yellows and reds are II–VI semiconductor materials based on cadmium sulfide (CdS), which have found extensive use among artists of mid-nineteenth–twentieth century because of their vibrant colors and excellent tinting and covering power [520].

Different dry and wet synthetic routes were developed to achieve various pigment hues by modifying the crystal morphology (i.e., grain shape and size) and the optical and optoelectronic properties [i.e., hue, band-gap energy (Eg)] of these classes of pigments [521–523]. A wide range of materials, with shades spanning from the lemon-yellow to the purple-red ones corresponding to Eg values between ~2.65 eV (~470 nm) and ~1.95 eV (~635 nm), were synthesized by introducing variable quantities of either zinc or selenium into the structure of CdS as solid solutions described by the formula Cd₁-xZnxS and CdS₁-xSex. Yellow-orange and orange hues were obtained, instead, by changing the crystalline structure of CdS from the hexagonal (Eg: 2.44 eV/508 nm) to the cubic one (Eg: 2.36 eV/525 nm) [524, 525].

As direct semiconductors, Cd₁-xZnxS and CdS₁-xSex solid solutions exhibit direct radiative recombination with green-orange emissions in the 490–630 nm range (known as near band edge emission, NBE) and radiative deactivation from intragap trapping states due to crystal defects, which give rise to peculiar red and near infrared emissions in the 680–1110 nm range (known as deep level emissions, DLEs). The positions of the NBE and DLE maxima and that of the inflection point of the visible diffuse reflectance spectra depend on the zinc and selenium content of Cd₁-xZnxS and CdS₁-xSex as well as on the grain sizes of the pigment, when these are in the nanometric scale range. Therefore, photoluminescence and VIS–NIR reflectance spectroscopy have been profitably used for the non-invasive characterization of different cadmium yellow and red formulations in paintings and historical pigments [149, 526–531].

X-ray methods, namely XRD (employing SR and traditional sources) and SR µ-XANES at the S K-/Cd L₃-edges, and SR deep-UV excited micro-photoluminescence allowed researchers to successfully study some of the causes of the discoloration phenomenon observed in a series of late nineteenth–early twentieth century masterpieces (Fig. 27). These methods provided insights down to the submicrometric scale length and were also applied to artificially aged paint mock-ups [34, 36, 87, 97, 101, 102, 124, 125, 135, 532].
<figure><img src="image_40.png" /><figcaption>**Fig. 27 a** Photograph of *The Scream* (ca. 1910) by Edvard Munch (MUNCH collection, Oslo, catalog nr. Woll.M.896) showing the altered cadmium yellow areas (Photo credits: Irina Crina Anca Sandu and Eva Storevik Tveit, MUNCH collection) along with the micrograph of the micro-flakes sampled from the flaked-off yellow area of the lake and analyzed by µ-XRD and µ-XANES. Adapted from [102]. **b** Photographs of an untitled painting by Joan Miró (1977, Fundació Miró Mallorca, Spain, catalog nr. FPJM 00135), with close-up pictures of the cadmium yellow passage under VIS and UV light showing the pink/orange luminescence emitted by the altered cadmium yellow paint. Adapted from [135]</figcaption></figure>

These studies have established that, under high moisture conditions and illumination with supra-band-gap light ($h\nu > E_g$), the CdS pigment undergoes oxidation of sulfides ($S^{2-}$) to white cadmium sulfates ($CdSO_4/CdSO_4 \cdot H_2O$). The process is related to the chemical composition, morphology, and degree of crystallinity of cadmium yellow, all properties depending on the manufacturing process of the pigment itself. Notably, $Cd_{1-x}Zn_xS$ solid solutions [125, 532] and nanocrystalline and/or poorly crystalline CdS [87, 135] exhibit the highest sensitivity toward photo-corrosion. The in situ $S^{2-} \rightarrow S^{6+}$ oxidation may take place also in the dark by exposing the paint to high moisture conditions and in the presence of chloride species, which are often residues of the starting reagents of certain CdS formulation synthesized by wet processes [102, 124, 521]. Exposure to humidity can also trigger secondary reactions that occur via dissolution, migration, and recrystallization of water-soluble/-partial soluble phases [such as $Na_2SO_4$, Cd(OH)Cl, and magnesium carbonates], thus favoring the formation of further $CdSO_4$, sodium/cadmium chlorides, and/or hydrated magnesium sulfate by ion exchange [102, 533].

Additional secondary products, resulting from the oxidative degradation of the oily binder or its interaction with $Cd_{1-x}Zn_xS/CdS$ (i.e., cadmium oxalate, zinc oxalate, and long-chain fatty acids), were also revealed by TOF-SIMS imaging [534] and mid-FT-IR spectroscopy (with both SR and traditional sources) [98, 101, 125]. Pump-probe measurements allowed the achievement of information about the early stage detection of CdS degradation on the micrometer scale, that mainly affects small particles and the surface of larger particles [535], and the formation of a defective phase, compatible
with Cd vacancies and the formation of both CdO and CdSO₄ superficial clusters [536]. The interpretation of most of these experimental data is consistent with ab initio simulations on the subject [124, 537–539].

Alteration phenomena of cadmium red paints have been less frequently investi-
gated to date. Rayner et al. [540] observed the discoloration of orangish CdS₁⁻ₓSeₓ
in an ancient Greek terracotta krater (ca. 430–420 BCE), where the paint was applied
for restoration purpose. The application of SEM–EDS, pyrolysis-GC–MS, XRF, and
vibrational spectroscopy investigations of the retouched areas of the krater, combined
with the study of treated terracotta mock-ups, led authors to conclude that light and
chlorine species were two key factors prompting the fading of the orange paint. In addi-
tion, the possible formation of a series of alteration products, including selenium-rich
compounds as well as cadmium sulfate, cadmium oxalate, and/or cadmium carbonate,
was suggested. The alteration of CdS₁⁻ₓSeₓ has been also identified in a selection
of twentieth century artworks by Monico et al. [149]. XRD, VIS–NIR, and FT-IR
spectroscopy investigations of paintings and of a set of CdS₁⁻ₓSeₓ paint mock-ups
established that, under the exposure to light and moisture, the alteration is due to the
oxidation of original sulfides to white cadmium sulfates and is favored for the pigments
containing the lowest amount of Se.

In what follows, a selection of cadmium yellow degradation studies published
during the past decade on early twentieth century masterpieces by Edvard Munch,
Pablo Picasso, and Joan Miró and related artificially aged paint mock-ups will be
detailed. They will highlight how SR-based X-ray methods and SR deep-UV excited
micro-photoluminescence significantly contributed to unveil the nature of secondary
compounds in altered cadmium yellow paints at the (sub)micrometric-scale length and
to inform on some of key factors prompting the overall degradation process.

6.6.2 Moisture and chlorides as key factors for the alteration

The version of *The Scream* (ca. 1910), belonging to the MUNCH Collection in Oslo (Norway), displays clear signs of discoloration of cadmium yellow brushstrokes of the sunset cloudy sky and the neck area of the central figure, while flaking and paint loss are visible in the lake water, where a thick cadmium yellow paint was applied (Fig. 27a).

SR-based X-ray methods, namely µ-XRD, µ-XRF, and µ-XANES spectroscopy at the S K-, Cl K- and Cd L₃-edges were performed on minute flakes taken off from the surface of the yellow lake to obtain speciation information on the S, Cd, and Cl compounds present [102, 124]. SR µ-XRD and S oxidation state maps (Fig. 28a,b) reveal that poorly crystalline hexagonal CdS and CdCO₃ are the main components of the yellow paint, with sulfate compounds present as micrometric agglomerates (with diameter of ~ 3 to 12 µm). As shown by S K-edge µ-XANES spectroscopy measurements (Fig. 28d), the sulfate agglomerates consist of Na₂SO₄ (i.e., a residue of the CdS synthesis) along with a variable amount of CdSO₄ [also detected by SR µ-XRD (Fig. 28a)] and minor abundances of sulfite (S⁴⁺) compounds (Na₂SO₃). Sulfates are often associated with Cd(OH)Cl, as revealed by SR µ-XRD and Cl K-edge µ-XANES spectroscopy (Fig. 28a,c,e).
<figure><img src="image_41.png" /><figcaption>**Fig. 28** SR X-ray-based analysis of **a–e** a micro-flake obtained from *The Scream* (ca. 1910) and **f–i** thermally aged Munch’s cadmium yellow lemon oil paint tube (LFG 2.4) (RH ≥ 95%, T = 40 °C, 90 days). **b RGB composite** SR µ-XRD maps of Cd(OH)Cl/CdSO₄/CdCO₃ and SR µ-XRF maps of **b,g S²⁻/S⁶⁺/Cd, c Cl/K, h Na/Cl/Cd**. Selection of **d, i** S K-edge and **e Cl K-edge** XANES spectra (black) and result of the linear combination fitting (LCF) (cyan) of different S-based compounds. In gray, the spectra of selected reference compounds are reported for comparison. Numbers in brackets refer to the spectra showing similar features to those reported (data were collected at ESRF-ID21). Adapted from [102]</figcaption></figure>

The in situ S²⁻ → S⁶⁺ oxidation, with recrystallization of cadmium sulfates in the Cd-/Cl-rich areas, was observed after exposure to high moisture conditions in the dark of a series of oil paint mock-ups, with composition equivalent to that of the flaked yellow area of the lake of *The Scream* (ca. 1910) (Fig. 28f–i).

The results from the micro-flakes of the painting, integrated with those arising from artificially aged paint mock-ups, led to the conclusion that sulfates and sulfites can be interpreted as degradation products of the cadmium yellow paint, with their formation prompted by a highly moist environment and chlorine species. The fact that the formation of CdSO₄ was not observed in Cl-free CdS oil paint mock-ups aged under similar circumstances [125], points out that, under high-humidity levels, the close contact of Cd(OH)Cl [and possibly other (Cd,Cl) compounds] with CdS grains trigger the alteration of CdS oil paints. DFT method investigations allowed the presence of a built-in dipole in Cd(OH)Cl to be highlighted [124], thus explaining the role of Cd(OH)Cl as oxidative catalyst for CdS in an aqueous environment: Cd(OH)Cl
facilitates the transfer of electrons from S²⁻ species in the vicinity of its anodic surface (CdS/Cd(OH)Cl interface) to either OH radicals or H₃O⁺ ions on its cathodic side, thereby prompting the oxidation of CdS to CdSO₄.

### 6.6.3 Extent of crystallinity and photoluminescence properties

Cadmium yellow oil paint discoloration was reported also on Pablo Picasso's painting *Femme* (1907, Foundation Beyeler, Riehen/Basel, Switzerland) [87, 529] and in 26 paintings by Joan Miró (dated around 1970s) belonging to Fundació Miró Mallorca Collection [135].

All the altered areas of these artworks, when analyzed under UV light, show a very intense, reddish or pinkish luminescence (Fig. 27b). Micro-photoluminescence measurements of corresponding cross-sections provided equivalent stratigraphic information at the micro-scale length (Fig. 29a): degraded paints exhibited intense red luminescence (650–700 nm) primarily on the surface, while “intact” paint samples showed only the typical NIR emission (800–870 nm) of CdS, uniformly distributed throughout the paint layer. Based on SR µ-XRD results, such different photoluminescence behavior was ascribed to the extent of crystallinity of CdS: poorly crystalline or nanocrystalline CdS particles (characterized by a high density of surface defects) was found in altered cadmium yellow paints, while highly crystalline CdS phases (hexagonal, cubic, or a mixture of both) were identified in “intact” paints.

A combination of SR µ-XRD and µ-XRF/µ-XANES spectroscopy at the S K-edge from altered cross-sections permitted the presence of a cadmium sulfate hydrate-rich alteration layer at the paint surface to be detected (Fig. 29b, c). In contrast, only compounds resulting from oil/pigment interaction (e.g., oxalates and carboxylates) were found in “intact” paints.

<figure><img src="image_42.png" /><figcaption>**Fig. 29 a** Visible and UV light micrographs of a cross-section taken from an untitled painting by Joan Miró. The surface of the paint layer shows the orangish emission sometimes observed in altered cadmium yellow paints. **b** RGB composite SR µ-XRF maps of Cd/Zn/S (top) and S²⁻/S⁶⁺. **c** Average S K-edge XANES spectra extracted from S²⁻ and S⁶⁺ rich areas of (b) (data collected at ESRF-ID21). Adapted from [135]</figcaption></figure>

<figure><img src="image_43.png" /></figure>
In the painting by Picasso [87], chlorides, present as Cd(OH)Cl and amorphous Cd-Cl compounds, were also identified in the altered sulfate-rich areas characterized by intense reddish emission, thus highlighting again the influence of such species on the oxidative alteration of cadmium yellow paint and in the luminescence properties of CdS.

Overall, the results from the historical case studies above discussed, supported by those arising from mock-ups, show that three primary factors are linked to the degradation process of cadmium yellow paints: (i) exposure to high-humidity conditions (especially when also light is present); (ii) extent of crystallinity of the CdS pigment; (iii) presence of chlorine compounds.

## 6.7 Chrome yellow pigments

### 6.7.1 Properties, manufacturing processes, and analytical characterization

Chrome yellows is a family of pigments that exists in different chemical varieties, either as lead chromate (PbCrO₄, found in nature as the mineral crocoite) or as solid solutions of lead chromate and lead sulfate (PbCr₁-xSxO₄, with 0 ≤ x ≤ 0.8). The shade of these pigments can be gradually tuned from the yellow-orange to pale-yellow by increasing the sulfate content. In addition, when x increases beyond ~ 0.4-0.5, the crystalline structure of PbCr₁-xSxO₄ changes from the monoclinic to the orthorhombic system [233, 520, 541].

The brilliant and forceful hues of chrome yellows offered new ways of artistic expression to late nineteenth-early twentieth century artists, such as Vincent van Gogh, thus becoming part of the pigment palette as soon as they were introduced in the market. In several letters of the period 1888-1890 (e.g., letters nr. 593, 595, 674, 687, 689, 720, 758, 806, 863) and annotated sketches (e.g., F-/JH1463, F-/JH1428 in letter nr. 622 and F-/JH1472 in letter nr. 628), Vincent mentions his use of three varieties of chrome yellow, called as chrome yellow types 1, 2, and 3, which correspond to the 'lemon', 'yellow', and 'orange' shades, respectively [5].

The most used method of preparation of chrome yellows is based on a co-precipitation reaction between a neutral solution or a suspension of a soluble lead salt (acetate, nitrate, chloride, etc.) and an aqueous solution containing different ratios of chromate/dichromate and sulfate salts (usually of potassium or sodium) [541-543]. Since the manufacturing process affects the chemical stability of chrome yellows, their synthesis process has evolved over the years. In this respect, literature describes the chrome yellow production records belonging to the nineteenth century archive database of Winsor & Newton™. Pigments synthesized via these historical methods were employed to prepare paint mock-ups and investigated to gather information on the possible relationship between manufacturing method and the stability of chrome yellow paint films from the chemical and mechanical point view [144, 151, 544, 545].

Chrome yellows have been assigned to the class of photosensitive pigments, considering their tendency to darken under the influence of light [63, 520, 542, 546-548]. Van Gogh, like other artists of his day, was aware of this inconvenience (see letter nr. 595) [5], even though he continued to prefer the use of these pigments up until
his death in July 1890, due to the incomparable effects they gave. The darkening of chrome yellows is a phenomenon visible nowadays in a few iconic paintings, including *the Sunflowers* series by Van Gogh, thus raising questions about which are the safest conditions for their long-term conservation [38, 39, 108, 549].

Since the development of the first synthesis processes during the nineteenth century, it has been suggested that not only specific environmental conditions, but also intrinsic properties of chrome yellows, including the relative abundance of chromium and sulfur, the crystalline structure, the size distribution, and crystal shapes of PbCr₁-xSxO₄, are factors affecting their stability [542, 543, 546, 547].

A wide range of laboratory techniques (employing bench-top and portable devices), including XRD, FT-IR, Raman [63, 109, 151, 233, 354, 544], EPR [106, 107, 143], and EELS [103], in combination with SR-based X-ray methods, such as µ-XRF, XANES spectroscopy at the Cr K-edge, and µ-XRD [63, 106–108, 123, 142–145, 548, 550], have been successfully exploited to understand the origin of darkening of chrome yellows and some of the factors triggering this phenomenon. Such a multi-technique approach has been employed to study photochemically aged paint mock-ups as well as a series of late nineteenth century masterpieces and related paint cross-sections obtained from darkened chrome yellow paints. Specifically, XRD, FT-IR, and Raman spectroscopy allowed different types of chrome yellows to be distinguished by identifying specific spectral markers depending on the sulfate content and crystalline structure [109, 233, 354, 541], whereas EPR, EELS, µ-XRF, and XANES spectroscopy at the Cr K-edge revealed the presence of chromium in different oxidation states (i.e., Cr⁶⁺, Cr⁵⁺, and Cr³⁺) and its stratigraphic distribution within the samples down to the nanometric length scale [63, 103, 106, 107, 143, 144, 548].

The relationship between the structure and electronic properties of different PbCrO₄ and PbCr₁-xSxO₄ varieties have been also examined by DFT methods, thus providing a more in-depth explanation on the role played by sulfur content [551], solubility [552], and p-type semiconductive and optical absorption properties [553] on the lightfastness of each chrome yellow variety.

These aspects will be discussed below, describing selected X-ray results obtained from an integrated approach involving non-invasive MA-XRD investigations of chrome yellow-based paint areas of the Amsterdam *Sunflowers* by Van Gogh (Van Gogh Museum, Amsterdam) (Fig. 30a) and advanced SR-based X-ray micro-analytical studies of paint micro-samples and photochemically aged chrome yellow oil paint mock-ups.

## 6.7.2 Differentiating chrome yellow types

As described above, it is known that Van Gogh made use of different varieties of chrome yellows, each with their own hue and synthesis pathway. By replacing CrO₄²⁻ with increasing amounts of SO₄²⁻ ions within PbCrO₄, the color shifts from a bright yellow-orange to a pale yellow. From a crystallographic perspective, both solid solution end members, PbCrO₄ and PbSO₄, are characterized, respectively, by stable monoclinic and orthorhombic crystal structures [233, 520, 541]. Depending on the amount of sulfate substitution, different effects are apparent within the crystal structure. With a substitution rate of x ~ 0.5, the crystal structure transforms from a monoclinic into an
<figure><img src="image_44.png" /><figcaption>**Fig. 30 a** Photograph of *Sunflowers* (1889) by Vincent van Gogh (Van Gogh Museum, Amsterdam, NL; F458) with arrows pointing to the sampling positions [photo credits: Van Gogh Museum, Amsterdam (Vincent van Gogh Foundation)]. **b** Detail of the painting analyzed by MA-XRD and false color image showing PbCrO₄ (brown) and PbCr₁₋ₓSₓO₄ (x ~ 0.5) (yellow). **c** Diffractogram showing the small shift in diffraction peak position between PbCrO₄ and PbCr₁₋ₓSₓO₄ (x ~ 0.5). PbCrO₄ and PbCr₁₋ₓSₓO₄ (x ~ 0.5) distributions obtained by SR µ-XRD for **d** sample F458/1 and **e** sample F458/4 (data acquired at P06-PETRA III, DESY). Adapted with permission from [108, 109]</figcaption></figure>

orthorhombic unit cell. Additionally, since SO₄²⁻ ions are smaller than CrO₄²⁻ ions, the lattice parameters for both monoclinic and orthorhombic PbCr₁₋ₓSₓO₄ decrease with increasing x [541].

XRD is a highly specific technique to see the change in crystal structure as well as the contraction of the lattice both at the micro- and macro-scale lengths. Indeed, the positions of the diffraction signals progressively shift to higher scattering vector values (Q) with increasing sulfur content [109, 233], as shown in Fig. 30c. Complementary information on the chemical composition and crystalline structure of PbCrO₄/PbCr₁₋ₓSₓO₄ can be obtained also using FT-IR and Raman spectroscopy, as evidenced by the shifts and changes in the shape of bands assigned to the bending and stretching modes [233, 354].

In the Amsterdam *Sunflowers*, three areas (each around 10 × 20 cm²) were non-invasively mapped using MA-XRD in transmission mode (Fig. 30b), which revealed two distinct types of the monoclinic chrome yellow: PbCrO₄ and PbCr₁₋ₓSₓO₄ (x ~ 0.5) [109]. No evidence of the orthorhombic PbCr₁₋ₓSₓO₄ (x > 0.5) was found. The two identified varieties of chrome yellows, namely PbCrO₄ and PbCr₁₋ₓSₓO₄ (x ~ 0.5), could be associated with the chrome yellow types 1 and 2, respectively, as mentioned by Van Gogh in his letters [5]. Sulfur-free PbCrO₄, with a deeper yellow color, was found to be primarily present in the yellow-orange and darker yellow hues of the flower corollas and petals, while the paler yellow sulfur-rich PbCr₁₋ₓSₓO₄ (x ~ 0.5) mostly occurs in the light-yellow tones of the petals. In the light- and dark-green stems and the green flower hearts emerald green was sometimes mixed with PbCr₁₋ₓSₓO₄ (x ~ 0.5); in the orange flower hearts, PbCrO₄ is present
together with emerald green and chrome orange (PbCrO₄·PbO). The latter was identified in multiple orangish brushstrokes. Smaller amounts of PbCr₁⁻ₓSₓO₄ (x ~ 0.5) were also found in mixture with zinc white in the pale-yellow background.

In line with findings of non-invasive MA-XRD studies of the painting, SR µ-XRD mapping and vibrational micro-spectroscopy analysis of cross-sections revealed the presence of a mixture of PbCrO₄ and PbCr₁⁻ₓSₓO₄ (x ~ 0.5) in a sample taken from a yellow-orange petal (Fig. 30d), while only PbCr₁⁻ₓSₓO₄ (x ~ 0.5) was detected in the light-yellow table (Fig. 30e) and in the background, where the yellow pigment is finely mixed with zinc white and viridian (a green Cr³⁺-based pigment: Cr₂O₃·2H₂O) [38, 108]. The latter was identified by non-invasive VIS reflectance spectroscopy measurements [38, 554].

Based on both the non-invasive MA-XRD investigation and the micro-scale analysis of a limited number of samples, it becomes clear that a major part of the chromium containing yellow regions in the painting are made up of PbCr₁⁻ₓSₓO₄ (x ~ 0.5). Sulfur-rich varieties of chrome yellow were also identified in other artworks by Van Gogh and in oil paintings and palettes of other nineteenth-twentieth century artists, such as Paul Cézanne, Paul Gauguin, Séraphine Louis, and Gerardo Dottori [142, 233, 354, 555–557].

The possibility to experimentally distinguish among different chrome yellow types is highly significant, since the susceptibility to darkening of this class of pigments also depends on the sulfate content and crystalline structure [548], as explained in the next paragraph.

### 6.7.3 Causes of darkening

To understand what mechanism of reaction is driving the darkening and how both the environment and the intrinsic properties of chrome yellow paints may influence the extent of color change, studies have been carried out during the past decade on a series of photochemically aged paint mock-ups. Samples were prepared using either historical, commercial, or self-synthesized powders of PbCr₁⁻ₓSₓO₄ with different crystalline structures and different x values (Fig. 31a) [63, 106, 107, 143, 548] sometimes in mixture with different additives/fillers [151, 544, 545].

High lateral resolution Cr K-edge µ-XRF/µ-XANES investigations in XFY detection mode on thin-sectioned samples allowed establishing that the greenish-brown thin layer at the paint surface results from a photo-reduction reaction of the original tetrahedrally coordinated chromate to octahedrally coordinated Cr³⁺ compounds (Fig. 31c). In the XANES spectra the occurrence of this reaction is highlighted by the red-shift of the absorption edge energy and the decreasing of the pre-edge peak intensity at 5.993 keV, assigned to a dipole-forbidden transition from the Cr 1s orbital into orbitals with Cr 3d character (t₂ symmetry) and quantitatively proportional to the Cr⁶⁺-to-total Cr content ratio (Fig. 31d) [63, 548]. Selective and specific Cr speciation information were also more recently obtained by analyzing directly the paint surface of darkened chrome yellow paints by means of Cr K-edge XANES spectroscopy in TEY detection mode (see Sect. 2 for details) [145]. SR µ-XRD mapping has revealed the amorphous nature of the secondary Cr compounds [106].
<figure><img src="image_45.png" /><figcaption>**Fig. 31** *a* Photographs of oil mock-up paints made up of self-synthesized chrome yellow powders differing in sulfate content (CrYₓ denotes PbCr₁₋ₓSₓO₄ with 0 ≤ x ≤ 0.8) and crystalline structure [monoclinic (m) and/or orthorhombic (o)] before (top) and after (bottom) exposure to UVA–VIS light. *b* Cr³⁺-abundance percentage (averaged at the uppermost micrometer of the paint surface) vs. sulfate amount percentage obtained from the light-exposed mock-up paints. Dashed line shows the linear trend. *c* Photomicrograph of a thin section obtained from the self-synthesized CrY₀.₈ paints aged by UVA–VIS light (top) and *d* corresponding RG composite Cr⁶⁺/Cr³⁺ maps. *e* Result of the linear combination fit (cyan) of the µ-XANES spectra of PbCr₀.₂S₀.₈O₄ and one/two Cr³⁺-references [namely: Cr(OH)₃/Cr₂O₃ and Cr³⁺-acetate/Cr³⁺-acetylacetonate] to the ones recorded from the surface of the uppermost alteration layer and the bulk paint of the CrY₀.₈ thin section (black) shown in (*c*) (data of (*c*–*e*) were collected at ESRF-ID21). Adapted with permission from [38, 145, 548]</figcaption></figure>

Sulfate content, crystalline structure, and solubility are among the intrinsic factors prompting the formation of Cr³⁺ compounds in chrome yellows oil paints [63, 107, 548]. The amount of reduced chromium increases with increasing sulfur content, and thus, more soluble sulfur-rich orthorhombic PbCr₁₋ₓSₓO₄ (with x > 0.4) compounds show a higher tendency toward reduction than the less soluble monoclinic sulfur-free PbCrO₄, that is the most lightfast of these materials (Fig. 31b).

The type of binding medium also influences the photo-reduction process of chrome yellows, being more pronounced in the oily medium than in the acrylic one [107]. In the
presence of additives, like CaCO$_3$, the photo-degradation of the oil paint may lead to the formation of calcium oxalate, while the Cr$^{6+}$ → Cr$^{3+}$ conversion takes place [144]. In the presence of specific admixture pigments, such as zinc white, emerald green, and red lead, the rate of light-induced darkening of chrome yellow decreases, possibly as result of the competitive absorption of specific wavelengths between the chrome yellow pigment and the added one, chemical interactions between pigments, and/or electron/positive holes released during light excitation of semiconductor pigments [38].

The darkening of oil paints also depends on the environmental conditions to which the pigment is exposed to. Experiments performed using different wavelengths of the UV–VIS spectrum and commercial WLED systems have established that the reduction of chrome yellow is activated not only by the violet–blue light (i.e., energy range where the pigment shows its maximum of absorption) but also by the green-one [143, 558]. The efficiency of the latter to induce the alteration process could be explained via identification of Cr$^{5+}$ species by EPR spectroscopy. These species, whose formation is favored by the exposure of the paint to humidity and interaction with the oil binder, may absorb radiation in this spectral range, thus may play a key role in driving the photo-reduction toward the formation of different Cr$^{3+}$ compounds [143].

Knowledge acquired from paint mock-ups was exploited for achieving a more com-
prehensive interpretation of the Cr speciation results of chrome yellow cross-sections,
sampled from darkened paints of a series of artworks by Van Gogh [38, 123, 142,
550], such as the Amsterdam *Sunflowers* and *Falling leaves (Les Alyscamps)* (Kröller-
Müller Museum, Otterlo, NL) (Fig. 32a,b). XFY-mode XANES investigations at the
Cr K-edge (both in point analysis and imaging mode) allowed revealing the presence of
Cr$^{3+}$ species either in the form of superficial thin alteration layers or micrometric par-
ticles at the interface between the yellow paint and the superficial restoration varnish
layer (Fig. 32c,e). The fit of the XANES dataset permitted the presence of different
Cr$^{3+}$ compounds to be identified, namely sulfates and oxides. Since the stratigraphic
distribution of Cr$^{3+}$ compounds in paintings was found to be often very similar to
that observed in more light-sensitive paint mock-up [PbCr$_{1-x}$S$_x$O$_4$ (with x > 0.4);
cf. Figure 30d], the darkening of chrome yellow paints was reasonably ascribed to a
chemical degradation of the original pigment driven by a gradual conversion of Cr$^{6+}$
to Cr$^{3+}$ compounds.
<figure><img src="image_46.png" /><figcaption>**Fig. 32** a Photograph of the painting *Falling leaves* (Les Alyscamps) (1888) by Vincent van Gogh (Kröller-Müller Museum, Otterlo; Inv. nr. KM 108.668) (photo credits: Kröller-Müller Museum). b Photomicrograph of the cross-section 224/1 obtained from a sample taken off from the area shown by the arrow in (a). c Quantitative Cr phase maps and corresponding magnification of the regions of interest obtained from the linear combination fitting of the XANES stack collected at the XFM beamline (Australian synchrotron) using the spectra of PbCr<sub>0.5</sub>S<sub>0.5</sub>O<sub>4</sub> (red), Cr(OH)<sub>3</sub> (green), and Cr<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>·H<sub>2</sub>O (blue) as references. d Photomicrograph of sample F458/4, obtained from the light-yellow table of the Amsterdam *Sunflowers* (see Fig. 30a, e for the sampling spots and further results) and relative e RG composite Cr<sup>6+</sup>/Cr<sup>3+</sup> maps acquired at ESRF-ID21. In (e), the relative amounts percentage of Cr<sup>3+</sup> found via Cr K-edge µ-XANES spectroscopy are also reported. Adapted with permission from [108, 123]</figcaption></figure>

**7 Conclusions and perspectives**

In this review, we have described the current state-of-the-art of advanced X-ray methods for the study of alteration of pigments in paintings.

The combination of different X-ray methods (employing conventional sources and synchrotron radiation), often integrated with a wide range of other microscopy and spectroscopic techniques, is a successful strategy to elucidate the complex degradation pathways of certain classes of pigments in paint, from the macro down to the nanometric length scale.

The selected case studies here presented have highlighted that chemical alterations of pigments are due to irreversible reactions, that depend on several factors, including some intrinsic properties of the pigment itself, its manufacturing process, and/or
different environmental parameters (e.g., light, humidity, and air pollutants) to which the painting is exposed to.

From the hundreds of papers here quoted, one can conclude that the heritage science community has shown an increasing interest toward the exploitation of X-ray methods to study paintings degradation phenomena. The interest in SR-based techniques is confirmed by the implementation of new dedicated access modes at some synchrotrons [called block allocation group (BAG)], as it occurred at ESRF [55] and PETRA III-DESY (experiment nr. BAG-20230002 EC) during the last 5 years. Through BAG, experiments are scheduled every 6 months, they facilitate access to beamlines dedicated to structural investigations of materials and favor the development of activities and interactions of heritage researchers.

Next to the X-rays methods described in this review (namely XRF, XAS, and XRD) other state-of-the-art SR-based X-ray techniques are expected to find application for the study of the alteration processes of pigments in the future, namely: X-ray Raman scattering (XRS) and X-ray excited optical luminescence (XEOL). So far, such methods were already used for the characterization of organic components in archaeological/paleontological objects [559–561] and for the investigation of structural and optical properties of semiconducting phases [562, 563]. In particular, the development of new XEOL set-ups for lifetime measurements, full-field multispectral imaging (PUMA beamline, SOLEIL; Paris, France), and hyperspectral mapping (Carauába beamline, Sirius; São Paulo, Brazil) are opening new possibilities for probing crystal defects and impurities associated with the manufacturing process of artists’ pigments and their potential reactivity within historical paint layers down to the sub-micrometer length scale [174, 564].

Further, the latest instrumental developments allow acquiring today massive amounts of datasets in a short time, thus calling upon smart statistical data evaluation, and analysis. Particularly promising perspectives concern the systematic integration of a wide range of available software with new algorithms/tools based on machine learning methods.

Still, due to the complexity of oil paints and current challenges associated both with object- and sample-based macro/micro-analysis, a lot of efforts are regularly ongoing to optimize the preparation of reliable mock-ups, whose study is fundamental for a deeper understanding of data recorded on historical paintings.

From the point of view of preventive conservation, the outcomes here described are providing important bases for the development of effective monitoring strategies for the safeguard of artworks at risk of degradation. In addition, they form a significant contribution toward the development of models for the virtual reconstruction of the original appearance of altered artworks and for the prediction of their evolution over time, when adequate safeguard measures are not implemented.

**Acknowledgements** The authors acknowledge the following Editors for the permission to reprint/adapt the following Figures: RSC for Figures 1a,b, 18, 23a-c, 32a-c; Springer Nature for Figures 8, 22a-f, 27b, 29; ACS for Figures 6, 20b,c, 24, 25, 31; Wiley for Figures 6, 10, 16, 30, 32d,e; Elsevier for Figures 9,19, 31; MDPI for Figures 11,14; De Gruyter for Figure 15; Science Advances for Figures 1c, 23d-f, 27a, 28; APS for Figure 26; Amsterdam University Press-Van Gogh Museum for Figure 31. The authors warmly thank also all the collaborators, institutes, museums, and heritage sites involved in the different research projects presented here.
**Author contributions** All authors contributed to the conception and design of the manuscript. Material preparation, data collection, and analysis were performed by all authors. The first draft of the manuscript was written by all authors and all authors commented on previous versions of the manuscript. All authors read and approved the final version of the manuscript.

**Funding** The research was financially supported by: Horizon 2020 project IPERION-HS (H2020-INFRAIA-2019-1, GA nr. 871034); the Horizon Europe project PERCEIVE (HORIZON-CL2-2021-HERITAGE-01, GA nr. 101061157); the project PE 0000020 CHANGES—CUP: B53C22003890006, NRP Mission 4 Component 2 Investment 1.3, funded by the European Union—NextGenerationEU, under the Italian Ministry of University and Research (MUR); Interreg "Vlaanderen-Nederland" project Smart-Light 2.0; the BeAM (Belgian Avant Garde Modernism) project of BELSPO (Brussels, Belgium); the NanoLight Center of Excellence (Research Council, University of Antwerp, Belgium); the grant TED2021-129299A-100 funded by MCIN/AEI/10.13039/501100011033; the Research Foundation Flanders (FWO) through its program on PhD Fellowships in Fundamental Research (application nr. 1181221N, 1181223N, 1183123N, and 1183125N). Koen Janssens and Geert Van der Snickt are indebted to the UAntwerp BOF DOCPRO project on lead-white speciation (project ID 44608). This research was also part of the activities of the Chair on Advanced Imaging Techniques for the Arts, established by the Baillet Latour fund. Koen Janssens, Ermanno Avranovich Clerici, and Steven De Meyer acknowledge financial support from the Fund for Scientific Research, Brussels, via project AutomatED (FN 7022, contract S000121N). Laura Cartechini, Francesca Rosi, and Aldo Romani thank the European Union—NextGenerationEU, Mission 4, Component 2, under the Italian Ministry of University and Research (MUR) National Innovation Ecosystem grant ECS00000041—VITALITY—CUP B43C22000470005. Katrien Keune, Fréderique T. H. Broers, and Nouchka De Keyser acknowledge the support by the Netherlands Institute for Conservation + Art + Science + (NICAS) and the Dutch Research Council (NWO) (3D2P Project, Project Nr. 628.007.031). Marine Cotte thanks the Royal Netherlands Academy of Arts and Sciences, KNAW (Descartes Huygens price 2018), and the PHC Van Gogh granted by the French Ministries of European and Foreign Affairs, and of Higher Education, Research and Innovation.

**Data availability** The datasets generated during and/or analyzed during the current study are available from the corresponding authors on reasonable request.

**Declarations**

**Conflict of interest** The authors have no financial or non-financial interests to disclose.

**Open Access** This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

**References**

1. Plinio, Storia Naturale - V (Einaudi, Torino, 1988)

2. C. Cennini, F. Frezzato, Il libro dell'arte (Neri Pozza, Milano, 2003)

3. G. P. Lomazzo, Chapters 5–7, in: Trattato Dell’Arte Della Pittura, Scultura Ed Architettura - Volume 1, ed. By S. Del Monte (Roma, 1844), pp. 328–333

4. C. Pissarro, Eragny [May 31st, 1887], in: Letters to His Son Lucien, ed. By J. Rewald 2nd ed., (Pantheon Books Inc., New York, 1943), pp. 113–114

5. L. Jansen, H. Luijten, N. Bakker, Vincent van Gogh – The Letters (Thames & Hudson Ltd., London and Amsterdam, 2009). http://vangoghletters.org/vg/letters.html. Accessed June 2025
6. R. Nöller, Cinnabar reviewed: characterization of the red pigment and its reactions. Stud. Conserv. **60**, 79–87 (2015). https://doi.org/10.1179/2047058413Y.0000000089

7. M. Cotte, J. Susini, N. Metrich, A. Moscato, C. Gratziu, A. Bertagnini, M. Pagano, Blackening of Pompeian cinnabar paintings: X-ray microspectroscopy analysis. *Anal. Chem.* **78**, 7484–7492 (2006). https://doi.org/10.1021/ac0612224

8. S. Pérez-Diez, A. Pitarch Martí, A. Giakoumaki, N. Prieto-Taboada, S. Fdez-Ortiz de Vallejuelo, A. Martellone, B. De Nigris, M. Osanna, J. M. Madariaga, M. Maguregui, When Red Turns Black: Influence of the 79 AD Volcanic Eruption and Burial Environment on the Blackening/Darkening of Pompeian Cinnabar. *Anal. Chem.* **93**, 15870–15877 (2021). https://doi.org/10.1021/acs.analchem.1c02420

9. A. Roy, Artists' pigments. A handbook of their history and characteristics-Volume 2 (National Gallery of Art and Oxford University Press, Washington and Oxford, 1993)

10. M. Spring, R. Grout, The blackening of vermilion: an analytical study of the process in paintings. *Natl. Gallery Tech. Bull.* **23**, 50–61 (2002)

11. K. Keune, J.J. Boon, Analytical imaging studies clarifying the process of the darkening of vermilion in paintings. *Anal. Chem.* **77**, 4742–4750 (2005). https://doi.org/10.1021/ac048158f

12. M. Radepont, W. De Nolf, K. Janssens, G. Van Der Snickt, Y. Coquinot, L. Klaassen, M. Cotte, The use of microscopic X-ray diffraction for the study of HgS and its degradation products corderoite (α-Hg₃S₂Cl₂), kenhsuite (γ-Hg₃S₂Cl₂) and calomel (Hg₂Cl₂) in historical paintings. *J. Anal. At. Spectrom.* **26**, 959–968 (2011). https://doi.org/10.1039/c0ja00260g

13. M. Vagnini, R. Vivani, E. Viscuso, M. Favazza, B.G. Brunetti, A. Sgamellotti, C. Miliani, Investigation on the process of lead white blackening by Raman spectroscopy, XRD and other methods: study of Cimabue's paintings in Assisi. *Vib. Spectrosc.* **98**, 41–49 (2018). https://doi.org/10.1016/j.vibspec.2018.07.006

14. E. Avranovich Clerici, S. de Meyer, F. Vanmeert, S. Legrand, L. Monico, C. Miliani, K. Janssens, Multi-scale X-ray imaging of the pigment discoloration processes triggered by chlorine compounds in the upper Basilica of Saint Francis of Assisi. *Molecules* **28**, 6106 (2023). https://doi.org/10.3390/molecules28166106

15. A. Mignosi Tantillo, Restauri alla basilica inferiore di Assisi. *Bollettino d'Arte* **5**, 217–223 (1975)

16. F. Corsini, A. De Marchi, V. Picchiarelli, G. Verdiani, E. Zappasodi, Un esercizio di anastilosi digitale nella basilica inferiore di San Francesco ad Assisi, in: *Il Maestro Di San Francesco e Lo Stil Novo Del Duecento Umbro, eds. By A. De Marchi, V. Picchiarelli, E. Zappasodi* (Silvana Editoriale, Milano, 2024), pp. 193–211

17. V. Gonzalez, I. Fazlic, M. Cotte, F. Vanmeert, A. Gestels, S. De Meyer, F. Broers, J. Hermans, A. van Loon, K. Janssens, P. Noble, K. Keune, Lead(II) formate in Rembrandt's Night Watch: detection and distribution from the macro- to the micro-scale. *Angewandte Chemie – Int. Ed.* **62**, e202216478 (2023). https://doi.org/10.1002/anie.202216478

18. S. De Meyer, F. Vanmeert, R. Vertongen, A. van Loon, V. Gonzalez, G. van der Snickt, A. Vandivere, K. Janssens, Imaging secondary reaction products at the surface of Vermeer's Girl with the Pearl Earring by means of macroscopic X-ray powder diffraction scanning. *Herit. Sci.* **7**, 67 (2019). https://doi.org/10.1186/s40494-019-0309-3

19. F. Vanmeert, G. Van der Snickt, K. Janssens, Plumbonacrite identified by X-ray powder diffraction tomography as a missing link during degradation of red lead in a Van Gogh painting. *Angewandte Chemie – Int. Ed.* **54**, 3607–3610 (2015). https://doi.org/10.1002/anie.201411691

20. M. Spring, New insights into the materials of fifteenth- and sixteenth-century Netherlandish paintings in the National Gallery, London. *Herit. Sci.* **5**, 40 (2017). https://doi.org/10.1186/s40494-017-0152-3

21. K. Schnetz, A.A. Gambardella, R. van Elsas, J. Rosier, E.E. Steenwinkel, A. Wallert, P.D. Iedema, K. Keune, Evidence for the catalytic properties of ultramarine pigment. *J. Cult. Herit.* **45**, 25–32 (2020). https://doi.org/10.1016/j.culher.2020.04.002

22. A. van Loon, A.A. Gambardella, V. Gonzalez, M. Cotte, W. De Nolf, K. Keune, E. Leonhardt, S. de Groot, A.N. Proaño Gaibor, A. Vandivere, Out of the blue: Vermeer's use of ultramarine in Girl with a Pearl Earring. *Herit. Sci.* **8**, 25 (2020). https://doi.org/10.1186/s40494-020-00364-5

23. E. Cato, C. Borca, T. Huthwelker, E.S.B. Ferreira, Aluminium X-ray absorption near-edge spectroscopy analysis of discoloured ultramarine blue in 20th century oil paintings. *Microchem.* **J.** **126**, 18–24 (2016). https://doi.org/10.1016/j.microc.2015.11.021

24. J.S. Ferrer, I.C.A. Sandu, T. Syversen, A.M. Cardoso, A. Candeias, C.N. Borca, Investigating Colour Changes in Red and Blue Paints - A Preliminary Study of Art Materials and Techniques in Edvard
Munch's Old Man in Warnemünde (1907), in: Conservation of Modern Oil Paintings (Springer International Publishing, 2020), pp. 209–218. https://doi.org/10.1007/978-3-030-19254-9_15

25. P. Noble, A. van Loon, J. Bikker, Rembrandt's The Standard Bearer: New Findings from Imaging Analyses. Rijksmuseum Bulletin **71**, 170–179 (2023). https://doi.org/10.52476/trb.15070

26. P. Santopadre, M. Verità, A study of smalt and its conservation problems in two sixteenth-century wall paintings in Rome. Stud. Conserv. **51**, 29–40 (2006). https://doi.org/10.1179/sic.2006.51.1.29

27. C. de Mecquenem, M. Eveno, M. Alfeld, R. Pillay, E. Laval, E. Ravaud, I. Reiche, A multimodal study of smalt preservation and degradation on the painting “Woman doing a Libation or Artemisia” from an anonymous painter of the Fontainebleau School. Eur. Phys. J. Plus **138**, 185 (2023). https://doi.org/10.1140/epjp/s13360-023-03799-4

28. C. de Mecquenem, M. Eveno, D. Zurbach, K. Mösl, M. Cotte, I. Reiche, Influence of the painting medium on the alteration process of smalt in oil paintings studied using combined K and Co K-edge XANES. Appl. Phys. A Mater. Sci. Process. **130**, 781 (2024). https://doi.org/10.1007/s00339-024-07943-4

29. M. Spring, C. Higgitt, D. Saunders, Investigation of pigment-medium interaction processes in oil paint containing degraded smalt. Natl. Gallery Tech. Bull. **26**, 56–70 (2005)

30. A. Vila, K. Monrad, T. Filtenborg, J. Wadum, As Time Passed by Came Sunset. Christen Købke's View of Lake Sortedam, its Genesis and Colour Changes, in: Science and Art: The Painted Surface, eds. By A. Sgamellotti, B.G. Brunetti, C. Miliani (Royal Society of Chemistry, 2014), pp. 354–372. https://doi.org/10.1039/9781839161957-00354

31. M. Vermeulen, G. Nuyts, J. Sanyova, A. Vila, D. Buti, J.P. Suuronen, K. Janssens, Visualization of As(III) and As(V) distributions in degraded paint micro-samples from Baroque- and Rococo-era paintings. J. Anal. At. Spectrom. **31**, 1913–1921 (2016). https://doi.org/10.1039/c6ja00134c

32. N. De Keyser, F. Broers, F. Vanmeert, S. De Meyer, F. Gabrieli, E. Hermens, G. Van der Snickt, K. Janssens, K. Keune, Reviving degraded colors of yellow flowers in 17th century still life paintings with macro- and microscale chemical imaging. Sci. Adv. **8**, eabn6344 (2022). https://doi.org/10.1126/sciadv.abn6344

33. J. Simoen, S. De Meyer, F. Vanmeert, N. de Keyser, E. Avranovich, G. Van der Snickt, A. Van Loon, K. Keune, K. Janssens, Combined Micro- and Macro scale X-ray powder diffraction mapping of degraded Opment paint in a 17th century still life painting by Martinus Nellius. Herit. Sci. **7**, 83 (2019). https://doi.org/10.1186/s40494-019-0324-4

34. G. Van Der Snickt, J. Dik, M. Cotte, K. Janssens, J. Jaroszewicz, W. De Nolf, J. Groenewegen, L. Van Der Loeff, Characterization of a degraded cadmium yellow (CdS) pigment in an oil painting by means of synchrotron radiation based X-ray techniques. Anal. Chem. **81**, 2600–2610 (2009). https://doi.org/10.1021/ac802518z

35. T. Froysaker, N. Streeton, H. Kutzke, F. Hanssen-Bauer, B. Topalova-Casadiego, Public Paintings by Edvard Munch and His Contemporaries: Change and Conservation Challenges (Archetype Publications Ltd, London, 2015)

36. J.L. Mass, R. Opila, B. Buckley, M. Cotte, J. Church, A. Mehta, The photodegradation of cadmium yellow paints in Henri Matisse's le Bonheur de vivre (1905–1906). Appl. Phys. A Mater. Sci. Process. **111**, 59–68 (2013). https://doi.org/10.1007/s00339-012-7418-0

37. F. Casadio, S. Xie, S.C. Rukes, B. Myers, K.A. Gray, R. Warta, I. Fiedler, Electron energy loss spectroscopy elucidates the elusive darkening of zinc potassium chromate in Georges Seurat's A Sunday on la Grande Jatte-1884. Anal. Bioanal. Chem. **399**, 2909–2920 (2011). https://doi.org/10.1007/s00216-010-4264-9

38. L. Monico, E. Hendriks, M. Geldof, C. Miliani, K. Janssens, B. G. Brunetti, M. Cotte, F. Vanmeert, A. Chieli, G. Van der Snickt, A. Romani, M. J. Melo, Chemical Alteration and Colour Changes in the Amsterdam Sunflowers, in: Van Gogh's Sunflowers Illuminated, eds. By E. Hendriks, M. Vellekoop, M. van Bommel, M. Geldof (Amsterdam University Press and Van Gogh Museum, Amsterdam, 2019), pp. 125–157. https://doi.org/10.1515/9789048550531-006

39. C. Higgitt, G. Macaro, M. Spring, Methods, materials and condition of the London Sunflowers, in: Van Gogh's Sunflowers Illuminated, eds. By E. Hendriks, M. Vellekoop, M. van Bommel, M. Geldof (Amsterdam University Press and Van Gogh Museum, Amsterdam, 2019), pp. 49–84. https://doi.org/10.1017/9789048550531.004

40. L. van Tilborgh, E. Hendriks, Vincent Van Gogh Paintings: Antwerp and Paris, 1885–1888, vol. 2 (Waanders Publishers and Van Gogh Museum, Zwolle and Amsterdam, 2011)
41. M. Alter, L. Binet, N. Touati, N. Lubin-Germain, A.S. Le Hô, F. Mirambet, D. Gourier, Photochemical origin of the darkening of copper acetate and resinate pigments in historical paintings. Inorg. Chem. **58**, 13115–13128 (2019). https://doi.org/10.1021/acs.inorgchem.9b02007

42. L. Cartechini, C. Miliani, B.G. Brunetti, A. Sgamellotti, C. Altavilla, E. Ciliberto, F. D'Acapito, X-ray absorption investigations of copper resinate blackening in a XV century Italian painting. Appl. Phys. A Mater. Sci. Process. **92**, 243–250 (2008). https://doi.org/10.1007/s00339-008-4498-y

43. N. Salvadó, S. Butí, M. Cotte, G. Cinque, T. Pradell, Shades of green in 15th century paintings: combined microanalysis of the materials using synchrotron radiation XRD, FTIR and XRF. Appl. Phys. A Mater. Sci. Process. **111**, 47–57 (2013). https://doi.org/10.1007/s00339-012-7483-4

44. K. Keune, J. Mass, A. Mehta, J. Church, F. Meirer, Analytical imaging studies of the migration of degraded orpiment, realgar, and emerald green pigments in historic paintings and related conservation issues. Herit. Sci. **4**, 10 (2016). https://doi.org/10.1186/s40494-016-0078-1

45. K. Keune, J.J. Boon, R. Boitelle, Y. Shimadzu, Degradation of emerald green in oil paint and its contribution to the rapid change in colour of the Descente des vaches (1834–1835) painted by Théodore Rousseau. Stud. Conserv. **58**, 199–210 (2013). https://doi.org/10.1179/2047058412Y.0000000063

46. L. Monico, S. Prati, G. Sciutto, E. Catelli, A. Romani, D.Q. Balbas, Z. Li, S. De Meyer, G. Nuyts, K. Janssens, M. Cotte, J. Garrevoet, G. Falkenberg, V.I. Tardillo Suarez, R. Tucoulou, R. Mazzeo, Development of a multi-method analytical approach based on the combination of synchrotron radiation X-ray micro-analytical techniques and vibrational micro-spectroscopy methods to unveil the causes and mechanism of darkening of “fake-gilded” decorations in a Cimabue painting. J. Anal. At. Spectrom. **37**, 114–129 (2022). https://doi.org/10.1039/d1ja00271f

47. F. Casadio, K. Keune, P. Noble, A. Van Loon, E. Hendriks, S.A. Centeno, G. Osmond, Metal Soaps in Art: Conservation and Research (Springer International Publishing, Switzerland, 2019)

48. F.C. Izzo, M. Kratter, A. Nevin, E. Zendri, A Critical review on the analysis of metal soaps in oil paintings. ChemistryOpen **10**, 904–921 (2021). https://doi.org/10.1002/open.202100166

49. S. Russo, L. Brambilla, J.B. Thomas, E. Joseph, But aren't all soaps metal soaps? A review of applications, physico-chemical properties of metal soaps and their occurrence in cultural heritage studies. Herit. Sci. **11**, 172 (2023). https://doi.org/10.1186/s40494-023-00988-3

50. K. Janssens, M. Alfeld, G. Van Der Snickt, W. De Nolf, F. Vanmeert, M. Radepont, L. Monico, J. Dik, M. Cotte, G. Falkenberg, C. Miliani, B.G. Brunetti, The use of synchrotron radiation for the characterization of artists' pigments and paintings. Annu. Rev. Anal. Chem. **6**, 399–425 (2013). https://doi.org/10.1146/annurev-anchem-062012-092702

51. K. Janssens, G. Van der Snickt, F. Vanmeert, S. Legrand, G. Nuyts, M. Alfeld, L. Monico, W. Anaf, W. De Nolf, M. Vermeulen, J. Verbeeck, K. De Wael, Non-invasive and non-destructive examination of artistic pigments, paints, and paintings by means of X-ray methods. Top. Curr. Chem. **374**, 81 (2016). https://doi.org/10.1007/s41061-016-0079-2

52. C. Miliani, L. Monico, M.J. Melo, S. Fantacci, E.M. Angelin, A. Romani, K. Janssens, Photochemistry of artists' dyes and pigments: towards better understanding and prevention of colour change in works of art. Angewandte Chemie – Int. Ed. **57**, 7324–7334 (2018). https://doi.org/10.1002/anie.201802801

53. K. Janssens, M. Cotte, Using synchrotron radiation for characterization of cultural heritage materials, in: Synchrotron Light Sources and Free-Electron Lasers: Accelerator Physics, Instrumentation and Science Applications (2020), pp. 2457–2483. https://doi.org/10.1007/978-3-030-23201-6_78

54. L. Bertrand, L. Robinet, M. Thoury, K. Janssens, S.X. Cohen, S. Schöder, Cultural heritage and archaeology materials studied by synchrotron spectroscopy and imaging. Appl. Phys. A Mater. Sci. Process. **106**, 377–396 (2012). https://doi.org/10.1007/s00339-011-6686-4

55. M. Cotte, V. Gonzalez, F. Vanmeert, L. Monico, C. Dejoie, M. Burghammer, L. Huder, W. De Nolf, S. Fisher, I. Fazlic, C. Chauffeton, G. Wallez, N. Jiménez, F. Albert-Tortosa, N. Salvadó, E. Possenti, C. Colombo, M. Ghirardello, D. Comelli, E. Avranovich Clerici, R. Vivani, A. Romani, C. Costantino, K. Janssens, Y. Taniguchi, J. McCarthy, H. Reichert, J. Susini, The “Historical Materials BAG”: a new facilitated access to synchrotron X-ray diffraction analyses for cultural heritage materials at the european synchrotron radiation facility. Molecules **27**, 1997 (2022). https://doi.org/10.3390/molecu les27061997

56. A. Gianoncelli, S. Schöder, J.R. Plaisier, M. Fugazzotto, G. Barone, A. Russo, P. Mazzoleni, S. Raneri, X-ray synchrotron radiation to look at pigments in antiquities: overview and examples. Heritage **7**, 2118–2137 (2024). https://doi.org/10.3390/heritage7040100
57. P. Sedigh Rahimabadi, M. Khodaei, K.R. Koswattage, Review on applications of synchrotron-based X-ray techniques in materials characterization. X-Ray Spectrom. **49**, 348–373 (2020). https://doi.org/10.1002/xrs.3141

58. Y. Liu, X. Su, J. Ding, J. Zhou, Z. Liu, X. Wei, H. Yang, B. Liu, Progress and challenges in structural, in situ and operando characterization of single-atom catalysts by X-ray based synchrotron radiation techniques. Chem. Soc. Rev. **53**, 11850–11887 (2024). https://doi.org/10.1039/D3CS00967J

59. F. Meirer, B.M. Weckhuysen, Spatial and temporal exploration of heterogeneous catalysts with synchrotron radiation. Nat. Rev. Mater. **3**, 324–340 (2018). https://doi.org/10.1038/s41578-018-0044-5

60. C. Cao, M.F. Toney, T.K. Sham, R. Harder, P.R. Shearing, X. Xiao, J. Wang, Emerging X-ray imaging technologies for energy materials. Mater. Today **34**, 132–147 (2020). https://doi.org/10.1016/j.mattod.2019.08.011

61. H. Hu, J. Zhao, L. Wang, L. Shang, L. Cui, Y. Gao, B. Li, Y.F. Li, Synchrotron-based techniques for studying the environmental health effects of heavy metals: current status and future perspectives. Trends Anal. Chem. **122**, 115721 (2020). https://doi.org/10.1016/j.trac.2019.115721

62. C. Sanchez-Cano, R.A. Alvarez-Puebla, J.M. Abendroth, T. Beck et al., X-ray-based techniques to study the nano-bio interface. ACS Nano **15**, 3754–3807 (2021). https://doi.org/10.1021/acsnano.0c09563

63. L. Monico, G. Van Der Snickt, K. Janssens, W. De Nolf, C. Miliani, J. Verbeeck, H. Tian, H. Tan, J. Dik, M. Radepont, M. Cotte, Degradation process of lead chromate in paintings by Vincent van Gogh studied by means of synchrotron X-ray spectromicroscopy and related methods. 1. Artificially aged model samples. Anal. Chem. **83**, 1214–1223 (2011). https://doi.org/10.1021/ac102424h

64. L. Zanella, F. Casadio, K.A. Gray, R. Warta, Q. Ma, J.F. Gaillard, The darkening of zinc yellow: XANES speciation of chromium in artist's paints after light and chemical exposures. J. Anal. At. Spectrom. **26**, 1090–1097 (2011). https://doi.org/10.1039/c0ja00151a

65. K. Keune, J. Mass, F. Meirer, C. Pottasch, A. Van Loon, A. Hull, J. Church, E. Pouyet, M. Cotte, A. Mehta, Tracking the transformation and transport of arsenic sulfide pigments in paints: synchrotron-based X-ray micro-analyses. J. Anal. At. Spectrom. **30**, 813–827 (2015). https://doi.org/10.1039/c4ja00424h

66. L. Robinet, M. Spring, S. Pagès-Camagna, D. Vantelon, N. Trcera, Investigation of the discoloration of smalt pigment in historic paintings by micro-X-ray absorption spectroscopy at the Co K-edge. Anal. Chem. **83**, 5145–5152 (2011). https://doi.org/10.1021/ac200184f

67. I. Cianchetta, I. Colantoni, F. Talarico, F. D'Acapito, A. Trapananti, C. Maurizio, S. Fantacci, I. Davoli, Discoloration of the smalt pigment: experimental studies and ab initio calculations. J. Anal. At. Spectrom. **27**, 1941–1948 (2012). https://doi.org/10.1039/c2ja30132f

68. L. Samain, G. Silversmit, J. Sanyova, B. Vekemans, H. Salomon, B. Gilbert, F. Grandjean, G.J. Long, R.P. Hermann, L. Vincze, D. Strivay, Fading of modern Prussian blue pigments in linseed oil medium. J. Anal. At. Spectrom. **26**, 930–941 (2011). https://doi.org/10.1039/c0ja00234h

69. L. Samain, F. Grandjean, G.J. Long, P. Martinetto, P. Bordet, J. Sanyova, D. Strivay, Synthesis and fading of eighteenth-century Prussian blue pigments: a combined study by spectroscopic and diffractive techniques using laboratory and synchrotron radiation sources. J. Synchrotron Radiat. **20**, 460–473 (2013). https://doi.org/10.1107/S0909049513004585

70. F. Grandjean, L. Samain, G.J. Long, Characterization and utilization of Prussian blue and its pigments. Dalton Trans. **45**, 18018–18044 (2016). https://doi.org/10.1039/c6dt03351b

71. M. Vermeulen, J. Sanyova, K. Janssens, G. Nuyts, S. De Meyer, K. De Wael, The darkening of copper- or lead-based pigments explained by a structural modification of natural orpiment: a spectroscopic and electrochemical study. J. Anal. At. Spectrom. **32**, 1331–1341 (2017). https://doi.org/10.1039/c7ja00047b

72. H. Howard, J. Najorka, P.F. Schofield, K. Geraki, Degradation of fourteenth-century mordant gilding layers: synchrotron-based microfocus XRF, XRD, and XANES analyses of two paintings by Pietro Lorenzetti. Stud. Conserv. **69**, 193–208 (2024). https://doi.org/10.1080/00393630.2023.2201094

73. V. Gonzalez, A. Van Loon, S. Wt Price, P. Noble, K. Keune, Synchrotron micro-XRD and micro-XRD-CT reveal newly formed lead-sulfur compounds in Old Master paintings. J. Anal. At. Spectrom. **35**, 2267–2273 (2020). https://doi.org/10.1039/d0ja00169d

74. N. Salvadó, T. Pradell, E. Pantos, M.Z. Papiz, J. Molera, M. Seco, M. Vendrell-Saz, Identification of copper-based green pigments in Jaume Huguet's Gothic altarpieces by Fourier transform infrared microspectroscopy and synchrotron radiation X-ray diffraction. J. Synchrotron Radiat. **9**, 215–222 (2002). https://doi.org/10.1107/S0909049502007859
75. N. Salvadó, S. Butí, J. Nicholson, H. Emerich, A. Labrador, T. Pradell, Identification of reaction compounds in micrometric layers from gothic paintings using combined SR-XRD and SR-FTIR. *Talanta* **79**, 419-428 (2009). https://doi.org/10.1016/j.talanta.2009.04.005

76. N. Salvadó, S. Butí, A. Labrador, G. Cinque, H. Emerich, T. Pradell, SR-XRD and SR-FTIR study of the alteration of silver foils in medieval paintings. *Anal. Bioanal. Chem.* **399**, 3041–3052 (2011). https://doi.org/10.1007/s00216-010-4365-5

77. E. Welcome, P. Walter, P. Bleuet, J.L. Hodeau, E. Dooryhee, P. Martinetto, M. Menu, Classification of lead white pigments using synchrotron radiation micro X-ray diffraction. *Appl. Phys. A Mater. Sci. Process.* **89**, 825–832 (2007). https://doi.org/10.1007/s00339-007-4217-0

78. V. Gonzalez, G. Wallez, T. Calligaro, M. Cotte, W. De Nolf, M. Eveno, E. Ravaud, M. Menu, Synchrotron-based high angle resolution and high lateral resolution X-ray diffraction: revealing lead white pigment qualities in old masters paintings. *Anal. Chem.* **89**, 13203–13211 (2017). https://doi.org/10.1021/acs.analchem.7b02949

79. V. Gonzalez, T. Calligaro, G. Wallez, M. Eveno, K. Toussaint, M. Menu, Composition and microstructure of the lead white pigment in Masters paintings using HR Synchrotron XRD. *Microchem. J.* **125**, 43–49 (2016). https://doi.org/10.1016/j.microc.2015.11.005

80. N. Palladino, M. Occelli, G. Wallez, Y. Coquinot, Q. Lemasson, L. Pichon, S. Stankic, V. Etgens, J. Salvant, An analytical survey of zinc white historical and modern artists' materials. *Herit. Sci.* **12**, 47 (2024). https://doi.org/10.1186/s40494-023-01082-4

81. C.I. Hiley, G. Hansford, N. Eastaugh, High-resolution non-invasive X-ray diffraction analysis of artists' paints. *J. Cult. Herit.* **53**, 1–13 (2022). https://doi.org/10.1016/j.culher.2021.10.008

82. L. Dalecky, I. Bonaduce, É. Anheim, J. La Nasa, M. L'Héronde, C. Morel, E. Catelli, S. Prati, Z. Li, L. Beck, I. Caffy, E. Delqué-Količ, A. Chevalier, L. Bertrand, A typical postwar workshop: Insights into Simon Hantai's oil paint palette. *J. Cult. Herit.* **66**, 511–522 (2024). https://doi.org/10.1016/j.culher.2023.11.019

83. C. Costantino, L. Monico, F. Rosi, R. Vivani, A. Romani, L.C. Colocho Hurtarte, E. Villalobos-Portillo, C.J. Sahle, T. Huthwelker, C. Dejoie, M. Burghammer, M. Cotte, Non-destructive and non-invasive approaches for the identification of hydroxy lead-calcium phosphate solid solutions (PbₓCa₁₋ₓ)₅(PO₄)₃OH) in cultural heritage materials. *Appl. Spectrosc.* **78**, 1231–1244 (2024). https://doi.org/10.1177/00037028241243375

84. L. Dalecky, F. Sottile, L. Hung, L. Cazals, A. Desolneux, A. Chevalier, J.P. Rueff, L. Bertrand, Non-resonant inelastic X-ray scattering for discrimination of pigments. *Phys. Chem. Chem. Phys.* **26**, 4363–4371 (2023). https://doi.org/10.1039/d3cp04753a

85. M. Thoury, J.P. Echard, M. Réfrégiers, B. Berrie, A. Nevin, F. Jamme, L. Bertrand, Synchrotron UV-visible multispectral luminescence microimaging of historical samples. *Anal. Chem.* **83**, 1737–1745 (2011). https://doi.org/10.1021/ac102986h

86. S. Hageraats, K. Keune, M. Thoury, R. Hoppe, A Synchrotron Photoluminescence Microscopy Study into the Use and Degradation of Zinc White in 'The Woodcutters' by Bart van der Leck, in: Conservation of Modern Oil Paintings, ed. By K. J. van den Berg, I. Bonaduce, A. Burnstock, B. Ormsby, M. Scharff, L. Carlyle, G. Heydenreich, K. Keune (Springer, Cham., 2020), pp. 275–288. https://doi.org/10.1007/978-3-030-19254-9_21

87. M. Ghirardello, V. Gonzalez, L. Monico, A. Nevin, D. MacLennan, C.S. Patterson, M. Burghammer, M. Réfrégiers, D. Comelli, M. Cotte, Application of synchrotron radiation-based micro-analysis on cadmium Yellows in Pablo Picasso's Femme. *Microsc. Microanal.* **28**, 1504–1513 (2022). https://doi.org/10.1017/S1431927622000873

88. A. Rogalev, J. Goulon, X-ray Excited Optical Luminescence Spectroscopies, in: Chemical Applications of Synchrotron Radiation. Part II: X-Ray Applications, ed. By T. K. Sham (World Scientific, 2002), pp. 707–760. https://doi.org/10.1142/9789812775757_0015

89. T.K. Sham, Photon-in/photon-out spectroscopic techniques for materials analysis: some recent developments. *Adv. Mater.* **26**, 7896–7901 (2014). https://doi.org/10.1002/adma.201304349

90. L. Liu, X. Sun, X-ray Excited Optical Luminescence and Its Applications, in: Synchrotron Radiation Applications, ed. By X. Zhang (World Scientific, 2018), pp. 493–534. https://doi.org/10.1142/978-8132276757_0012

91. S. Hageraats, K. Keune, S. Stanescu, J.M. Laurent, W. Fresquet, M. Thoury, Combining X-ray excited optical luminescence and X-ray absorption spectroscopy for correlative imaging on the nanoscale. *J. Synchrotron Radiat.* **28**, 1858–1864 (2021). https://doi.org/10.1107/S1600577521009450
92. P. Reischig, L. Helfen, A. Wallert, T. Baumbach, J. Dik, High-resolution non-invasive 3D imaging of paint microstructure by synchrotron-based X-ray laminography. Appl. Phys. A Mater. Sci. Process. **111**, 983–995 (2013). https://doi.org/10.1007/s00339-013-7687-2

93. C. Gervais, J.J. Boon, F. Marone, E.S.B. Ferreira, Characterization of porosity in a 19th century painting ground by synchrotron radiation X-ray tomography. Appl. Phys. A Mater. Sci. Process. **111**, 31–38 (2013). https://doi.org/10.1007/s00339-012-7533-y

94. K. Krug, L. Porra, P. Coan, A. Wallert, J. Dik, A. Coerdt, A. Bravin, M. Elyyan, P. Reischig, L. Helfen, T. Baumbach, Relics in medieval altarpieces? Combining X-ray tomographic, laminographic and phase-contrast imaging to visualize thin organic objects in paintings. J. Synchrotron Radiat. **15**, 55–61 (2007). https://doi.org/10.1107/S0909049507045438

95. F.T.H. Broers, I. Verslype, K.W. Bossers, F. Vanmeert, V. Gonzalez, J. Garrevoet, A. van Loon, E. van Duijn, A. Krekeler, N. De Keyser, I. Steeman, P. Noble, K. Janssens, F. Meirer, K. Keune, Correlated X-ray fluorescence and ptychographic nanotomography on Rembrandt's The Night Watch reveals unknown lead "layer." Sci. Adv. **9**, eadj9394 (2023). https://doi.org/10.1126/sciadv.adj9394

96. M. Cotte, A. Genty-Vincent, K. Janssens, J. Susini, Applications of synchrotron X-ray nano-probes in the field of cultural heritage. C. R. Phys. **19**, 575–588 (2018). https://doi.org/10.1016/j.crh.y.2018.07.002

97. E. Pouyet, M. Cotte, B. Fayard, M. Salomé, F. Meirer, A. Mehta, E.S. Uffelman, A. Hull, F. Vanmeert, J. Kieffer, M. Burghammer, K. Janssens, F. Sette, J. Mass, 2D X-ray and FTIR micro-analysis of the degradation of cadmium yellow pigment in paintings of Henri Matisse. Appl. Phys. A Mater. Sci. Process. **121**, 967–980 (2015). https://doi.org/10.1007/s00339-015-9239-4

98. J. Mass, J. Sedlmair, C.S. Patterson, D. Carson, B. Buckley, C. Hirschmugl, SR-FTIR imaging of the altered cadmium sulfide yellow paints in Henri Matisse's le Bonheur de vivre (1905–6)-examination of visually distinct degradation regions. Analyst **138**, 6032–6043 (2013). https://doi.org/10.1039/c3an00892d

99. M. Vermeulen, K. Janssens, J. Sanyova, V. Rahemi, C. McGlinchey, K. De Wael, Assessing the stability of arsenic sulfide pigments and influence of the binding media on their degradation by means of spectroscopic and electrochemical techniques. Microchem. J. **138**, 82–91 (2018). https://doi.org/10.1016/j.microc.2018.01.004

100. J.J. Hermans, K. Keune, A. Van Loon, R.W. Corkery, P.D. Iedema, Ionomer-like structure in mature oil paint binding media. RSC Adv. **6**, 93363–93369 (2016). https://doi.org/10.1039/c6ra18267d

101. G. Van Der Snickt, K. Janssens, J. Dik, W. De Nolf, F. Vanmeert, J. Jaroszewicz, M. Cotte, G. Falkenberg, L. Van Der Loeff, Combined use of synchrotron radiation based micro-X-ray fluorescence, micro-X-ray diffraction, micro-X-ray absorption near-edge, and micro-fourier transform infrared spectroscopies for revealing an alternative degradation pathway of the pigment Cadmium Yellow in a Painting by Van Gogh. Anal. Chem. **84**, 10221–10228 (2012). https://doi.org/10.1021/ac3015627

102. L. Monico, L. Cartechini, F. Rosi, A. Chieli, C. Grazia, S. de Meyer, G. Nuyts, F. Vanmeert, K. Janssens, M. Cotte, W. de Nolf, G. Falkenberg, I.C.A. Sandu, E.S. Tveit, J. Mass, R.P. de Freitas, A. Romani, C. Miliani, Probing the chemistry of CdS paints in the Scream by in situ noninvasive spectroscopies and synchrotron radiation x-ray techniques. Sci. Adv. **6**, eaay3514 (2020). https://doi.org/10.1126/sciadv.aay3514

103. H. Tan, H. Tian, J. Verbeeck, L. Monico, K. Janssens, G. Van Tendeloo, Nanoscale investigation of the degradation mechanism of a historical chrome yellow paint by quantitative electron energy loss spectroscopy mapping of chromium species. Angewandte Chemie – Int. Ed. **52**, 11360–11363 (2013). https://doi.org/10.1002/anie.201305753

104. R. Punis, M. Veronese, M. Meneghetti, A. Zoleo, Copper soaps formation in verdigris-linseed oil painting mixtures: a multispectroscopic characterization. Inorg. Chem. **63**, 4108–4119 (2024). https://doi.org/10.1021/acs.inorgchem.3c03794

105. R. Punis, A. Zoleo, Cu(II)-binder complexes in azurite and malachite pictorial mixtures: an EPR study. Microchem. J. **200**, 110303 (2024). https://doi.org/10.1016/j.microc.2024.110303

106. L. Monico, K. Janssens, M. Cotte, L. Sorace, F. Vanmeert, B.G. Brunetti, C. Miliani, Chromium speciation methods and infrared spectroscopy for studying the chemical reactivity of lead chromate-based pigments in oil medium. Microchem. J. **124**, 272–282 (2016). https://doi.org/10.1016/j.microc.2015.08.028

107. L. Monico, L. Sorace, M. Cotte, W. De Nolf, K. Janssens, A. Romani, C. Miliani, Disclosing the binding medium effects and the pigment solubility in the (photo)reduction process of chrome yellows
(PbCrO₄/PbCr₁-xSxO₄). ACS Omega **4**, 6607–6619 (2019). https://doi.org/10.1021/acsomega.8b03669

108. L. Monico, K. Janssens, E. Hendriks, F. Vanmeert, G. Van der Snickt, M. Cotte, G. Falkenberg, B.G. Brunetti, C. Miliani, Evidence for degradation of the chrome yellows in Van Gogh's Sunflowers: a study using noninvasive in situ methods and synchrotron-radiation-based X-ray techniques. Angewandte Chemie - Int. Ed. **54**, 13923–13927 (2015). https://doi.org/10.1002/anie.201505840

109. F. Vanmeert, E. Hendriks, G. Van der Snickt, L. Monico, J. Dik, K. Janssens, Chemical mapping by macroscopic X-ray powder diffraction (MA-XRPD) of Van Gogh's Sunflowers: identification of areas with higher degradation risk. Angewandte Chemie - Int. Ed. **57**, 7418–7422 (2018). https://doi.org/10.1002/anie.201713293

110. C. Cucci, J.K. Delaney, M. Picollo, Reflectance hyperspectral imaging for investigation of works of art: old master paintings and illuminated manuscripts. Acc. Chem. Res. **49**, 2070–2079 (2016). https://doi.org/10.1021/acs.accounts.6b00048

111. M. Picollo, C. Cucci, A. Casini, L. Stefani, Hyper-spectral imaging technique in the cultural heritage field: new possible scenarios. Sensors **20**, 2843 (2020). https://doi.org/10.3390/s20102843

112. F. Vanmeert, S. De Meyer, A. Gestels, E.A. Clerici, N. Deleu, S. Legrand, P. Van Espen, G. Van der Snickt, M. Alfeld, J. Dik, L. Monico, W. De Nolf, M. Cotte, V. Gonzalez, S. Saverwyns, L. Depuydt-Elbaum, K. Janssens, Non-invasive and Non-destructive Examination of Artists' Pigments, Paints and Paintings by Means of X-Ray Imaging Methods, in: Analytical Chemistry for the Study of Paintings and the Detection of Forgeries. Cultural Heritage Science, eds. By M.P. Colombini, I. Degano, A. Nevin (Springer, Cham., 2022), pp. 317–357. https://doi.org/10.1007/978-3-030-86865-9_11

113. B. Brunetti, C. Miliani, F. Rosi, B. Doherty, L. Monico, A. Romani, A. Sgamellotti, Non-invasive investigations of paintings by portable instrumentation: the MOLAB experience. Top. Curr. Chem. **374**, 10 (2016). https://doi.org/10.1007/s41061-015-0008-9

114. F. Rosi, L. Cartechini, D. Sali, C. Miliani, Recent trends in the application of Fourier Transform Infrared (FT-IR) spectroscopy in heritage science: from micro- to non-invasive FT-IR. Phys. Sci. Rev. **4**, 20180006 (2019). https://doi.org/10.1515/psr-2018-0006

115. S. Legrand, F. Vanmeert, G. Van der Snickt, M. Alfeld, W. De Nolf, J. Dik, K. Janssens, Examination of historical paintings by state-of-the-art hyperspectral imaging methods: from scanning infrared spectroscopy to computed X-ray laminography. Herit. Sci. **2**, 13 (2014). https://doi.org/10.1186/2050-7445-2-13

116. M. Alfeld, L. de Viguerie, Recent developments in spectroscopic imaging techniques for historical paintings—a review. Spectrochim. Acta Part B At. Spectrosc. **136**, 81–105 (2017). https://doi.org/10.1016/j.sab.2017.08.003

117. S. Mosca, C. Conti, N. Stone, P. Matousek, Spatially offset Raman spectroscopy. Nat. Rev. Methods Primers **1**, 21 (2021). https://doi.org/10.1038/s43586-021-00019-0

118. J. Striova, A.D. Fovo, R. Fontana, Reflectance imaging spectroscopy in heritage science. Rivista Del Nuovo Cimento **43**, 515–566 (2020). https://doi.org/10.1007/s40766-020-00011-6

119. P. Matousek, C. Conti, M. Realini, C. Colombo, Micro-scale spatially offset Raman spectroscopy for non-invasive subsurface analysis of turbid materials. Analyst **141**, 731–739 (2016). https://doi.org/10.1039/c5an02129d

120. L. Bertrand, S. Schöder, D. Anglos, M.B.H. Breese, K. Janssens, M. Moini, A. Simon, Mitigation strategies for radiation damage in the analysis of ancient materials. TrAC - Trends Anal. Chem. **66**, 128–145 (2015). https://doi.org/10.1016/j.trac.2014.10.005

121. L. Bertrand, S. Schöder, I. Joosten, S.M. Webb, M. Thoury, T. Calligaro, É. Anheim, A. Simon, Practical advances towards safer analysis of heritage samples and objects. TrAC - Trends Anal. Chem. **164**, 117078 (2023). https://doi.org/10.1016/j.trac.2023.117078

122. C.G. Schroer, P. Boye, J.M. Feldkamp, J. Patommel, D. Samberg, A. Schropp, A. Schwab, S. Stephan, G. Falkenberg, G. Wellenreuther, N. Reimers, Hard X-ray nanoprobe at beamline P06 at PETRA III. Nucl. Instrum. Methods Phys. Res. **A** **616**, 93–97 (2010). https://doi.org/10.1016/j.nima.2009.10.094

123. L. Monico, K. Janssens, M. Alfeld, M. Cotte, F. Vanmeert, C.G. Ryan, G. Falkenberg, D.L. Howard, B.G. Brunetti, C. Miliani, Full spectral XANES imaging using the Maia detector array as a new tool for the study of the alteration process of chrome yellow pigments in paintings by Vincent van Gogh. J. Anal. At. Spectrom. **30**, 613–626 (2015). https://doi.org/10.1039/c4ja00419a

124. S. Mayda, L. Monico, D. Krishnan, S. De Meyer, M. Cotte, J. Garrevoet, G. Falkenberg, I.C. Sandu, B. Partoens, D. Lamoen, A. Romani, C. Miliani, J. Verbeeck, K. Janssens, A combined experimental and
computational approach to understanding CdS pigment oxidation in a renowned early 20th century
painting. Chem. Mater. **35**, 10403–10415 (2023). https://doi.org/10.1021/acs.chemmater.3c01470

125. L. Monico, A. Chieli, S. De Meyer, M. Cotte, W. de Nolf, G. Falkenberg, K. Janssens, A. Romani, C. Miliani, Role of the relative humidity and the Cd/Zn stoichiometry in the photooxidation process of cadmium yellows (CdS/Cd₁-xZnₓS) in oil paintings. Chem. Eur. J. **24**, 11584–11593 (2018). https://doi.org/10.1002/chem.201801503

126. J. Salvant, J. Williams, M. Ganio, F. Casadio, C. Daher, K. Sutherland, L. Monico, F. Vanmeert, S. De Meyer, K. Janssens, C. Cartwright, M. Walton, A roman egyptian painting workshop: technical investigation of the portraits from tebtunis, Egypt. Archaeometry **60**, 815–833 (2018). https://doi.org/10.1111/arcm.12351

127. N. De Keyser, F.T.H. Broers, F. Vanmeert, A. van Loon, F. Gabrieli, S. De Meyer, A. Gestels, V. Gonzalez, E. Hermens, P. Noble, F. Meirer, K. Keune, K. Janssens, Discovery of pararealgar and semi-amorphous pararealgar in Rembrandt's The Night Watch: analytical study and historical con-textualization. Herit Sci **12**, 237 (2024). https://doi.org/10.1186/s40494-024-01350-x

128. S. De Meyer, F. Vanmeert, R. Vertongen, A. Van Loon, V. Gonzalez, J. Delaney, K. Dooley, J. Dik, G. Van der Snickt, A. Vandivere, K. Janssens, Macroscopic X-ray powder diffraction imaging reveals Vermeer's discriminating use of lead white pigments in Girl with a Pearl Earring. Sci. Adv. **5**, eaax1975 (2019). https://doi.org/10.1126/sciadv.aax1975

129. A. van Loon, A. Vandivere, J.K. Delaney, K.A. Dooley, S. De Meyer, F. Vanmeert, V. Gonzalez, K. Janssens, E. Leonhardt, R. Haswell, S. de Groot, P. D’Imporzano, G.R. Davies, Beauty is skin deep: the skin tones of Vermeer’s Girl with a Pearl Earring. Herit. Sci. **7**, 102 (2019). https://doi.org/10.1186/s40494-019-0344-0

130. K. Janssens, S. Legrand, G. Van Der Snickt, F. Vanmeert, Virtual archaeology of altered paintings: multiscale chemical imaging tools. Elements **12**, 39–44 (2016). https://doi.org/10.2113/gselements.12.1.39

131. W. De Nolf, F. Vanmeert, K. Janssens, XRDUA: Crystalline phase distribution maps by two-dimensional scanning and tomographic (micro) X-ray powder diffraction. J. Appl. Crystallogr. **47**, 1107–1117 (2014). https://doi.org/10.1107/S1600576714008218

132. L. Monico, M. Cotte, F. Vanmeert, L. Amidani, K. Janssens, G. Nuyts, J. Garrevoet, G. Falkenberg, P. Glatzel, A. Romani, C. Miliani, Damages induced by synchrotron radiation-based X-ray microanalysis in chrome yellow paints and related Cr-compounds: assessment, quantification, and mitigation strategies. Anal. Chem. **92**, 14164–14173 (2020). https://doi.org/10.1021/acs.analchem.0c03251

133. C. Riekel, M. Burghammer, R. Davies, Progress in micro- and nano-diffraction at the ESRF ID13 beamline. IOP Conf. Ser. Mater. Sci. Eng. **14**, 012013 (2010). https://doi.org/10.1088/1757-899x/14/1/012013

134. G. Pastorelli, A.S.O. Miranda, E.A. Clerici, P. d’Imporzano, B.V. Hansen, K. Janssens, G.R. Davies, N. Borring, Darkening of lead white in old master drawings and historic prints: a multi-analytical investigation. Microchem. J. **199**, 109912 (2024). https://doi.org/10.1016/j.microc.2024.109912

135. M. Gomez Lobon, M. Ghirardello, E. Juncosa Darder, C. Palomino Cabello, M. Bauza, M. Cotte, A. Burnstock, A. Nevin, S.R. Amato, F.C. Izzo, D. Comelli, A study of cadmium yellow paints from Joan Miró’s paintings and studio materials preserved at the Fundació Miró Mallorca. Herit. Sci. **11**, 145 (2023). https://doi.org/10.1186/s40494-023-00987-4

136. A. Suzuki, C.S. Cheung, Y. Li, A. Hogg, P.S. Atkinson, C. Riminesi, C. Miliani, H. Liang, Time and spatially resolved vis-NIR hyperspectral imaging as a novel monitoring tool for laser-based spectroscopy to mitigate radiation damage on paintings. Analyst **149**, 2338–2350 (2024). https://doi.org/10.1039/d3an02041j

137. M. Cotte, E. Checroun, W. De Nolf, Y. Taniguchi, L. De Viguerie, M. Burghammer, P. Walter, C. Rivard, M. Salomé, K. Janssens, J. Susini, Lead soaps in paintings: friends or foes? Stud. Conserv. **62**, 2–23 (2017). https://doi.org/10.1080/00393630.2016.1232529

138. E.H. Purdy, S. Critchley, C. Holé, M. Cotte, A. Kirkham, M. Casford, Characterisation of rouaite, an unusual copper-containing pigment in early modern English wall paintings, by synchrotron micro X-Ray diffraction and micro X-Ray absorption spectroscopy. Appl. Phys. A Mater. Sci. Process. **130**, 817 (2024). https://doi.org/10.1007/s00339-024-07954-1

139. V. Gonzalez, G. Wallez, E. Ravaud, M. Eveno, I. Fazlic, T. Fabris, A. Nevin, T. Calligaro, M. Menu, V. Delieuvin, M. Cotte, X-ray and infrared microanalyses of Mona Lisa’s ground layer and significance regarding Leonardo da Vinci’s Palette. J. Am. Chem. Soc. **145**, 23205–23213 (2023). https://doi.org/10.1021/jacs.3c07000
140. V. Gonzalez, M. Cotte, G. Wallez, A. van Loon, W. de Nolf, M. Eveno, K. Keune, P. Noble, J. Dik, Unraveling the Composition of Rembrandt's Impasto through the Identification of Unusual Plumbonacrite by Multimodal X-ray Diffraction Analysis. Angewandte Chemie – Int. Ed. **58**, 5619–5622 (2019). https://doi.org/10.1002/anie.201813105

141. M. Cotte, E. Pouyet, M. Salomé, C. Rivard, W. De Nolf, H. Castillo-Michel, T. Fabris, L. Monico, K. Janssens, T. Wang, P. Sciau, L. Verger, L. Cormier, O. Dargaud, E. Brun, D. Bugnazet, B. Fayard, B. Hesse, A.E. Pradas Del Real, G. Veronesi, J. Langlois, N. Balcar, Y. Vandenberghe, V.A. Solé, J. Kieffer, R. Barrett, C. Cohen, C. Cornu, R. Baker, E. Gagliardini, E. Papillon, J. Susini, The ID21 X-ray and infrared microscopy beamline at the ESRF: Status and recent applications to artistic materials. J. Anal. At. Spectrom. **32**, 477–493 (2017). https://doi.org/10.1039/c6ja00356g

142. L. Monico, K. Janssens, F. Vanmeert, M. Cotte, B.G. Brunetti, G. Van Der Snickt, M. Leeuwestein, J. Salvant Plisson, M. Menu, C. Miliani, Degradation process of lead chromate in paintings by Vincent van Gogh studied by means of spectromicroscopic methods. Part 5. Effects of nonoriginal surface coatings into the nature and distribution of chromium and sulfur species in chrome yellow paints. Anal. Chem. **86**, 10804–10811 (2014). https://doi.org/10.1021/ac502841g

143. L. Monico, K. Janssens, M. Cotte, A. Romani, L. Sorace, C. Grazia, B.G. Brunetti, C. Miliani, Synchrotron-based X-ray spectromicroscopy and electron paramagnetic resonance spectroscopy to investigate the redox properties of lead chromate pigments under the effect of visible light. J. Anal. At. Spectrom. **30**, 1500–1510 (2015). https://doi.org/10.1039/c5ja00091b

144. V. Otero, M. Vilarigues, L. Carlyle, M. Cotte, W. De Nolf, M.J. Melo, A: Little key to oxalate formation in oil paints: protective patina or chemical reactor? Photochem. Photobiol. Sci. **17**, 266–270 (2018). https://doi.org/10.1039/c7pp00307b

145. L. Monico, F. d'Acapito, M. Cotte, K. Janssens, A. Romani, G. Ricci, C. Miliani, L. Cartechini, Total electron yield (TEY) detection mode Cr K-edge XANES spectroscopy as a direct method to probe the composition of the surface of darkened chrome yellow (PbCr<sub>1-x</sub>S<sub>x</sub>O<sub>4</sub>) and potassium chromate paints. Nucl. Instrum. Methods Phys. Res. B **539**, 141–147 (2023). https://doi.org/10.1016/j.nimb.2023.03.040

146. M. Radepont, Y. Coquinot, K. Janssens, J.J. Ezrati, W. De Nolf, M. Cotte, Thermodynamic and experimental study of the degradation of the red pigment mercury sulfide. J. Anal. At. Spectrom. **30**, 599–612 (2015). https://doi.org/10.1039/c4ja00372a

147. A.A. Gambardella, C.M. Schmidt Patterson, S.M. Webb, M.S. Walton, Sulfur K-edge XANES of lazurite: toward determining the provenance of lapis lazuli. Microchem. J. **125**, 299–307 (2016). https://doi.org/10.1016/j.microc.2015.11.030

148. A.A. Gambardella, M. Cotte, W. de Nolf, K. Schnetz, R. Erdmann, R. van Elsas, V. Gonzalez, A. Wallert, P.D. Iedema, M. Eveno, K. Keune, Sulfur K-edge micro- and full-field XANES identify marker for preparation method of ultramarine pigment from lapis lazuli in historical paints. Sci. Adv. **6**, eaay8782 (2020). https://doi.org/10.1126/sciadv.aay8782

149. L. Monico, F. Rosi, R. Vivani, L. Cartechini, K. Janssens, N. Gauquelin, D. Chezganov, J. Verbeeck, M. Cotte, F. d'Acapito, L. Barni, C. Grazia, L. Pensabene Buemi, J.L. Andral, C. Miliani, A. Romani, Deeper insights into the photoluminescence properties and (photo)chemical reactivity of cadmium red (CdS<sub>1-x</sub>S<sub>x</sub>Se<sub>2</sub>) paints in renowned twentieth century paintings by state-of-the-art investigations at multiple length scales. Eur Phys J Plus **137**, 311 (2022). https://doi.org/10.1140/epjp/s13360-022-02447-7

150. A. Kostomitsopoulou Marketou, F. Giannici, S. Handberg, W. De Nolf, M. Cotte, F. Caruso, Synchrotron radiation-based micro-XANES and Micro-XRF study of unsuccessfully produced egyptian blue from the late hellenistic production site of Kos (Dodecanese, Greece). Anal. Chem. **93**, 11557–11567 (2021). https://doi.org/10.1021/acs.analchem.1c02063

151. V. Otero, J.V. Pinto, L. Carlyle, M. Vilarigues, M. Cotte, M.J. Melo, Nineteenth century chrome yellow and chrome deep from Winsor & NewtonTM. Stud. Conserv. **62**, 123–149 (2017). https://doi.org/10.1080/00393630.2015.1131478

152. G. Martinez-Criado, J. Villanova, R. Tucoulou, D. Salomon, J.P. Suuronen, S. Laboure, C. Guilloud, V. Valls, R. Barrett, E. Gagliardini, Y. Dabin, R. Baker, S. Bohic, C. Cohen, J. Morse, ID16B: A hard X-ray nanoprobe beamline at the ESRF for nano-analysis. J. Synchrotron Radiat. **23**, 344–352 (2016). https://doi.org/10.1107/S1600577515019839

153. E. Avranovich Clerici, S. De Meyer, G. Van der Snickt, K. Janssens, Synchrotron X-ray powder diffraction study of lead white oxidation by sodium hypochlorite, in: Acta Artis Academica, eds. By J. Hradilová, D. Hradil (Academy of Fine Arts Prague, Prague, 2017), pp. 13–20.
154. N. Salvadó, S. Butí, M.A.G. Aranda, T. Pradell, New insights on blue pigments used in 15th century paintings by synchrotron radiation-based micro-FTIR and XRD. *Anal. Methods* **6**, 3610–3621 (2014). https://doi.org/10.1039/c4ay00424h

155. A. Fitch, C. Dejoie, E. Covacci, G. Confalonieri, O. Grendal, L. Claustre, P. Guillou, J. Kieffer, W. De Nolf, S. Petitdemange, M. Ruat, Y. Watier, ID22 - the high-resolution powder-diffraction beamline at ESRF. *J. Synchrotron Radiat.* **30**, 1003–1012 (2023). https://doi.org/10.1107/S1600577523004915

156. V. Gonzalez, D. Gourier, T. Calligaro, K. Toussaint, G. Wallez, M. Menu, Revealing the origin and history of lead-white pigments by their photoluminescence properties. *Anal. Chem.* **89**, 2909–2918 (2017). https://doi.org/10.1021/acs.analchem.6b04195

157. A. Fanost, A. Gimat, L. de Viguerie, P. Martinetto, A.C. Giot, M. Clémancey, G. Blondin, F. Gaslain, H. Glanville, P. Walter, G. Mériguet, A.L. Rollet, M. Jaber, Revisiting the identification of commercial and historical green earth pigments. *Colloids. Surf. A Physicochem. Eng. Asp.* **584**, 124035 (2020). https://doi.org/10.1016/j.colsurfa.2019.124035

158. V. Gonzalez, G. Wallez, T. Calligaro, D. Gourier, M. Menu, Synthesizing lead white pigments by lead corrosion: new insights into the ancient manufacturing processes. *Corros. Sci.* **146**, 10–17 (2019). https://doi.org/10.1016/j.corsci.2018.10.033

159. G.A. Chahine, N. Blanc, S. Arnaud, F. De Geuser, R. Guinebretière, N. Boudet, Advanced non-destructive in situ characterization of metals with the French collaborating research group D2AM/BM02 beamline at the European synchrotron radiation facility. *Metals* (Basel) **9**, 352 (2019). https://doi.org/10.3390/met9030352

160. M. Sánchez del Río, J. García-Rivas, M. Suárez, E. García-Romero, Crystal–chemical and diffraction analyses of Maya blue suggesting a different provenance of the palygorskite found in Aztec pigments*. *Archaeometry* **63**, 738–752 (2021). https://doi.org/10.1111/arcm.12644

161. F.J. Martínez-Casado, M. Ramos-Riesco, J.A. Rodríguez-Cheda, M.I. Redondo-Yélamos, L. Garrido, A. Fernández-Martínez, J. García-Barriocanal, I. Da Silva, M. Durán-Olivencia, A. Poulain, Lead(II) soaps: Crystal structures, polymorphism, and solid and liquid mesophases. *Phys. Chem. Chem. Phys.* **19**, 17009–17018 (2017). https://doi.org/10.1039/c7cp02351k

162. F. D'Acapito, G.O. Lepore, A. Puri, A. Laloni, F. La Manna, E. Dettona, A. De Luisa, A. Martin, The LISA beamline at ESRF. *J. Synchrotron Radiat.* **26**, 551–558 (2019). https://doi.org/10.1107/S160057751801843X

163. J.F.W. Mosselmans, P.D. Quinn, A.J. Dent, S.A. Cavill, S.D. Moreno, A. Peach, P.J. Leicester, S.J. Keylock, S.R. Gregory, K.D. Atkinson, J.R. Rosell, I18—The microfocus spectroscopy beamline at the Diamond Light Source. *J. Synchrotron Radiat.* **16**, 818–824 (2009). https://doi.org/10.1107/S0909049509032282

164. S.W.T. Price, A. Van Loon, K. Keune, A.D. Parsons, C. Murray, A.M. Beale, J.F.W. Mosselmans, Unravelling the spatial dependency of the complex solid-state chemistry of Pb in a paint micro-sample from Rembrandt's Homer using XRD-CT. *Chem. Commun.* **55**, 1931–1934 (2019). https://doi.org/10.1039/c8cc09705d

165. S.P. Thompson, J.E. Parker, J. Potter, T.P. Hill, A. Birt, T.M. Cobb, F. Yuan, C.C. Tang, Beamline I11 at Diamond: a new instrument for high resolution powder diffraction. *Rev. Sci. Instrum.* **80**, 075107 (2009). https://doi.org/10.1063/1.3167217

166. S. Bette, R.K. Kremer, G. Eggert, C.C. Tang, R.E. Dinnebier, On verdigris, part I: synthesis, crystal structure solution and characterisation of the 1–2–0 phase ($Cu_3(CH_3COO)_2(OH)_4$). *Dalton Trans.* **46**, 14847–14858 (2017). https://doi.org/10.1039/c7dt03288a

167. S. Bette, A. Costes, R.K. Kremer, G. Eggert, C.C. Tang, R.E. Dinnebier, On verdigris, part III: crystal structure, magnetic and spectral properties of anhydrous copper(II) acetate, a paddle wheel Chain. *Z. Anorg. Allg. Chem.* **645**, 988–997 (2019). https://doi.org/10.1002/zaac.201900125

168. A.J. Dent, G. Cibin, S. Ramos, S.A. Parry, D. Gianolio, A.D. Smith, S.M. Scott, L. Varandas, S. Patel, M.R. Pearson, L. Hudson, N.A. Krumpa, A.S. Marsch, P.E. Robbins, Performance of B18, the core EXAFS bending magnet beamline at diamond. *J. Phys. Conf. Ser.* **430**, 012023 (2013). https://doi.org/10.1088/1742-6596/430/1/012023

169. J. Juanhuix, F. Gil-Ortiz, G. Cuní, C. Coldelram, J. Nicolás, J. Lidón, E. Boter, C. Ruget, S. Ferrer, J. Benach, Developments in optics and performance at BL13-XALOC, the macromolecular crystallography beamline at the Alba Synchrotron. *J. Synchrotron Radiat.* **21**, 679–689 (2014). https://doi.org/10.1107/S160057751400825X
170. N. Salvadó, S. Butí, C. Clemente, V. Beltran, G. Cinque, J. Juanhuix, T. Pradell, Microanalytical study of luster glazed gilding and silvering from Baroque altarpieces. Pure Appl. Chem. **90**, 477–492 (2018). https://doi.org/10.1515/pac-2017-0602

171. L. Rebuffi, J.R. Plaisier, M. Abdellatief, A. Lausi, A.P. Scardi, Mcx: a synchrotron radiation beamline for X-ray diffraction line profile analysis. Z. Anorg. Allg. Chem. **640**, 3100–3106 (2014). https://doi.org/10.1002/zaac.201400163

172. E. Possenti, C. Colombo, C. Conti, L. Gigli, M. Merlini, J.R. Plaisier, M. Realini, G.D. Gatta, What's underneath? A non-destructive depth profile of painted stratigraphies by synchrotron grazing incidence X-ray diffraction. Analyst **143**, 4290–4297 (2018). https://doi.org/10.1039/c8an000901e

173. L. Bertrand, M.A. Languille, S.X. Cohen, L. Robinet, C. Gervais, S. Leroy, D. Bernard, E. Le Pennec, W. Josse, J. Doucet, S. Schöder, European research platform IPANEMA at the SOLEIL synchrotron for ancient and historical materials. J. Synchrotron Radiat. **18**, 765–772 (2011). https://doi.org/10.1107/S090904951102334X

174. S. Schöder, K. Müller, L. Tranchant, A. Rouquié, P. Gueriau, M. Thoury, E. Bérard, T. Okbinoglu, F. Berenguer, C. Iacconi, L. Robbiola, T. Moreno, S.X. Cohen, L. Bertrand, Heritage research at the PUMA beamline. Appl. Phys. A Mater. Sci. Process. **130**, 848 (2024). https://doi.org/10.1007/s0339-024-08026-0

175. M. Eveno, E. Ravaud, Early occurrences of the use of smalt and shell gold in the Madonna of Humility by Jacopo Bellini at the beginning of the fifteenth century. Eur. Phys. J. Plus **136**, 685 (2021). https://doi.org/10.1140/epjp/s13360-021-01650-2

176. M. Godet, L. Binet, S. Schöder, L. Brunel-Duverger, M. Thoury, L. Bertrand, X-ray irradiation effects on Egyptian blue and green pigments. J. Anal. At. Spectrom. **37**, 1265–1272 (2022). https://doi.org/10.1039/d2ja00020b

177. C. Barata, F. Rocha, A.J. Cruz, S. Andrejkovičová, S. Reguer, Synchrotron X-ray diffraction of bole layers from Portuguese gilded baroque retables. Appl. Clay Sci. **116–117**, 39–45 (2015). https://doi.org/10.1016/j.clay.2015.08.012

178. C. Santoro, K. Zarkout, A.S. Le Hô, F. Mirambet, D. Gourier, L. Binet, S. Pagès-Camagna, S. Reguer, S. Mirabaud, Y. Le Du, P. Griesmar, N. Lubin-Germain, M. Menu, New highlights on degradation process of verdigris from easel paintings. Appl. Phys. A Mater. Sci. Process. **114**, 637–645 (2014). https://doi.org/10.1007/s00339-014-8253-2

179. C. Gervais, M. Thoury, S. Réguer, P. Gueriau, J. Mass, Radiation damages during synchrotron X-ray micro-analyses of Prussian blue and zinc white historic paintings: detection, mitigation and integration. Appl. Phys. A Mater. Sci. Process. **121**, 949–955 (2015). https://doi.org/10.1007/s00339-015-9462-z

180. F. Baudelet, Q. Kong, L. Nataf, J.D. Cafun, A. Congeduti, A. Monza, S. Chagnot, J.P. Itié, ODE: a new beam line for high-pressure XAS and XMCD studies at SOLEIL. High Press Res. **31**, 136–139 (2011). https://doi.org/10.1080/08957959.2010.532794

181. C. Gervais, M.A. Languille, G. Moretti, S. Réguer, X-ray photochemistry of prussian blue cellulosic materials: evidence for a substrate-mediated redox process. Langmuir **31**, 8168–8175 (2015). https://doi.org/10.1021/acs.langmuir.5b00770

182. N.P. Edwards, S.M. Webb, U. Bergmann, Photons, folios, and fossils: the X-ray imaging and spectroscopy program of ancient materials at SSRL. Synchrotron Radiat. News **32**, 22–28 (2019). https://doi.org/10.1080/08940886.2019.1680211

183. F.T.H. Broers, K. Janssens, J. Nelson Weker, S.M. Webb, A. Mehta, F. Meirer, K. Keune, Two pathways for the degradation of orpiment pigment (As₂S₃) found in paintings. J. Am. Chem. Soc. **145**, 8847–8859 (2023). https://doi.org/10.1021/jacs.2c12271

184. M. Vermeulen, S.M. Webb, S. Russick, A.C. McGeachy, K. Muratore, M.S. Walton, Identification, transformations and mobility of hazardous arsenic-based pigments on 19th century bookbindings in accessible library collections. J. Hazard. Mater. **454**, 131453 (2023). https://doi.org/10.1016/j.jhazmat.2023.131453

185. M. Ganio, E.S. Pouyet, S.M. Webb, C.M. Schmidt Patterson, M.S. Walton, From lapis lazuli to ultramarine blue: Investigating Cennino Cennini’s recipe using sulfur K-edge XANES. Pure Appl. Chem. **90**, 463–475 (2018). https://doi.org/10.1515/pac-2017-0502

186. Y. Gao, A. Kiss, R. Tappero, B. Stripe, W. Yun, Y.S. Chu, Design optimization of a confocal X-ray fluorescence imaging capability for XFM and SRX at NSLS-II. Proceedings Volume 11112, Proc. SPIE 11112, X-Ray Nanoimaging: Instruments and Methods IV, 1111204 (9 September 2019). https://doi.org/10.1117/12.2528026
187. M. Porell, M. Cushman, J.S.T. Fischel, M.H.H. Fischel, D.L. Sparks, R. Grayburn, Scanning X-ray fluorescence spectroscopy and micro-X-ray absorption near-edge structure analysis as a guiding tool for the conservation treatment of two eighteenth-century Philadelphian portraits. X-Ray Spectrom. **53**, 232–241 (2024). https://doi.org/10.1002/xrs.3345

188. J. Zhu, Zhang, G. Chen, J. Du, W. Li, Y. Li, The application of confocal depth-resolved micro-X-ray absorption spectroscopy to study colorant copper in ancient lead-silica glassy system at the Beijing Synchrotron Radiation Facility. Optik **218**, 165239 (2020). https://doi.org/10.1016/j.ijleo.2020.165239

189. L. Shen, C. Wang, J. Zhang, B. Cui, S. Zhu, J. Mao, Cu and As containing pigments in Zhejiang architecture polychrome paintings: a case study of degradation products of emerald green. Herit. Sci. **11**, 9 (2023). https://doi.org/10.1186/s40494-022-00834-y

190. D.L. Howard, M.D.D. Jonge, N. Afshar, C.G. Ryan, R. Kirkham, J. Reinhardt, C.M. Kewish, J. McKinlay, A. Walsh, J. Divitcos, N. Basten, L. Adamson, T. Fiala, L. Sammut, D.J. Paterson, The XFM beamline at the Australian Synchrotron. J. Synchrotron Radiat. **27**, 1447–1458 (2020). https://doi.org/10.1107/S1600577520010152

191. M. Cotte, J. Susini, J. Dik, K. Janssens, Synchrotron-based X-ray absorption spectroscopy for art conservation: looking back and looking forward. Acc. Chem. Res. **43**, 705–714 (2010). https://doi.org/10.1021/ar900199m

192. F. D'Acapito, X-Ray Absorption Spectroscopy (XAS) Applied to Cultural Heritage, in: Handbook of Cultural Heritage Analysis (Springer, 2022), pp. 45–67. https://doi.org/10.1007/978-3-030-6001-6-7_4

193. K. Janssens, M. Cotte, The use of XAS and related methods in cultural heritage investigations. Int. Tables Crystallogr. **1**, 1039–1046 (2024). https://doi.org/10.1107/S1574870720004802

194. M.E. Fleet, X. Liu, X-ray absorption spectroscopy of ultramarine pigments: a new analytical method for the polysulfide radical anion S<sub>3</sub><sup>-</sup> chromophore. Spectrochim. Acta Part B At. Spectrosc. **65**, 75–79 (2010). https://doi.org/10.1016/j.sab.2009.11.008

195. S. Hageraats, M. Thoury, M. Cotte, L. Bertrand, K. Janssens, K. Keune, Microchemical Imaging of Oil Paint Composition and Degradation: State-of-the-Art and Future Prospects, in: Analytical Chemistry for the Study of Paintings and the Detection of Forgeries. Cultural Heritage Science, eds. By M.P. Colombini, I. Degano, A. Nevin (Springer, Cham., 2022), pp. 359–418. https://doi.org/10.1007/978-3-030-86865-9_12

196. M. Siegbahn, The Spectroscopy of X-rays, vol. 10 (Humphrey Milford, Oxford University Press, Oxford, 1925)

197. E. Prince, Mathematical, physical and chemical tables. Int. Tables Crystallogr. (2021). https://doi.org/10.1107/97809553602060000117

198. W.T. Elam, B.D. Ravel, J.R. Sieber, A new atomic database for X-ray spectroscopic calculations. Radiat. Phys. Chem. **63**, 121–128 (2002). https://doi.org/10.1016/S0969-806X(01)00227-4

199. T. Schoonjans, A. Brunetti, B. Golosio, M. Sanchez Del Rio, V.A. Solé, C. Ferrero, L. Vincze, The xraylib library for X-ray-matter interactions. Recent developments. Spectrochim. Acta Part B At. Spectrosc. **66**, 776–784 (2011). https://doi.org/10.1016/j.sab.2011.09.011

200. B. Ravel, ATOMS: Crystallography for the X-ray absorption spectroscopist. J. Synchrotron Radiat. **8**, 314–316 (2001). https://doi.org/10.1107/S090904950001493X

201. M. Newville, Larch: An analysis package for XAFS and related spectroscopies. J. Phys. Conf. Ser. **430**, 012007 (2013). https://doi.org/10.1088/1742-6596/430/1/012007

202. P.A. Lee, P.H. Citrin, P. Eisenberger, B.M. Kincaid, Extended X-ray absorption fine structure its strengths and limitations as a structural tool. Rev. Mod. Phys. **53**, 769–806 (1981). https://doi.org/10.1103/RevModPhys.53.769

203. J.J. Rehr, R.C. Albers, Theoretical approaches to X-ray absorption fine structure. Rev. Mod. Phys. **72**, 621–654 (2000). https://doi.org/10.1103/RevModPhys.72.621

204. C.A. Ashley, S. Doniach, Theory of extended X-ray absorption edge fine structure (EXAFS) in crystalline solids. Phys. Rev. B **11**, 1279–1288 (1975). https://doi.org/10.1103/PhysRevB.11.1279

205. C.R. Natoli, M. Benfatto, A unifying scheme of interpretation of X-ray absorption spectra based on the multiple scattering theory. Le Journal de Physique Colloques **47**, C8-11-C8-23 (1986). https://doi.org/10.1051/jphyscol:1986802

206. A. Pantelouris, H. Modrow, M. Pantelouris, J. Hormes, D. Reinen, The influence of coordination geometry and valency on the K-edge absorption near edge spectra of selected chromium compounds. Chem. Phys. **300**, 13–22 (2004). https://doi.org/10.1016/j.chemphys.2003.12.017
207. M. Wilke, F. Farges, P.E. Petit, G.E. Brown, F. Martin, Oxidation state and coordination of Fe in minerals: an Fe K-XANES spectroscopic study. Am. Miner. **86**, 714–730 (2001). https://doi.org/10.2138/am-2001-5-612

208. A. Snigirev, I. Snigireva, High energy X-ray micro-optics. C. R. Phys. **9**, 507–516 (2008). https://doi.org/10.1016/j.crhy.2008.02.003

209. P. Kirkpatrick, A.V. Baez, Formation of optical images by X-rays. J. Opt. Soc. Am. **38**, 766–774 (1948). https://doi.org/10.1364/JOSA.38.000766

210. D.X. Balaic, K.A. Nugent, Z. Barnea, R. Garrett, S.W. Wilkins, Focusing of X-rays by total external reflection from a paraboloidally tapered glass capillary. J. Synchrotron Radiat. **2**, 296–299 (1995). https://doi.org/10.1107/s0909049595010831

211. Y.S. Chu, J.M. Yi, F. De Carlo, Q. Shen, W.K. Lee, H.J. Wu, C.L. Wang, J.Y. Wang, C.J. Liu, C.H. Wang, S.R. Wu, C.C. Chien, Y. Hwu, A. Tkachuk, W. Yun, M. Feser, K.S. Liang, C.S. Yang, J.H. Je, G. Margaritondo, Hard-x-ray microscopy with Fresnel zone plates reaches 40 nm Rayleigh resolution. Appl. Phys. Lett. **92**, 103119 (2008). https://doi.org/10.1063/1.2857476

212. H.C. Kang, H. Yan, R.P. Winarski, M.V. Holt, J. Maser, C. Liu, R. Conley, S. Vogt, A.T. MacRander, G.B. Stephenson, Focusing of hard x-rays to 16 nanometers with a multilayer Laue lens. Appl. Phys. Lett. **92**, 221114 (2008). https://doi.org/10.1063/1.2912503

213. A. Snigirev, V. Kohn, I. Snigireva, B. Lengeler, A compound refractive lens for focusing high-energy X-rays. Nature **384**, 49–51 (1996). https://doi.org/10.1038/384049a0

214. S.R. Sutton, A. Lanzirrotti, M. Newville, M.L. Rivers, P. Eng, L. Lefticariu, Spatially resolved elemental analysis, spectroscopy and diffraction at the GSECARS sector at the advanced photon source. J. Environ. Qual. **46**, 1158–1165 (2017). https://doi.org/10.2134/jeq2016.10.0401

215. T.K. Sham, Y.Z. Finfrock, Q. Xiao, R. Feng, S. Bassnett, Retrieving images from tarnished daguerreotypes using X-ray fluorescence imaging with an X-ray micro beam with tunable energy. J. Cult. Herit. **67**, 53–61 (2024). https://doi.org/10.1016/j.culher.2024.02.003

216. B. Fayard, E. Pouyet, G. Berruyer, D. Bugnazet, C. Cornu, M. Cotte, V. De Andrade, F. Di Chiaro, O. Hignette, J. Kieffer, T. Martin, E. Papillon, M. Salomé, V.A. Sole, The new ID21 XANES full-field end-station at ESRF. J. Phys. Conf. Ser. **425**, 192001 (2013). https://doi.org/10.1088/1742-6596/425/19/192001

217. E. Pouyet, L. Monico, P. Sciau, M. Cotte, Application of Full-field X-ray Absorption Spectroscopy Imaging in Transmission Mode to Study Cultural Heritage Samples, in: Synchrotron Radiation, Cultural Heritage, Biomineralization, eds. By C. Dejoie, P. Martinetto, N. Tamura (Wiley-ISTE, 2024), pp. 69–100. https://doi.org/10.1002/9781394332458.ch3

218. E. Pouyet, B. Fayard, M. Salomé, Y. Taniguchi, F. Sette, M. Cotte, Thin-sections of painting fragments: opportunities for combined synchrotron-based micro-spectroscopic techniques. Herit. Sci. **3**, 3 (2015). https://doi.org/10.1186/s40494-014-0030-1

219. F. Pfeiffer, X-ray ptychography. Nat. Photonics **12**, 9–17 (2018). https://doi.org/10.1038/s41566-017-0072-5

220. P. Lechner, A. Pahlke, H. Soltau, Novel high-resolution silicon drift detectors. X-Ray Spectrom. **33**, 256–261 (2004). https://doi.org/10.1002/xrs.717

221. S.A. Audet, J.J. Friel, T.P. Gagliardi, R.B. Mott, J.I. Patel, C.G. Waldman, High resolution energy dispersive spectroscopy with high purity germanium detectors and digital pulse processing, in: IEEE Nuclear Science Symposium & Medical Imaging Conference (1995), pp. 155–159. https://doi.org/10.1109/nssmic.1994.474369

222. G. Falkenberg, F. Seiboth, F. Koch, K.V. Falch, A. Schropp, D. Brückner, J. Garrevoet, CRL optics and silicon drift detector for P06 Microprobe experiments at 35 keV. Powder Diffr. **35**(S1), S34–S37 (2020). https://doi.org/10.1017/S0885715620000536

223. C.G. Ryan, R. Kirkham, M.D. de Jonge, D.P. Siddons, A. van der Ent, A. Pagés, U. Boesenberg, A.J. Kuczewski, P. Dunn, M. Jensen, W. Liu, H. Harris, G.F. Moorhead, D.J. Paterson, D.L. Howard, N. Afshar, J. Garrevoet, K. Spiers, G. Falkenberg, A.R. Woll, G. De Geronimo, G.A. Carini, S.A. James, M.W.M. Jones, L.A. Fisher, M. Pearce, The Maia detector and event mode. Synchrotron Radiat. News **31**, 21–27 (2018). https://doi.org/10.1080/08940886.2018.1528430

224. U. Boesenberg, C.G. Ryan, R. Kirkham, D.P. Siddons, M. Alfeld, J. Garrevoet, T. Núñez, T. Claussen, T. Kracht, G. Falkenberg, Fast X-ray microfluorescence imaging with submicrometer-resolution integrating a Maia detector at beamline P06 at PETRA III. J. Synchrotron Radiat. **23**, 1550–1560 (2016). https://doi.org/10.1107/S1600577516015289
225. W. Chen, D. Elliott, G. Giacomini, A. Kuczewski, D. Pinelli, A.K. Rumaiz, D.P. Siddons, G. Smith, Improvement of SDD-Maia Detector for X-ray Fluorescence Detection, in: 2017 IEEE Nuclear Science Symposium and Medical Imaging Conference, NSS/MIC 2017 - Conference Proceedings (2018). https://doi.org/10.1109/NSSMIC.2017.8532602

226. O. Proux, E. Lahera, W. Del Net, I. Kieffer, M. Rovezzi, D. Testemale, M. Irar, S. Thomas, A. Aguilar-Tapia, E.F. Bazarkina, A. Prat, M. Tella, M. Auffan, J. Rose, J. Hazemann, High-energy resolution fluorescence detected X-ray absorption spectroscopy: a powerful new structural tool in environmental biogeochemistry sciences. J. Environ. Qual. 46, 1146-1157 (2017). https://doi.org/10.2134/jeq2017.01.0023

227. W.T. Elam, J.P. Kirkland, R.A. Neiser, P.D. Wolf, Depth dependence for extended X-ray-absorption fine-structure spectroscopy detected via electron yield in He and in vacuum. Phys. Rev. B 38, 26-30 (1988). https://doi.org/10.1103/PhysRevB.38.26

228. S. Padovani, I. Borgia, B. Brunetti, A. Sgamellotti, A. Giulivi, F. D'Acapito, P. Mazzoldi, C. Sada, G. Battaglin, Silver and copper nanoclusters in the lustre decoration of Italian Renaissance pottery: an EXAFS study. Appl. Phys. A Mater. Sci. Process. 79, 229-233 (2004). https://doi.org/10.1007/s00339-004-2516-2

229. G. Artioli, Science for the cultural heritage: the contribution of X-ray diffraction. Rend. Lincei. 24(Suppl 1), 55-62 (2013). https://doi.org/10.1007/s12210-012-0207-z

230. F. Vanmeert, K. De Wael, K. Janssens, G. Falkenberg, M. Cotte, Using synchrotron radiation for understanding the spontaneous degradation of artists' pigments. Synchrotron Radiat. News 32, 41-47 (2019). https://doi.org/10.1080/08940886.2019.1680214

231. V. Gonzalez, M. Cotte, F. Vanmeert, W. de Nolf, K. Janssens, X-ray diffraction mapping for cultural heritage science: a review of experimental configurations and applications. Chem. Eur. J. 26, 1703-1719 (2020). https://doi.org/10.1002/chem.201903284

232. C. Dejoie, P. Martinetto, N. Tamura, M. Kunz, F. Porcher, P. Bordat, R. Brown, E. Dooryhée, M. Anne, L.B. McCusker, Crystal structure of an indigo@silicalite hybrid related to the ancient maya blue pigment. J. Phys. Chem. C 118, 28032-28042 (2014). https://doi.org/10.1021/jp509969z

233. L. Monico, K. Janssens, C. Miliani, B.G. Brunetti, M. Vagnini, F. Vanmeert, G. Falkenberg, A. Abakumov, Y. Lu, H. Tian, J. Verbeeck, M. Radepont, M. Cotte, E. Hendriks, M. Geldof, L. Van Der Loeff, J. Salvant, M. Menu, Degradation process of lead chromate in paintings by Vincent van Gogh studied by means of spectromicroscopic methods. 3. Synthesis, characterization, and detection of different crystal forms of the chrome yellow pigment. Anal. Chem. 85, 851-859 (2013). https://doi.org/10.1021/ac302158b

234. F. Da Pieve, C. Hogan, D. Lamoen, J. Verbeeck, F. Vanmeert, M. Radepont, M. Cotte, K. Janssens, X. Gonze, G. Van Tendeloo, Casting light on the darkening of colors in historical paintings. Phys. Rev. Lett. 111, 208302 (2013). https://doi.org/10.1103/PhysRevLett.111.208302

235. L.M. Smieska, J. Twilley, A.R. Woll, M. Schafer, A. Marcereau DeGalan, Energy-optimized synchrotron XRF mapping of an obscured painting beneath Exit from the Theater, attributed to Honoré Daumier. Microchem. J. 146, 679-691 (2019). https://doi.org/10.1016/j.microc.2019.01.058

236. F. Vanmeert, W. De Nolf, J. Dik, K. Janssens, Macroscopic X-ray powder diffraction scanning: possibilities for quantitative and depth-selective parchment analysis. Anal. Chem. 90, 6445-6452 (2018). https://doi.org/10.1021/acs.analchem.8b00241

237. G. Chiari, P. Sarrazin, A. Heginbotham, Non-conventional applications of a noninvasive portable X-ray diffraction/fluorescence instrument. Appl. Phys. A Mater. Sci. Process. 122, 990 (2016). https://doi.org/10.1007/s00339-016-0521-x

238. P. Bleuet, E. Welcomme, E. Dooryhée, J. Susini, J.L. Hodeau, P. Walter, Probing the structure of heterogeneous diluted materials by diffraction tomography. Nat. Mater. 7, 468-472 (2008). https://doi.org/10.1038/nmat2168

239. W. De Nolf, K. Janssens, Micro X-ray diffraction and fluorescence tomography for the study of multilayered automotive paints. Surf. Interface Anal. 42, 411-418 (2010). https://doi.org/10.1002/sia.3125

240. E. Possenti, C. Conti, G.D. Gatta, N. Marinoni, M. Merlini, M. Realini, G.B.M. Vaughan, C. Colombo, Synchrotron X-ray diffraction computed tomography to non-destructively study inorganic treatments for stone conservation. IScience 25, 105112 (2022). https://doi.org/10.1016/j.isci.2022.105112

241. P. Bordet, F. Kergourlay, A. Pinto, N. Blanc, P. Martinetto, Applying multivariate analysis to X-ray diffraction computed tomography: the study of medieval applied brocades. J. Anal. At. Spectrom. 36, 1724-1734 (2021). https://doi.org/10.1039/d1ja00143d
242. M. Alfeld, K. Janssens, J. Dik, W. De Nolf, G. Van Der Snickt, Optimization of mobile scanning macro-XRF systems for the in situ investigation of historical paintings. J. Anal. At. Spectrom. 26, 899-909 (2011). https://doi.org/10.1039/c0ja00257g

243. M. Alfeld, J.V. Pedroso, M. Van Eikema Hommes, G. Van Der Snickt, G. Tauber, J. Blaas, M. Haschke, K. Erler, J. Dik, K. Janssens, A mobile instrument for in situ scanning macro-XRF investigation of historical paintings. J. Anal. At. Spectrom. 28, 760-767 (2013). https://doi.org/10.1039/c3ja30341a

244. M. Alfeld, W. De Nolf, S. Cagno, K. Appel, D.P. Siddons, A. Kuczewski, K. Janssens, J. Dik, K. Trentelman, M. Walton, A. Sartorius, Revealing hidden paint layers in oil paintings by means of scanning macro-XRF: A mock-up study based on Rembrandt's "An old man in military costume". J. Anal. At. Spectrom. 28, 40-51 (2013). https://doi.org/10.1039/c2ja30119a

245. J. Dik, K. Janssens, G. Van Der Snickt, L. Van Der Loeff, K. Rickers, M. Cotte, Visualization of a lost painting by Vincent van Gogh using synchrotron radiation based X-ray fluorescence elemental mapping. Anal. Chem. 80, 6436-6442 (2008). https://doi.org/10.1021/ac800965g

246. D. Thurrowgood, D. Paterson, M.D. De Jonge, R. Kirkham, S. Thurrowgood, D.L. Howard, A hidden portrait by Edgar Degas. Sci. Rep. 6, 29594 (2016). https://doi.org/10.1038/srep29594

247. L. Struick van der Loeff, M. Alfeld, T. Meedendorp, J. Dik, E. Hendriks, G. van der Snickt, J. Koen, C. Meta, Rehabilitation of a flower still life, in the Kröller-Müller Museum and a lost Antwerp painting by Van Gogh, in: Van Gogh: New Findings. Van Gogh Studies, 4th edn., ed. by L. van Tilborgh (Waanders BV, Zwolle, 2012), pp. 33-53

248. M. Alfeld, K. Janssens, K. Appel, B. Thijsse, J. Blaas, J. Dik, A portrait by Philipp Otto Runge: visualizing modifications to the painting using synchrotron-based X-ray fluorescence elemental scanning. Zeitschrift Für Kunssttechnologie Und Konservierung 25, 157-163 (2011)

249. D.L. Howard, M.D. De Jonge, D. Lau, D. Hay, M. Varcoe-Cocks, C.G. Ryan, R. Kirkham, G. Moorhead, D. Paterson, D. Thurrowgood, High-definition X-ray fluorescence elemental mapping of paintings. Anal. Chem. 84, 3278-3286 (2012). https://doi.org/10.1021/ac203462h

250. M. Alfeld, D.P. Siddons, K. Janssens, J. Dik, A. Woll, R. Kirkham, E. Van De Wetering, Visualizing the 17th century underpainting in Portrait of an Old Man by Rembrandt van Rijn using synchrotron-based scanning macro-XRF. Appl. Phys. A Mater. Sci. Process. 111, 157-164 (2013). https://doi.org/10.1007/s00339-012-7490-5

251. M. Alfeld, K. Janssens, Strategies for processing mega-pixel X-ray fluorescence hyperspectral data: a case study on a version of Caravaggio's painting Supper at Emmaus. J. Anal. At. Spectrom. 30, 777-789 (2015). https://doi.org/10.1039/c4ja00387j

252. K. Janssens, J. Dik, M. Cotte, J. Susini, Photon-based techniques for nondestructive subsurface analysis of painted cultural heritage artifacts. Acc. Chem. Res. 43, 814-825 (2010). https://doi.org/10.1021/ar900248e

253. K. Stonor, C. Richardson, S.R. Amato, A. Nevin, A. Burnstock, Rubens's Death of Hippolytus (1610-12): How scanning XRF shed new light on old questions, in: Lasers in the Conservation of Artworks XIII - Proceedings of the International Conference on Lasers in the Conservation of Artworks XII, LACONA 2022 (2024), pp. 3-11. https://doi.org/10.1201/9781003386872-1

254. K. Trentelman, K. Janssens, G. van der Snickt, Y. Szafran, A.T. Woollett, J. Dik, Rembrandt's An Old Man in Military Costume: the underlying image re-examined. Appl. Phys. A Mater. Sci. Process. 121, 801-811 (2015). https://doi.org/10.1007/s00339-015-9426-3

255. K. Janssens, G. Van Der Snickt, M. Alfeld, P. Noble, A. van Loon, J. Delaney, D. Conover, J. Zeibel, J. Dik, Rembrandt's "Saul and David" (c. 1652): use of multiple types of smalt evidenced by means of non-destructive imaging. Microchem. J. 126, 515-523 (2016). https://doi.org/10.1016/j.microc.2016.01.013

256. P. Noble, A. van Loon, M. Alfeld, K. Janssens, J. Dik, Rembrandt and/or studio, Saul and David, c. 1655: visualising the curtain using cross-section analyses and X-ray fluorescence imaging. Techne 35, 36-45 (2012)

257. I. Verslype, The restoration of woman in blue reading a letter by Johannes Vermeer. Rijksmuseum Bull. 60, 3-18 (2012). https://doi.org/10.52476/trb.9694

258. D. Bull, A. Krekeler, M. Alfeld, J. Dik, K. Janssens, An intrusive portrait by Goya. Burlington Magazine 153, 668-672 (2011)

259. S.R. Amato, A. Burnstock, Scanning X-ray fluorescence for the re-examination of the composition underneath Paul Gauguin's Nevermore in the Courtauld Gallery. Stud. Conserv. (2024). https://doi.org/10.1080/00393630.2024.2350276
260. K.A. Dooley, A. Chieli, A. Romani, S. Legrand, C. Miliani, K. Janssens, J.K. Delaney, Molecular fluorescence imaging spectroscopy for mapping low concentrations of red lake pigments: Van Gogh's painting The olive orchard. Angewandte Chemie - Int. Ed. **59**, 6046-6053 (2020). https://doi.org/10.1002/anie.201915490

261. G. Van Der Snickt, A. Martins, J. Delaney, K. Janssens, J. Zeibel, M. Duffy, C. McGlinchey, B. Van Driel, J. Dik, Exploring a hidden painting below the surface of René Magritte's Le portrait. Appl. Spectrosc. **70**, 57-67 (2016). https://doi.org/10.1177/0003702815617123

262. A.T. da Silva, S. Legrand, G. van der Snickt, R. Featherstone, K. Janssens, G. Bottinelli, MA-XRF imaging on René Magritte's La condition humaine: Insights into the artist's palette and technique and the discovery of a third quarter of La pose enchantée. Herit. Sci. **5**, 37 (2017). https://doi.org/10.1186/s40494-017-0150-5

263. E. Derzelle, D. Strivay, A. Defeyt, S.J. Klein, F. Vandepitte, C. Defeyt, Paul Delvaux: the study of nine paintings by non-invasive methods. Heritage **6**, 7181-7201 (2023). https://doi.org/10.3390/heritage6110376

264. A. Martins, C. Albertson, C. McGlinchey, J. Dik, Piet Mondrian's Broadway Boogie Woogie: non invasive analysis using macro X-ray fluorescence mapping (MA-XRF) and multivariate curve resolution-alternating least square (MCR-ALS). Herit. Sci. **4**, 22 (2016). https://doi.org/10.1186/s40494-016-0091-4

265. A. Martins, J. Coddington, G. Snickt, B. Driel, C. McGlinchey, D. Dahlberg, K. Janssens, J. Dik, Jackson Pollock's Number 1A, 1948: A non-invasive study using macro-X-ray fluorescence mapping (MA-XRF) and multivariate curve resolution-alternating least squares (MCR-ALS) analysis. Herit Sci **4**, 33 (2016). https://doi.org/10.1186/s40494-016-0105-2

266. M. Cotte, L. Monico, K. Janssens, W. De Nolf, M. Salomé, J. Langlois, Synchrotron-based micro-analyses of artistic materials at ID21, ESRF. Acta Crystallogr. A Found. Adv. **73**, C1344-C1344 (2017). https://doi.org/10.1107/s2053273317082316

267. S. Legrand, P. Ricciardi, L. Nodari, K. Janssens, Non-invasive analysis of a 15th century illuminated manuscript fragment: point-based vs imaging spectroscopy. Microchem. J. **138**, 162-172 (2018). https://doi.org/10.1016/j.microc.2018.01.001

268. P. Ricciardi, S. Legrand, G. Bertolotti, K. Janssens, Macro X-ray fluorescence (MA-XRF) scanning of illuminated manuscript fragments: potentialities and challenges. Microchem. J. **124**, 785-791 (2016). https://doi.org/10.1016/j.microc.2015.10.020

269. M. Perino, L. Pronti, C. Moffa, M. Rosellini, A.C. Felici, New frontiers in the digital restoration of hidden texts in manuscripts: a review of the technical approaches. Heritage **7**, 683-696 (2024). https://doi.org/10.3390/heritage7020034

270. G. Bartolozzi, A. Casini, L. Castelli, C. Cucci, F. Grazzi, A. Mazzinghi, I. Pieralli, C. Ruberto, R. Sarfati, A. Sidoti, L. Stefani, M. Picollo, The non-invasive spectroscopic study of a parchment object from the national central library of florence: the hebrew scroll. Heritage **7**, 206-224 (2024). https://doi.org/10.3390/heritage7010011

271. F. Fiorillo, E. Cheese, S. Öberg Strádal, S. Reynolds, The extraordinary universe of Peter Apian: technical investigation of five copies of a 16th-century astronomical book. Herit. Sci. **12**, 190 (2024). https://doi.org/10.1186/s40494-024-01306-1

272. A. Piccirillo, P. Buscaglia, C. Caliri, F.P. Romano, D.P. Pavone, E.L. Ravan, M. Botticelli, C. Conti, C.M. Maria Catrambone, I. Degano, F.N. Alessia Andreotti, M. Samadelli, A. Paladin, R. Genta, M. Cardinali, F. Pozzi, D. Picchi, Unraveling the mummy's shroud: a multi-analytical study of a rare painted textile from Roman Egypt. J. Cult. Herit. **68**, 107-121 (2024). https://doi.org/10.1016/j.culher.2024.05.006

273. S. Cagno, G. Van der Snickt, S. Legrand, J. Caen, M. Patin, W. Meulebroeck, Y. Dirkx, M. Hillen, G. Steenackers, A. Rousaki, P. Vandenabeele, K. Janssens, Comparison of four mobile, non-invasive diagnostic techniques for differentiating glass types in historical leaded windows: MA-XRF, UV-Vis-NIR, Raman spectroscopy and IRT. X-Ray Spectrom. **50**, 293-309 (2021). https://doi.org/10.1002/xrs.3185

274. S. Legrand, G. Van der Snickt, S. Cagno, J. Caen, K. Janssens, MA-XRF imaging as a tool to characterize the 16th century heraldic stained-glass panels in Ghent Saint Bavo Cathedral. J. Cult. Herit. **40**, 163-168 (2019). https://doi.org/10.1016/j.culher.2019.06.003

275. M. Vadrucci, M. Chiari, A. Mazzinghi, A. Rufoloni, C. Cicero, "Hearts of gold" (Cuori d'oro): the case study of the leather corami of Palazzo Chigi in Ariccia. J. Cult. Herit. **68**, 184-194 (2024). https://doi.org/10.1016/j.culher.2024.05.017
276. I. Vanden Berghe, M. Van Bos, M. Vandorpe, A. Coudray, Non-invasive analysis of heritage textiles with MA-XRF mapping—exploring the possibilities. The study of Bishop Jacques de Vitry’s mitres and fragile medieval reliquary purses from Namur (Belgium). Herit Sci **11**, 183 (2023). https://doi.org/10.1186/s40494-023-00977-6

277. W. Liu, P.Y. Zhang, N. Wu, The spectroscopic analysis of corrosion products on gold-painted copper-based bodhisattva (Guanyin) in half lotus position from national museum of China. Guang Pu Xue Yu Guang Pu Fen Xi/Spectroscopy and Spectral Analysis **43**, 3832–3839 (2023). https://doi.org/10.3964/j.issn.1000-0593(2023)12-3832-08

278. J. Brocchieri, R. Vitale, C. Sabbarese, MA-XRF analysis of ancient silver coins minted in southern Italy. X-Ray Spectrom. **53**, 452–463 (2023). https://doi.org/10.1002/xrs.3395

279. K.A. Dooley, D.M. Conover, L.D. Glinsman, J.K. Delaney, Complementary standoff chemical imaging to map and identify artist materials in an early Italian renaissance panel painting. Angewandte Chemie – Int. Ed. **53**, 13775–13779 (2014). https://doi.org/10.1002/anie.201407893

280. E. Ravaud, L. Pichon, E. Laval, V. Gonzalez, M. Eveno, T. Calligaro, Development of a versatile XRF scanner for the elemental imaging of paintworks. Appl. Phys. A Mater. Sci. Process. **122**, 17 (2016). https://doi.org/10.1007/s00339-015-9522-4

281. F.P. Romano, C. Caliri, P. Nicotra, S. Di Martino, L. Pappalardo, F. Rizzo, H.C. Santos, Real-time elemental imaging of large dimension paintings with a novel mobile macro X-ray fluorescence (MA-XRF) scanning technique. J. Anal. At. Spectrom. **32**, 773–781 (2017). https://doi.org/10.1039/c6ja00439c

282. R. Alberti, T. Frizzi, L. Bombelli, M. Gironda, N. Aresi, F. Rosi, C. Miliani, G. Tranquilli, F. Talarico, L. Cartechini, CRONO: a fast and reconfigurable macro X-ray fluorescence scanner for in-situ investigations of polychrome surfaces. X-Ray Spectrom. **46**, 297–302 (2017). https://doi.org/10.1002/xrs.2741

283. F.P. Romano, K. Janssens, Preface to the special issue on: MA-XRF “developments and applications of macro-XRF in conservation, art, and archeology” (Trieste, Italy, 24 and 25 September 2017). X-Ray Spectrom. **48**, 249–250 (2019). https://doi.org/10.1002/xrs.3047

284. F.P. Romano, ed., Special Issue: MA-XRF. X-Ray Spectrometry **50**, 243–412 (2021)

285. J.K. Delaney, K.A. Dooley, K. Janssens, A collection of papers from the 2024 Macro X-ray Fluorescence and Reflectance Imaging Spectroscopy Meeting. https://www.springeropen.com/collections/MAXRF. Accessed June 2025

286. M. Alfeld, J.A.C. Broekaert, Mobile depth profiling and sub-surface imaging techniques for historical paintings—a review. Spectrochim. Acta Part B At. Spectrosc. **88**, 211–230 (2013). https://doi.org/10.1016/j.sab.2013.07.009

287. L. Musflek, T. Čechák, T. Trojek, X-ray fluorescence analysis in the study of paintings – an overview. Radiat. Eff. Defects Solids **179**, 1218–1232 (2024). https://doi.org/10.1080/10420150.2024.2332215

288. A. Harth, X-ray fluorescence (XRF) on painted heritage objects: a review using topic modeling. Herit. Sci. **12**, 17 (2024). https://doi.org/10.1186/s40494-024-01135-2

289. A. Gestels, F. Gabrieli, T. De Kerf, F. Vanmeert, H. García, J. Delaney, K. Janssens, G. Steenackers, S. Vanlanduit, High-resolution compound-specific mapping in works of art via data fusion of MA-XRPD with hyperspectral data (part 1: Method evaluation). Talanta **280**, 126731 (2024). https://doi.org/10.1016/j.talanta.2024.126731

290. S. Yan, J.J. Huang, H. Verinaz-Jadan, N. Daly, C. Higgitt, P.L. Dragotti, A fast automatic method for deconvoluting macro X-ray fluorescence data collected from easel paintings. IEEE Trans. Comput. Imaging **9**, 649–664 (2023). https://doi.org/10.1109/TCI.2023.3288343

291. G. Pastorelli, A.S. Ortiz Miranda, A.H. Christensen, Interpretation of X-ray spectral data using self-organising maps and hierarchical clustering: a study of Vilhelm Hammershøi's use of painting materials. X-Ray Spectrom. **53**, 392–404 (2024). https://doi.org/10.1002/xrs.3388

292. T. Gerodimos, I. Patakiouta, V. Papadakis, D. Exarchos, A. Asvestas, G. Kenanakis, D. Matikas, T. Anagnostopoulos, Scanning micro X-ray fluorescence and multispectral imaging fusion: a case study on postage stamps. J Imaging **10**, 95 (2024). https://doi.org/10.3390/jimaging10040095

293. M. Vermeulen, A. McGeachy, B. Xu, H. Chopp, A. Katsaggelos, R. Meyers, M. Alfeld, M. Walton, XRFast a new software package for processing of MA-XRF datasets using machine learning. J. Anal. At. Spectrom. **37**, 2130–2143 (2022). https://doi.org/10.1039/d2ja00114d

294. E. Pouyet, S. Devine, T. Grafakos, R. Kieckhefer, J. Salvant, L. Smieska, A. Woll, A. Katsaggelos, O. Cossairt, M. Walton, Revealing the biography of a hidden medieval manuscript using synchrotron
and conventional imaging techniques. *Anal. Chim. Acta* **982**, 20–30 (2017). https://doi.org/10.1016/j.aca.2017.06.016

295. Z. Preisler, R. Andolina, A. Busacca, C. Caliri, C. Miliani, F.P. Romano, Deep learning for enhanced spectral analysis of MA-XRF datasets of paintings. *Sci. Adv.* **10**, eadp6234 (2024). https://doi.org/10.1126/sciadv.adp6234

296. T. Trojek, R. Prokeš, R. Šefčů, H. Bilavčíková, T. Čechák, Confocal X-ray fluorescence spectrometer for in-situ analyses of paintings. *Radiat. Phys. Chem.* **137**, 238–242 (2017). https://doi.org/10.1016/j.radphyschem.2016.02.031

297. C. Seim, C. Laurenze-Landsberg, B. Schröder-Smeibidl, I. Mantouvalou, C. De Boer, B. Kanngießer, Old traces, read anew-, 'The Reading Hermit' painting in the light of X-ray fluorescence. *J. Anal. At. Spectrom.* **29**, 1354–1360 (2014). https://doi.org/10.1039/c3ja50301a

298. T. Lachmann, G. Van Der Snickt, M. Haschke, I. Mantouvalou, Combined 1D, 2D and 3D micro-XRF techniques for the analysis of illuminated manuscripts. *J. Anal. At. Spectrom.* **31**, 1989–1997 (2016). https://doi.org/10.1039/c6ja00220j

299. J. Tapia, M. Eveno, E. Laval, I. Reiche, Depth-resolved historical painting study with minimal microsampling, illustrated with a newly discovered Botticelli workshop painting. *X-Ray Spectrom.* (2024). https://doi.org/10.1002/xrs.3430

300. V.A. Solé, E. Papillon, M. Cotte, P. Walter, J. Susini, A multiplatform code for the analysis of energy-dispersive X-ray fluorescence spectra. *Spectrochim. Acta Part B At. Spectrosc.* **62**, 63–68 (2007). https://doi.org/10.1016/j.sab.2006.12.002

301. M. Cotte, T. Fabris, G. Agostini, D. Motta Meira, L. De Viguerie, V.A. Solé, Watching kinetic studies as chemical maps using open-source software. *Anal. Chem.* **88**, 6154–6160 (2016). https://doi.org/10.1021/acs.analchem.5b04819

302. S.M. Webb, The microAnalysis toolkit: X-ray fluorescence image processing software. *AIP Conf. Proc.* **1365**, 196–199 (2010). https://doi.org/10.1063/1.3625338

303. A.P. Hitchcock, Analysis of X-ray images and spectra (aXis2000): A toolkit for the analysis of X-ray spectromicroscopy data. *J. Electron. Spectros. Relat. Phenomena* **266**, 147360 (2023). https://doi.org/10.1016/j.elspec.2023.147360

304. Y. Liu, F. Meirer, P.A. Williams, J. Wang, J.C. Andrews, P. Pianetta, TXM-Wizard: A program for advanced data collection and evaluation in full-field transmission X-ray microscopy. *J. Synchrotron Radiat.* **19**, 281–287 (2012). https://doi.org/10.1107/S0909049511049144

305. B. Ravel, M. Newville, ATHENA, ARTEMIS, HEPHAESTUS: Data analysis for X-ray absorption spectroscopy using IFEFFIT. *J. Synchrotron Radiat.* **12**, 537–541 (2005). https://doi.org/10.1107/S0909049505012719

306. S.M. Webb, SIXpack: A graphical user interface for XAS analysis using IFEFFIT. *Phys. Scr. T.* **T115**, 1011–1014 (2005). https://doi.org/10.1238/Physica.Topical.115a01011

307. J.J. Rehr, J.J. Kas, F.D. Vila, M.P. Prange, K. Jorissen, Parameter-free calculations of X-ray spectra with FEFF9. *Phys. Chem. Chem. Phys.* **12**, 5503–5513 (2010). https://doi.org/10.1039/b926434e

308. S. Tomic, B.G. Searle, A. Wander, N.M. Harrison, A.J. Dent, J.F.W. Mosselmans, J.E. Inglesfield, New tools for the analysis of EXAFS: the DL EXCURV package. *Council for the Central Laboratory of the Research Councils* (2005)

309. A. Filipponi, A. Di Cicco, X-ray-absorption spectroscopy and n-body distribution functions in condensed matter. II. Data analysis and applications. *Phys. Rev. B* **52**, 15135–15149 (1995). https://doi.org/10.1103/PhysRevB.52.15135

310. M. Ippoliti, F. Guzzi, A. Gianoncelli, F. Billè, G. Kourousias, XRFitProc: a novel web-based X-ray fluorescence fitting system. *X-Ray Spectrom.* **52**, 371–377 (2023). https://doi.org/10.1002/xrs.3341

311. L.L. Van Loon, N.S. McIntyre, M. Bauer, N.S.A. Sherry, N.R. Banerjee, Peakaboo: Advanced software for the interpretation of X-ray fluorescence spectra from synchrotrons and other intense X-ray sources. *Software Impacts* **2**, 100010 (2019). https://doi.org/10.1016/j.simpa.2019.100010

312. H. Yan, W. Xu, D. Yu, A. Heroux, W.-K. Lee, L. Li, S. Campbell, Y. Chu, PyXRF: Python-based X-ray fluorescence analysis package, in: X-Ray Nanoimaging: Instruments and Methods III. SPIE (2017), pp. 38–45. https://doi.org/10.1117/12.2272585

313. S. Vogt, MAPS: A set of software tools for analysis and visualization of 3D X-ray fluorescence data sets. *J. Phys. IV France* **104**, 635–638 (2003). https://doi.org/10.1051/jp4:20030160

314. C.G. Ryan, B.E. Etschmann, S. Vogt, J. Maser, C.L. Harland, E. Van Achterbergh, D. Legnini, Nuclear microprobe-synchrotron synergy: Towards integrated quantitative real-time elemental imaging using
PIXE and SXRF. Nucl Instrum Methods Phys Res B **231**, 183-188 (2005). https://doi.org/10.1016/j.nimb.2005.01.054

315. C.G. Ryan, J.S. Laird, L.A. Fisher, R. Kirkham, G.F. Moorhead, Improved dynamic analysis method for quantitative PIXE and SXRF element imaging of complex materials. Nucl. Instrum. Methods Phys. Res. B **363**, 42-47 (2015). https://doi.org/10.1016/j.nimb.2015.08.021

316. O. Bunău, Y. Joly, Self-consistent aspects of X-ray absorption calculations. J. Phys. Condens. Matter **21**, 345501 (2009). https://doi.org/10.1088/0953-8984/21/34/345501

317. C.T. Chantler, F. Boscherini, B. Bunker, X-ray absorption spectroscopy and related techniques. Int. Tables Crystallogr. (2020). https://doi.org/10.1107/97809553602060000116

318. J. Kieffer, V. Valls, N. Blanc, C. Hennig, New tools for calibrating diffraction setups. J. Synchrotron Radiat. **27**, 558-566 (2020). https://doi.org/10.1107/S1600577520000776

319. S. Gates-Rector, T. Blanton, The Powder Diffraction File: a quality materials characterization database. Powder Diffr. **34**, 352-360 (2019). https://doi.org/10.1017/S0885715619000812

320. D. Zagorac, H. Muller, S. Ruehl, J. Zagorac, S. Rehme, Recent developments in the Inorganic Crystal Structure Database: Theoretical crystal structure data and related features. J. Appl. Crystallogr. **52**, 918-925 (2019). https://doi.org/10.1107/S160057671900997X

321. C.R. Groom, I.J. Bruno, M.P. Lightfoot, S.C. Ward, The Cambridge structural database. Acta Crystallogr B Struct. Sci. Cryst. Eng. Mater. **72**, 171-179 (2016). https://doi.org/10.1107/S2052520616003954

322. R.T. Downs, M. Hall-Wallace, The American Mineralogist crystal structure database. Am. Miner. **88**, 247-250 (2003). https://doi.org/10.5860/choice.43sup-0302

323. S. Gražulis, A. Merkys, A. Vaitkus, Crystallography Open Database (COD), in: Handbook of Materials Modeling, eds. By W. Andreoni, S. Yip (Springer, Cham, 2020), pp. 1863-1881. https://doi.org/10.1007/978-3-319-44677-6_66

324. H. Putz, K. Brandenburg GbR, Match! Phase Analysis using Powder Diffraction, Crystal Impact. (n.d.). https://www.crystalimpact.de/match (Accessed November 2024)

325. A. Altomare, N. Corriero, C. Cuocchi, A. Falcicchio, A. Moliterni, R. Rizzi, QUALX2.0: a qualitative phase analysis software using the freely available database POW_COD. J. Appl. Crystallogr. **48**, 598-603 (2015). https://doi.org/10.1107/S1600576715002319

326. B.H. Toby, R.B. Von Dreele, GSAS-II: the genesis of a modern open-source all purpose crystallography software package. J. Appl. Crystallogr. **46**, 544-549 (2013). https://doi.org/10.1107/S0021889813003531

327. H.M. Rietveld, A profile refinement method for nuclear and magnetic structures. J. Appl. Crystallogr. **2**, 65-71 (1969). https://doi.org/10.1107/s0021889869006558

328. C.J. Gilmore, J.A. Kaduk, H. Schenk, Powder diffraction. Int. Tables Crystallogr. (2019). https://doi.org/10.1107/97809553602060000115

329. B.M. Weckhuysen, Z. Öztürk, R.P. Brand, J.M. Boereboom, F. Meirer, Vibrational fingerprinting of defects sites in thin films of zeolitic imidazolate frameworks. Chem. Eur. J. **25**, 8070-8084 (2019). https://doi.org/10.1002/chem.201806414

330. I.K. Van Ravenhorst, A.S. Hoffman, C. Vogt, A. Boubnov, N. Patra, R. Oord, C. Akatay, F. Meirer, S.R. Bare, B.M. Weckhuysen, On the cobalt carbide formation in a Co/TiO₂ fischer-tropsch synthesis catalyst as studied by high-pressure, long-term operando X-ray absorption and diffraction. ACS Catal. **11**, 2956-2967 (2021). https://doi.org/10.1021/acscatal.0c04695

331. F. Meirer, Y. Liu, E. Pouyet, B. Fayard, M. Cotte, C. Sanchez, J.C. Andrews, A. Mehta, P. Sciau, Full-field XANES analysis of Roman ceramics to estimate firing conditions - A novel probe to study hierarchical heterogeneous materials. J. Anal. At. Spectrom. **28**, 1870-1883 (2013). https://doi.org/10.1039/c3ja50226k

332. L. Monico, L. Cartechini, F. Rosi, W. De Nolf, M. Cotte, R. Vivani, C. Maurich, C. Miliani, Synchrotron radiation Ca K-edge 2D-XANES spectroscopy for studying the stratigraphic distribution of calcium-based consolidants applied in limestones. Sci. Rep. **10**, 14337 (2020). https://doi.org/10.1038/s41598-020-71105-8

333. P. Ballirano, M. Botticelli, A. Maras, Thermal behaviour of cinnabar, α-HgS, and the kinetics of the β-HgS (metacinnabar) - α-HgS conversion at room temperature. Eur. J. Mineral. **25**, 957-965 (2014). https://doi.org/10.1127/0935-1221/2013/0025-2341

334. A. Kyono, M. Kimata, T. Hatta, Light-induced degradation dynamics in realgar: In situ structural investigation using single-crystal X-ray diffraction study and X-ray photoelectron spectroscopy. Am. Miner. **90**, 1563-1570 (2005). https://doi.org/10.2138/am.2005.1785
335. P. Ballirano, A. Maras, In-situ X-ray transmission powder diffraction study of the kinetics of the light induced alteration of realgar (α-As₄S₄). Eur. J. Mineral. **18**, 589–599 (2006). https://doi.org/10.1127/0935-1221/2006/0018-0589

336. W. De Nolf, H. Payno, O. Svensson, G. Koumoutsos, ewoks (0.5.0). Zenodo (2024). https://doi.org/10.5281/zenodo.12704398

337. J. Demšar, T. Kurc, A. Erjavec, Č Gorup, T. Hočevar, M. Milutinovič, M. Možina, M. Polajnar, M. Toplak, A. Starič, M. Štajdohar, L. Umek, L. Žagar, J. Žbontar, M. Žitnik, B. Zupan, Orange: Data mining toolbox in python. J. Mach. Learn. Res. **14**, 2349–2353 (2013)

338. A. Gotz, J. F. Perrin, H. Fangohr, D. Salvat, F. Gliksohn, A. Markvardsen, A. McBirnie, A. Gonzalez-Beltran, J. Taylor, B. Matthews. PaNOSC FAIR Research Data Policy framework (1.1). Zenodo (2020). https://doi.org/10.5281/zenodo.3862701

339. T. Wang, T.Q. Zhu, Z.Y. Feng, B. Fayard, E. Pouyet, M. Cotte, W. De Nolf, M. Salomé, P. Sciau, Synchrotron radiation-based multi-analytical approach for studying underglaze color: the microstructure of Chinese Qinghua blue decors (Ming dynasty). Anal. Chim. Acta **928**, 20–31 (2016). https://doi.org/10.1016/j.aca.2016.04.053

340. P. Sciau, C. Sanchez, E. Gliozzo, Ceramic technology: how to characterize terra sigillata ware. Archaeol. Anthropol. Sci. **12**, 211 (2020). https://doi.org/10.1007/s12520-020-01137-8

341. G. Massinelli, N. Marinoni, C. Colombo, G.D. Gatta, M. Realini, M. Burghammer, E. Possenti, Advanced mapping of inorganic treatments on porous carbonate stones by combined synchrotron radiation high lateral µ-XRPD and µ-XRF. Sci. Rep. **14**, 9108 (2024). https://doi.org/10.1038/s41598-024-58718-z

342. E. Pouyet, A. Lluveras-Tenorio, A. Nevin, D. Saviello, F. Sette, M. Cotte, Preparation of thin-sections of painting fragments: classical and innovative strategies. Anal. Chim. Acta **822**, 51–59 (2014). https://doi.org/10.1016/j.aca.2014.03.025

343. A. Gianoncelli, L. Vaccari, G. Kourousias, D. Cassese, D.E. Bedolla, S. Kenig, P. Storici, M. Lazzarino, M. Kiskinova, Soft X-ray microscopy radiation damage on fixed cells investigated with synchrotron. Sci. Reports **5**, 10250 (2015). https://doi.org/10.1038/srep10250

344. E.F. Garmana, M. Weik, Radiation damage to biological samples: still a pertinent issue. Synchrotron Radiat. **28**, 1278–1283 (2021). https://doi.org/10.1107/S1600577521008845

345. R.A. Wogelius, P.L. Manning, H.E. Barden, N.P. Edwards, S.M. Webb, W.I. Sellers, K.G. Taylor, P.L. Larson, P. Dodson, H. You, L. Da-qing, U. Bergmann, Trace metals as biomarkers for eumelanin pigment in the fossil record. Science **1979**(333), 1622–1626 (2011). https://doi.org/10.1126/science.1205748

346. S.R. Stock, M.K. Stock, J.D. Almer, Combined computed tomography and position-resolved X-ray diffraction of an intact Roman-era Egyptian portrait mummy: Combined computed tomography and position-resolved X-ray diffraction of an intact Roman-era Egyptian portrait mummy. J. R. Soc. Interface. **17**, 20200686 (2020). https://doi.org/10.1098/rsif.2020.0686

347. C. Gervais, M.A. Lanquille, G. Moretti, S. Réguer, Time resolved XANES illustrates a substrate-mediated redox process in Prussian blue cultural heritage materials. J. Phys. Conf. Ser. **712**, 012139 (2016). https://doi.org/10.1088/1742-6596/712/1/012139

348. Z. Zhang, Z. Liu, Y. Jiang, H. Zhu, T. Ji, J. Wang, M. Chen, W. Peng, L. Wang, X. Wei, In situ investigation of synchrotron radiation damage effect of ancient paintings by time-resolved ED-XAS and IR combined techniques. X-Ray Spectrom. **51**, 394–402 (2022). https://doi.org/10.1002/xrs.3289

349. Y. Li, A. Suzuki, C.S. Cheung, Y. Gu, S. Kogou, H. Liang, A study of potential laser-induced degradation in remote standoff Raman spectroscopy for wall paintings. Eur. Phys. J. Plus **137**, 1102 (2022). https://doi.org/10.1140/epjp/s13360-022-03305-2

350. L. Burgio, R.J.H. Clark, S. Firth, Raman spectroscopy as a means for the identification of plattnerite (PbO₂), of lead pigments and of their degradation products. Analyst **126**, 222–227 (2001). https://doi.org/10.1039/b008302j

351. I. Osticioli, A.A. Mencaglia, S. Siano, Temperature-controlled portable Raman spectroscopy of photothermally sensitive pigments. Sens Actuators B Chem. **238**, 772–778 (2017). https://doi.org/10.1016/j.snb.2016.07.104

352. A. Philippidis, A. Mikallou, D. Anglos, Determining optimum irradiation conditions for the analysis of vermilion by Raman spectroscopy. Eur. Phys. J. Plus **136**, 1194 (2021). https://doi.org/10.1140/epjp/s13360-021-02186-1

353. G. Moretti, C. Gervais, Raman spectroscopy of the photosensitive pigment Prussian blue. J. Raman Spectrosc. **49**, 1198–1204 (2018). https://doi.org/10.1002/jrs.5366
354. L. Monico, K. Janssens, E. Hendriks, B.G. Brunetti, C. Miliani, Raman study of different crystalline forms of PbCrO₄ and PbCr₁-xSxO₄ solid solutions for the noninvasive identification of Chrome yellows in paintings: A focus on works by Vincent van Gogh. J. Raman Spectrosc. **45**, 1034–1045 (2014). https://doi.org/10.1002/jrs.4548

355. R. Clarke, J. Valentin, A history of the international commission on radiological protection. Health Phys. **88**, 407–422 (2005). https://doi.org/10.1097/01.HP.0000154049.41251.1e

356. IAEA - Internation Atomic Energy Agency, IAEA Annual Report 2017 (2018). https://www.iaea.org/opic/annual-report-2017. Accessed June 2025

357. I. Joosten, M. Stols-Witlox, Maartje Tromp, K. Keune, Irradiation Passport for Art (IPA), in: IAEA Workshop on Innovative Approaches of Accelerator Science and Technology for Sustainable Heritage Management (IAEA, Vienna, 2022), pp. 39–40. https://conferences.iaea.org/event/291/

358. L. Robinet, M.C. Corbeil, The characterization of metal soaps. Stud. Conserv. **48**, 23–40 (2003). https://doi.org/10.1179/sic.2003.48.1.23

359. V. Otero, D. Sanches, C. Montagner, M. Vilarigues, L. Carlyle, J.A. Lopes, M.J. Melo, Characterisation of metal carboxylates by Raman and infrared spectroscopy in works of art. J. Raman Spectrosc. **45**, 1197–1206 (2014). https://doi.org/10.1002/jrs.4520

360. F. Rosi, L. Cartechini, L. Monico, F. Gabrieli, M. Vagnini, D. Buti, B. Doherty, C. Anselmi, B.G. Brunetti, C. Miliani, Tracking Metal Oxalates and Carboxylates on Painting Surfaces by Non-invasive Reflection Mid-FTIR Spectroscopy, in: Metal Soaps in Art: Conservation and Research, eds. By F. Casadio, K. Keune, P. Noble, A. Van Loon, E. Hendriks, S.A. Centeno, G. Osmond (Springer International Publishing, Switzerland, 2019), pp. 173–193. https://doi.org/10.1007/978-3-319-90617-1_10

361. J. Catalano, V. Di Tullio, M. Wagner, N. Zumbulyadis, S.A. Centeno, C. Dybowski, Review of the use of NMR spectroscopy to investigate structure, reactivity, and dynamics of lead soap formation in paintings. Magn. Reson. Chem. **58**, 798–811 (2020). https://doi.org/10.1002/mrc.5025

362. K. Keune, A. Van Loon, J.J. Boon, SEM backscattered-electron images of paint cross-sections as information source for the presence of the lead white pigment and lead-related degradation and migration phenomena in oil paintings. Microsc. Microanal. **17**, 696–701 (2011). https://doi.org/10.1017/S1431927610094444

363. M. Cotte, E. Checroun, J. Susini, P. Walter, Micro-analytical study of interactions between oil and lead compounds in paintings. Appl. Phys. A Mater. Sci. Process. **89**, 841–848 (2007). https://doi.org/10.1007/s00339-007-4213-4

364. Y.C.K. Chen-Wiegart, J. Catalano, G.J. Williams, A. Murphy, Y. Yao, N. Zumbulyadis, S.A. Centeno, C. Dybowski, J. Thieme, Elemental and molecular segregation in oil paintings due to lead soap degradation. Sci. Rep. **7**, 11656 (2017). https://doi.org/10.1038/s41598-017-11525-1

365. M.C. Corbeil, L. Robinet, X-ray powder diffraction data for selected metal soaps. Powder Diffr. **17**, 52–60 (2002). https://doi.org/10.1154/1.1431950

366. E. Kočí, J. Rohlíček, L. Kobera, J. Plocek, S. Švarcová, P. Bezdička, Mixed lead carboxylates relevant to soap formation in oil and tempera paintings: The study of the crystal structure by complementary XRPD and ssNMR. Dalton Trans. **48**, 12531–12540 (2019). https://doi.org/10.1039/c9dt02040c

367. M. Cotte, E. Checroun, J. Susini, P. Dumas, P. Tchoreloff, M. Besnard, P. Walter, Kinetics of oil saponification by lead salts in ancient preparations of pharmaceutical lead plasters and painting lead mediums. Talanta **70**, 1136–1142 (2006). https://doi.org/10.1016/j.talanta.2006.03.007

368. R.J. Gettens, H. Kühn, W.T. Chase, 3. Lead White. Stud. Conserv. **12**, 125–139 (1967). https://doi.org/10.1179/sic.1967.013

369. P. Walter, P. Martinetto, G. Tsoucaris, R. Bréniaux, M.A. Lefebvre, G. Richard, J. Talabot, E. Dooryhee, Making make-up in Ancient Egypt. Nature **397**, 483–484 (1999). https://doi.org/10.1038/17240

370. P. Martinetto, M. Anne, E. Dooryhée, M. Drakopoulos, M. Dubus, J. Salomon, A. Simionovici, P. Walter, Synchrotron X-ray micro-beam studies of ancient Egyptian make-up. Nucl. Instrum. Methods Phys. Res. B **181**, 744–748 (2001). https://doi.org/10.1016/S0168-583X(01)00383-4

371. T. Christiansen, M. Cotte, W. de Nolf, E. Mouro, J. Reyes-Herrera, S. de Meyer, F. Vanmeert, N. Salvadó, V. Gonzalez, P.E. Lindelof, K. Mortensen, K. Ryholt, K. Janssens, S. Larsen, Insights into the composition of ancient Egyptian red and black inks on papyri achieved by synchrotron-based microanalyses. Proc. Natl. Acad. Sci. U S A **117**, 27825–27835 (2020). https://doi.org/10.1073/pnas.2004534117

372. K.J. van den Berg, P. Noble, J. Wadum, K. Groen, R. Heeren, Aspects of 17th century Binding Medium: inclusions in Rembrandt’s Anatomy Lesson of Dr Nicolaes Tulp, in: Proceedings of the
International Congress on Contribution of Chemistry to the Works of Art, Art & Chimie, La Couleur, eds. By G. Jacques, M. Jean-Pierre (CNRS Editions, Paris, 2000), pp. 126–129

373. E. Kotulanová, P. Bezdička, D. Hradil, J. Hradilová, S. Švarcová, T. Grygar, Degradation of lead-based pigments by salt solutions. J. Cult. Herit. **10**, 367–378 (2009). https://doi.org/10.1016/j.culher.2008.11.001

374. M. Niknejad, A.H. Karimy, Lead White or Lead Whites? Reconsideration of Methods of sefidāb-i-sorb Production in Iran. Stud. Conserv. **64**, 1–9 (2019). https://doi.org/10.1080/00393630.2018.1457290

375. I. Tapsoba, S. Arbault, P. Walter, C. Amatore, Finding out Egyptian Gods' secret using analytical chemistry: biomedical properties of Egyptian black makeup revealed by amperometry at single cells. Anal. Chem. **82**, 457–460 (2010). https://doi.org/10.1021/ac902348g

376. I. Costantini, P.P. Lottici, D. Bersani, D. Pontiroli, A. Casoli, K. Castro, J.M. Madariaga, Darkening of lead- and iron-based pigments on late Gothic Italian wall paintings: Energy dispersive X-ray fluorescence, μ-Raman, and powder X-ray diffraction analyses for diagnosis: Presence of β-PbO₂ (plattnerite) and α-PbO₂ (scrutinyite). J. Raman Spectrosc. **51**, 680–692 (2020). https://doi.org/10.1002/jrs.5817

377. M. Vagnini, R. Vivani, A. Sgamellotti, C. Miliani, Blackening of lead white: study of model paintings. J. Raman Spectrosc. **51**, 1118–1126 (2020). https://doi.org/10.1002/jrs.5879

378. S.M. Lussier, G.D. Smith, A review of the phenomenon of lead white darkening and its conversion treatment. Stud. Conserv. **52**, 41–53 (2007). https://doi.org/10.1179/sic.2007.52.supplement-1.41

379. E. Gliozzo, C. Ionescu, Pigments—Lead-based whites, reds, yellows and oranges and their alteration phases. Archaeol. Anthropol. Sci. **14**, 17 (2022). https://doi.org/10.1007/s12520-021-01407-z

380. R. Přikryl, J. Svobodová, K. Zák, D. Hradil, Anthropogenic origin of salt crusts on sandstone sculptures of Prague's Charles Bridge (Czech Republic): Evidence of mineralogy and stable isotope geochemistry. Eur. J. Mineral. **16**, 609–617 (2004). https://doi.org/10.1127/0935-1221/2004/0016-0609

381. J. Sterpenich, Cristallochimie des produits d'altération des vitreaux médiévaux: application au vieillissement des déchets vitrifiés. Bull. Eng. Geol. Env. **61**, 179–193 (2002)

382. M. Cotte, J. Susini, V.A. Solé, Y. Taniguchi, J. Chillida, E. Checroun, P. Walter, Applications of synchrotron-based micro-imaging techniques to the chemical analysis of ancient paintings. J. Anal. At. Spectrom. **23**, 820–828 (2008). https://doi.org/10.1039/b801358f

383. A. van Loon, P. Noble, A. Krekeler, G. Snickt, K. Janssens, Y. Abe, I. Nakai, J. Dik, Artificial opment, a new pigment in Rembrandt's palette. Herit Sci **5**, 26 (2017). https://doi.org/10.1186/s40494-017-0138-1

384. F. Vanmeert, N. De Keyser, A. Van Loon, L. Klaassen, P. Noble, K. Janssens, Transmission and reflection mode macroscopic X-ray powder diffraction imaging for the noninvasive visualization of paint degradation in still life paintings by Jan Davidsz. de Heem. Anal. Chem. **91**, 7153–7161 (2019). https://doi.org/10.1021/acs.analchem.9b00328

385. A. Van Loon, P. Noble, J. Boon, White hazes and surface crusts in Rembrandt's Homer and related paintings, in: ICOM Committee for Conservation 16th Triennial Meeting Lisbon Portugal 19–23 September 2011 (Critério Artes Gráficas, Lda. and ICOM Committee for Conservation, 2011), n. 416

386. A. van Loon, P. Noble, J.J. Boon, The formation of complex crusts in oil paints containing lead white and smalt, in *Historical Technology, Materials and Conservation: SEM and Microanalysis*. ed. by B.N. Meeks (Archetype Publications Ltd, London, 2012), pp. 207–209

387. G. Albertson, A. Krekeler, A. van Loon, A.P. Gaibor, P. Noble, The blues of Jan de Bray's Judith and Holofernes: A technical study of two blue pigments and its impact on treatment. J. Am. Inst. Conserv. **58**, 217–232 (2019). https://doi.org/10.1080/01971360.2019.1643628

388. J.J. Boon, E. Oberthaler, Mechanical weakness and chemical reactivity observed in the paint structure and surface of The Art of Painting by Vermeer, in: Vermeer, Die Malkunst – Spurensicherung an Einem Meisterwerk: Ausstellungskatalog Des Kunsthistorischen Museums Wien, eds. By S. Haag, E. Oberthaler, S. Penot (Residenz Verlag, Wien, 2010), pp. 235–253, 328–335

389. J.J. Boon, Chemistry Underneath the Painting Surface: Palermiterie Formation in/on a Painting by Johannes Vermeer and by Jacob Jordaens using Laboratory- and Synchrotron-aided Spectroscopic Methods. Microsc. Microanal. **19**, 1408–1409 (2013). https://doi.org/10.1017/s1431927613009033

390. D. Hradil, T. Grygar, J. Hradilová, P. Bezdička, V. Grunwaldová, I. Fogaš, C. Miliani, Microanalytical identification of Pb-Sb-Sn yellow pigment in historical European paintings and its differentiation from lead tin and Naples yellows. J. Cult. Herit. **8**, 377–386 (2007). https://doi.org/10.1016/j.culher.2007.07.001
391. H. Stege, Out of the blue? Considerations on the early use of smalt as blue pigment in European easel painting. Zeitschrift Für Kunsttechnologie Und Konservierung: ZKK 18, 121–142 (2004)

392. F. Delamare, Blue Pigments: 5000 Years of Art and Industry (Archetype Publications Ltd, London, 2013)

393. G. Cavallo, M.P. Riccardi, Glass-based pigments in painting: smalt blue and lead-tin yellow type II. Archaeol. Anthropol. Sci. 13, 199 (2021). https://doi.org/10.1007/s12520-021-01453-7

394. J. Riederer, Die Smalte. Deutsche Farbenzeitschrift 22, 386–395 (1968)

395. Z. Zlámalová Čílová, M. Gelnar, S. Randáková, Smalt production in the Ore Mountains: Characterization of samples related to the production of blue pigment in Bohemia. Archaeometry 62, 1202–1215 (2020). https://doi.org/10.1111/arcm.12584

396. J. Molera, A. Climent-Font, G. Garcia, T. Pradell, O. Vallcorba, A. Zucchiatti, Experimental study of historical processing of cobalt arsenide ore for colouring glazes (15–16th century Europe). J. Archaeol. Sci. Rep. 36, 102797 (2021). https://doi.org/10.1016/j.jasrep.2021.102797

397. M. Spring, V. Kugler, S. Bean, Quantitative energy dispersive X-ray analysis of the blue pigment smalt, in: Historical Technology, Materials and Conservation: SEM and Microanalysis, eds. By N. Meek, C. Cartwright, A. Meek, A. Mongiatti (Archetype Publications Ltd, London, 2012), pp. 114–122

398. S. Panighello, A. Kavčič, K. Vogel-Mikuš, N.H. Tennent, A. Wallert, S.B. Hočevar, J.T. van Elteren, Investigation of smalt in cross-sections of 17th century paintings using elemental mapping by laser ablation ICP-MS. Microchem. J. 125, 105–115 (2016). https://doi.org/10.1016/j.microc.2015.11.015

399. D. Spring, M. Von Aderkas, N. Rukavina, F. Peggie, An astronomer by ferdinand bol: materials, colour change and conservation. Natl. Gallery Tech. Bull. 38, 76–96 (2017)

400. A. van Loon, P. Noble, D. de Man, M. Alfeld, T. Callewaert, G. Van der Snickt, K. Janssens, J. Dik, The role of smalt in complex pigment mixtures in Rembrandt's Homer 1663: combining MA-XRF imaging, microanalysis, paint reconstructions and OCT. Herit. Sci. 8, 90 (2020). https://doi.org/10.1186/s40494-020-00429-5

401. N. von Aderkas, N. Daly, R. Billinge, A. van Loon, J. Dik, Using macro-XRF to examine Rembrandt's Portrait of Frederik Rihel on Horseback: new insights on pigment distribution and a hidden portrait, in: Rembrandt Now, Technical Practice, Conservation and Research, eds. By M. Spring, A. Roy (The National Gallery, Archetype Publications Ltd, London, 2022), pp. 126–137

402. M. Alfeld, C. Laurenze-Landsberg, A. Denker, K. Janssens, P. Noble, Neutron activation autoradiography and scanning macro-XRF of Rembrandt van Rijn's Susanna and the Elders (Gemäldegalerie Berlin): a comparison of two methods for imaging of historical paintings with elemental contrast. Appl. Phys. A Mater. Sci. Process. 119, 795–805 (2015). https://doi.org/10.1007/s00339-015-9081-8

403. C. Laurenze-Landsberg, The examination of paintings by rembrandt with neutron autoradiography and a comparison of neutron autoradiography with scanning macro-XRF. Restaurierung Und Archäologie 8, 99–114 (2015). https://doi.org/10.11588/ra.2015.0.37028

404. J. Plesters, A preliminary note on the incidence of discolouration of smalt in oil media. Stud. Conserv. 14, 62–74 (1969). https://doi.org/10.1179/sic.1969.006

405. M. Spring, N. Penny, R. White, M. Wyld, Colour change in "The Conversion of the Magdalen" attributed to Pedro Campaña. Natl. Gallery Tech. Bull. 22, 54–63 (2001)

406. M. Spring, C. Higgitt, D. Saunders, Investigation of pigment-medium processes in oil paint containing degraded smalt. Natl. Gallery Tech. Bull. 26, 56–70 (2005)

407. J. Carter, A. van Loon, K. Keune, E. Froment, From purple to brown: Using degradation products in reconstructions of a complex smalt paint mixture in The Night Watch to study color change, in Working towards a Sustainable Past: ICOM-CC 20th Triennial Conference Preprints, Valencia, 18–22 September 2023, ed. by B.J. Bridgland (International Council of Museums, Paris, 2023), pp.1–9

408. F. Abraham, A. Vandivere, S. Meloni, A. van Loon, Purple with a purpose: Investigating and reconstructing the discoloured skirt in Frans Hals's Portrait of Aletta Hanemans, in: Bridging the Gap - Synergies between Art History and Conservation, eds. By B. Sauge, T. Ford, T. Froysaker, K. J. van den Berg (Archetype Publications, London, 2024)

409. J.J. Boon, K. Keune, J. Van Der Weerd, M. Geldof, J.R.J. Van Asperen De Boer, Imaging microscopic, secondary ion mass spectrometric and electron microscopic studies on discoloured and partially discoloured smalt in cross-sections of 16th century paintings. Chimia (Aarau) 55, 952–960 (2001). https://doi.org/10.2533/chimia.2001.952

410. L. Robinet, M. Spring, S. Pagès-Camagna, Vibrational spectroscopy correlated with elemental analysis for the investigation of smalt pigment and its alteration in paintings. Anal. Methods 5, 4628–4638 (2013). https://doi.org/10.1039/c3ay40906f
411. N. Eastaugh, V. Walsh, T. Chaplin, R. Siddal, The pigment compendium: a dictionary of historical pigments (Elsevier Butterworth-Heinemann, Oxford and Burlington, 2004)

412. S. Švarcová, D. Hradil, J. Hradilová, Z. Čermáková, Pigments—copper-based greens and blues. Archaeol. Anthropol. Sci. **13**, 190 (2021). https://doi.org/10.1007/s12520-021-01406-0

413. D. A. Scott, Copper and Bronze in Art. Corrosion, Colorants, Conservation (The Getty Conservation Institute, Los Angeles, 2002)

414. S. Schiegl, K.L. Weiner, A. El Goresy, Discovery of copper chloride cancer in ancient Egyptian polychromic wall paintings and faience: a developing archaeological disaster. Naturwissenschaften **76**, 393–400 (1989). https://doi.org/10.1007/BF00366160

415. M. Nicola, R. Gobetto, A. Masic, Egyptian blue, Chinese blue, and related two-dimensional silicates: from antiquity to future technologies. Part A: general properties and historical uses. Rend. Lincei. **34**, 369–413 (2023). https://doi.org/10.1007/s12210-023-01153-5

416. S. Pagès-Camagna, I. Reiche, C. Brouder, D. Cabaret, S. Rossano, B. Kanngießer, A. Erko, New insights into the colour origin of archaeological Egyptian blue and green by XAFS at the Cu K-edge. X-Ray Spectrom. **35**, 141–145 (2006). https://doi.org/10.1002/xrs.885

417. D. Lau, P. Kappen, M. Strohschnieder, N. Brack, P.J. Pigram, Characterization of green copper phase pigments in Egyptian artifacts with X-ray absorption spectroscopy and principal components analysis. Spectrochim. Acta Part B At. Spectrosc. **63**, 1283–1289 (2008). https://doi.org/10.1016/j.sab.2008.09.013

418. A. Lluveras, A. Torrents, P. Giráldez, M. Vendrell-Saz, Evidence for the use of Egyptian Blue in an 11th century mural altarpiece by sem-eds, FTIR and SR XRD (Church Of Sant Pere, Terrassa, Spain). Archaeometry **52**, 308–319 (2010). https://doi.org/10.1111/j.1475-4754.2009.00481.x

419. C. Calza, M.J. Anjos, S.M.F. Mendonça De Souza, A. Brancaglion, R.T. Lopes, X-ray microfluorescence with synchrotron radiation applied in the analysis of pigments from ancient Egypt. Appl. Phys. A Mater. Sci. Process. **90**, 75–79 (2008). https://doi.org/10.1007/s00339-007-4234-z

420. T. Pradell, N. Salvado, G.D. Hatton, M.S. Tite, Physical processes involved in production of the ancient pigment, Egyptian blue. J. Am. Ceram. Soc. **89**, 1426–1431 (2006). https://doi.org/10.1111/j.1551-2916.2005.00904.x

421. J. Bredal-Jørgensen, J. Sanyova, V. Rask, M.L. Sargent, R.H. Therkildsen, Striking presence of Egyptian blue identified in a painting by Giovanni Battista Benvenuto from 1524. Anal. Bioanal. Chem. **401**, 1433–1439 (2011). https://doi.org/10.1007/s00216-011-5140-y

422. A. Sgamellotti, C. Anselmi, An evergreen blue. Spectroscopic properties of Egyptian blue from pyramids to Raphael, and beyond. Inorganica Chim Acta **530**, 120699 (2022). https://doi.org/10.1016/j.ica.2021.120699

423. C. Anselmi, M. Vagnini, C. Seccaroni, M. Azzarelli, T. Frizzi, R. Alberti, M. Falcioni, A. Sgamellotti, Imaging the antique: unexpected Egyptian blue in Raphael’s Galatea by non-invasive mapping. Rendiconti Lincei **31**, 913–917 (2020). https://doi.org/10.1007/s12210-020-00960-4

424. S. Švarcová, Z. Čermáková, J. Hradilová, P. Bezdička, D. Hradil, Non-destructive micro-analytical differentiation of copper pigments in paint layers of works of art using laboratory-based techniques. Spectrochim Acta A Mol. Biomol. Spectrosc. **132**, 514–525 (2014). https://doi.org/10.1016/j.saa.2014.05.022

425. C. Conti, J. Striova, I. Aliatis, E. Possenti, G. Massonnet, C. Muehlethaler, T. Poli, M. Positano, The detection of copper resinate pigment in works of art: Contribution from Raman spectroscopy. J. Raman Spectrosc. **45**, 1186–1196 (2014). https://doi.org/10.1002/jrs.4455

426. C. Paz, L.R. Rodriguez-Simón, E. Manzano, Spectroscopic study of mixtures of green copper pigments in fresh and aged model samples. Case studies on masterpieces from the Spanish Golden Age. J. Cult. Herit. **59**, 217–230 (2023). https://doi.org/10.1016/j.culher.2022.12.004

427. J. Xu, Y. Kuang, B. Zhang, Y. Liu, D. Fan, W. Zhou, H. Xie, High-pressure study of azurite $Cu_3(CO_3)_2(OH)_2$ by synchrotron radiation X-ray diffraction and Raman spectroscopy. Phys. Chem. Miner. **42**, 805–816 (2015). https://doi.org/10.1007/s00269-015-0764-7

428. G. Van Der Snickt, C. Miliani, K. Janssens, B.G. Brunetti, A. Romani, F. Rosi, P. Walter, J. Castaing, W. De Nolf, L. Klaassen, I. Labarque, R. Wittermann, Material analyses of “Christ with singing and music-making Angels”, a late 15th-C panel painting attributed to Hans Memling and assistants: Part I. non-invasive in situ investigations. J. Anal. At. Spectrom. **26**, 2216–2229 (2011). https://doi.org/10.1039/c1ja10073d
429. L.M. Smieska, R. Mullett, L. Ferri, A.R. Woll, Trace elements in natural azurite pigments found in illuminated manuscript leaves investigated by synchrotron X-ray fluorescence and diffraction mapping. Appl. Phys. A Mater. Sci. Process. **123**, 484 (2017). https://doi.org/10.1007/s00339-017-1093-0

430. E. Mattei, G. De Vivo, A. De Santis, C. Gaetani, C. Pelosi, U. Santamaria, Raman spectroscopic analysis of azurite blackening. J. Raman Spectrosc. **39**, 302–306 (2008). https://doi.org/10.1002/jrs.1845

431. Y. Cudennec, A. Lecerf, The transformation of Cu(OH)₂ into CuO, revisited. Solid State Sci. **5**, 1471–1474 (2003). https://doi.org/10.1016/j.solidstatesciences.2003.09.009

432. S. Rickerby, Heat alterations to pigments painted in the fresco technique. The Conservator **15**, 39–44 (1991). https://doi.org/10.1080/01410096.1991.9995063

433. A. Lluveras, S. Boularand, A. Andreotti, M. Vendrell-Saz, Degradation of azurite in mural paintings: Distribution of copper carbonate, chlorides and oxalates by SRFTIR. Appl. Phys. A Mater. Sci. Process. **99**, 363–375 (2010). https://doi.org/10.1007/s00339-010-5673-5

434. S. Švarcová, D. Hradil, J. Hradilová, E. Kočí, P. Bezdička, Micro-analytical evidence of origin and degradation of copper pigments found in Bohemian Gothic murals. Anal. Bioanal. Chem. **395**, 2037–2050 (2009). https://doi.org/10.1007/s00216-009-3144-7

435. E. Egel, S. Simon, Investigation of the painting materials in Zhongshan Grottoes (Shaanxi, China). Herit. Sci. **1**, 29 (2013). https://doi.org/10.1186/2050-7445-1-29

436. M.M. Naumova, S.A. Pisareva, A note on the use of blue and green copper compounds in paintings. Stud. Conserv. **39**, 277–283 (1994). https://doi.org/10.1179/sic.1994.39.4.277

437. B. Shui, Z. Yu, Q. Cui, Z. Wang, Z. Yin, M. Sun, B. Su, Blue pigments in Cave 256, Mogao Grottoes: a systematic analysis of murals and statues in Five dynasties, Song Dynasty and Qing Dynasty. Herit. Sci. **10**, 89 (2022). https://doi.org/10.1186/s40494-022-00722-5

438. Theophilus, On Divers Arts: The Foremost Medieval Treatise on Painting, Glassmaking, and Metalwork (Dover Publications, Incorporated, New York, 1979)

439. E. Bidaud, E. Halwax, E. Pantos, B. Sipek, Analyses of a green copper pigment used in a thirteenth-century wall painting. Stud. Conserv. **53**, 81–92 (2008). https://doi.org/10.1179/sic.2008.53.2.81

440. P. Richardin, V. Mazel, P. Walter, O. Lapré vote, A. Brunelle, Identification of different copper green pigments in renaissance paintings by cluster-TOF-SIMS imaging analysis. J. Am. Soc. Mass Spectrom. **22**, 1729–1736 (2011). https://doi.org/10.1007/s13361-011-0171-3

441. S. Valadas, R.V. Freire, A. Cardoso, J. Mirão, C.B. Dias, P. Vandenabeele, A. Candeias, On the Use of the Unusual Green Pigment Brochantite (Cu₄(SO₄)(OH)₆) in the 16th-Century Portuguese-Flemish Paintings Attributed to the Master Frei Carlos Workshop. Microsc. Microanal. **21**, 518–525 (2015). https://doi.org/10.1017/S1431927615000094

442. R.J. Gettens, The corrosion products of an ancient chinese bronze. J. Chem. Educ. **28**, 67–71 (1951). https://doi.org/10.1021/ed028p67

443. J. Buse, V. Otero, M.J. Melo, New insights into synthetic copper greens: the search for specific signatures by Raman and infrared spectroscopy for their characterization in medieval artworks. Heritage **2**, 1614–1629 (2019). https://doi.org/10.3390/Heritage2020099

444. M. San Andrés, J.M. De La Roja, V.G. Baonza, N. Sancho, Verdigris pigment: a mixture of compounds. Input from Raman spectroscopy. J. Raman Spectrosc. **41**, 1178–1186 (2010). https://doi.org/10.1002/jrs.2786

445. S. Švarcová, M. Klementová, P. Bezdička, W. Śasocha, M. Dušek, D. Hradil, Synthesis and characterization of single crystals of the layered copper hydroxide acetate Cu₂(OH)₃(CH₃COO)·H₂O. Cryst. Res. Technol. **46**, 1051–1057 (2011). https://doi.org/10.1002/crat.201100262

446. S. Bette, R.K. Kremer, G. Eggert, R.E. Dinnebier, On verdigris, Part II: Synthesis of the 2–1–5 phase, Cu₃(CH₃COO)₄(OH)₂·5H₂O, by long-term crystallisation from aqueous solution at room temperature. Dalton Trans. **47**, 8209–8220 (2018). https://doi.org/10.1039/c8dt01758a

447. C.C.R. Sutton, G. Da Silva, G.V. Franks, Modeling the IR spectra of aqueous metal carboxylate complexes: Correlation between bonding geometry and stretching mode wavenumber shifts. Chem. Eur. J. **21**, 6801–6805 (2015). https://doi.org/10.1002/chem.201406516

448. S.W.C. Horn, M. Lewis, M.R. Palmer, C.A. Bayse, Examination of the composition and mechanism of discoloration of the fugitive pigment copper resinate. Inorganica Chim Acta **504**, 119407 (2020). https://doi.org/10.1016/j.ica.2019.119407
449. M. Gunn, G. Chottard, E. Rivière, J.J. Girerd, J.C. Chottard, Chemical reactions between copper pigments and oleoresinous media. Stud. Conserv. **47**, 12–23 (2002). https://doi.org/10.1179/sic.2002.47.1.12

450. L. Osete-Cortina, M.T. Doménech-Carbó, Analytical characterization of diterpenoid resins present in pictorial varnishes using pyrolysis-gas chromatography-mass spectrometry with online trimethylsilylation. J. Chromatogr. **A** **1065**, 265–278 (2005). https://doi.org/10.1016/j.chroma.2004.12.078

451. E. Ioakimoglou, S. Boyatzis, P. Argitis, A. Fostiridou, K. Papapanagiotou, N. Yannovits, Thin-film study on the oxidation of linseed oil in the presence of selected copper pigments. Chem. Mater. **11**, 2013–2022 (1999). https://doi.org/10.1021/cm9806578

452. A. Zoppi, C. Lofrumento, N.F.C. Mendes, E.M. Castellucci, Metal oxalates in paints: A Raman investigation on the relative reactivities of different pigments to oxalic acid solutions. Anal. Bioanal. Chem. **397**, 841–849 (2010). https://doi.org/10.1007/s00216-010-3583-1

453. S. Boyatzis, E. Ioakimoglou, P. Argitis, UV exposure and temperature effects on curing mechanisms in thin linseed oil films: Spectroscopic and chromatographic studies. J. Appl. Polym. Sci. **84**, 936–949 (2002). https://doi.org/10.1002/app.10117

454. S. Prati, I. Bonacini, G. Sciutto, A. Genty-Vincent, M. Cotte, M. Eveno, M. Menu, R. Mazzeo, ATR-FTIR microscopy in mapping mode for the study of verdigris and its secondary products. Appl. Phys. A Mater. Sci. Process. **122**, 10 (2016). https://doi.org/10.1007/s00339-015-9519-z

455. K. J. van den Berg, M. H. van Eikema Hommes, K. M. Groen, J. J. Boon, B. H. Berrie, On copper green glazes in paintings, in: Proceedings of the International Congress on Contribution of Chemistry to the Works of Art, Art & Chimie, La Couleur, eds. By G. Jacques, M. Jean-Pierre (CNRS Editions, Paris, 2000), pp. 18–23

456. E. West Fitzhugh, Artists’ Pigments: A Handbook of Their History & Characteristics-Volume 3 (National Gallery of Art Washington & Oxford University Pres, Washington and Oxford, 1997)

457. X. Cheng, Y. Xia, Y. Ma, Y. Lei, Three fabricated pigments (Han purple, indigo and emerald green) in ancient Chinese artifacts studied by Raman microscopy, energy-dispersive X-ray spectrometry and polarized light microscopy. J. Raman Spectrosc. **38**, 1274–1279 (2007). https://doi.org/10.1002/jrs.1766

458. C. Herm, Emerald Green versus Scheele’s Green, in: Acta Artis Academia 2020: The Colour Theme, Proceedings of the 7th Interdisciplinary ALMA Conference 16th-18th October 2019 (Academy of Fine Arts in Prague -University Library Bratislava, Prague, 2020), pp. 189–202

459. L. Pantoja Munoz, Hidden in plain sight: revisiting the synthesis, characterisation, degradation and the intricate relationship between Scheele’s green and Emerald green. Herit. Sci. **12**, 94 (2024). https://doi.org/10.1186/s40494-024-01192-7

460. F. Rosi, C. Miliani, I. Borgia, B. Brunetti, A. Sgamellotti, Identification of nineteenth century blue and green pigments by in situ X-ray fluorescence and micro-Raman spectroscopy. J. Raman Spectrosc. **35**, 610–615 (2004). https://doi.org/10.1002/jrs.1180

461. S. Bahfenne, R.L. Frost, A review of the vibrational spectroscopic studies of arsenite, antimonite, and antimonate minerals. Appl. Spectrosc. Rev. **45**, 101–129 (2010). https://doi.org/10.1080/05704920903435839

462. O. Petrova, D. Pankin, A. Povolotckaia, E. Borisov, T. Krivul'ko, N. Kurganov, A. Kurochkin, Pigment palette study of the XIX century plafond painting by Raman spectroscopy. J. Cult. Herit. **37**, 233–237 (2019). https://doi.org/10.1016/j.culher.2018.11.010

463. S. Valadas, P. Vandenabeele, M. Gil, J.C. Frade, E. Vermeersch, S. Lycke, L. Dias, A. Candeias, M. Costa, Analysis of green pigments: The case of Almada Negreiros maritime station murals in Lisbon (Portugal). J. Raman Spectrosc. (2024). https://doi.org/10.1002/jrs.6717

464. M.P. Gil, E. Henderson, J. Burdge, E. Kotze, W. McCarthy, Detecting emerald green in 19thC book bindings using vis-NIR spectroscopy. Anal. Methods **15**, 6603–6609 (2023). https://doi.org/10.1039/d3ay01329d

465. D. Buti, F. Rosi, B.G. Brunetti, C. Miliani, In-situ identification of copper-based green pigments on paintings and manuscripts by reflection FTIR. Anal. Bioanal. Chem. **405**, 2699–2711 (2013). https://doi.org/10.1007/s00216-013-6707-6

466. Z. Li, L. Wang, H. Chen, Q. Ma, Degradation of emerald green: scientific studies on multi-polychrome Vairocana Statue in Dazu Rock Carvings, Chongqing, China. Herit. Sci. **8**, 64 (2020). https://doi.org/10.1186/s40494-020-00410-2
467. P. Holakooei, A.H. Karimy, G. Nafisi, Lammerite as a Degradation Product of Emerald Green: Scientific Studies on a Rural Persian Wall Painting. Stud. Conserv. **63**, 391–402 (2018). https://doi.org/10.1080/00393630.2017.1419658

468. K.P. Smith, G. Ólafsson, All that glitters is not gold: Multi-instrumental identification of Viking Age orpiment (As₂S₃) from Surtshellir cave, Iceland. J. Archaeol. Sci. Rep. **47**, 103724 (2023). https://doi.org/10.1016/j.jasrep.2022.103724

469. E. Gliozzo, L. Burgio, Pigments—Arsenic-based yellows and reds. Archaeol. Anthropol. Sci. **14**, 4 (2022). https://doi.org/10.1007/s12520-021-01431-z

470. P. Knipe, K. Eremin, M. Walton, A. Babini, G. Rayner, Materials and techniques of Islamic manuscripts. Herit. Sci. **6**, 55 (2018). https://doi.org/10.1186/s40494-018-0217-y

471. V.S.F. Muralha, C. Miguel, M.J. Melo, Micro-Raman study of Medieval Cistercian 12–13th century manuscripts: Santa Maria de Alcobaça, Portugal. J. Raman Spectrosc. **43**, 1737–1746 (2012). https://doi.org/10.1002/jrs.4065

472. Y. Oubelkacem, T. Lamhasni, A. El Bakkali, S.A. Lyazidi, M. Haddad, A. Ben-Ncer, Parchments and coloring materials in two IXth century manuscripts: On-site non-invasive multi-techniques investigation. Spectrochim Acta A Mol. Biomol. Spectrosc. **247**, 119093 (2021). https://doi.org/10.1016/j.saa.2020.119093

473. M. Vermeulen, L. Burgio, N. Vandeperre, E. Driscoll, M. Viljoen, J. Woo, M. Leona, Beyond the connoisseurship approach: creating a chronology in Hokusai prints using non-invasive techniques and multivariate data analysis. Herit. Sci. **8**, 62 (2020). https://doi.org/10.1186/s40494-020-00406-y

474. M. Vermeulen, M. Leona, Evidence of early amorphous arsenic sulfide production and use in Edo period Japanese woodblock prints by Hokusai and Kunisada. Herit. Sci. **7**, 73 (2019). https://doi.org/10.1186/s40494-019-0318-2

475. M. Vermeulen, J. Sanyova, K. Janssens, Identification of artificial orpiment in the interior decorations of the Japanese tower in Laeken, Brussels, Belgium. Herit. Sci. **3**, 9 (2015). https://doi.org/10.1186/s40494-015-0040-7

476. Y. Luo, E. Basso, H.D. Smith, M. Leona, Synthetic arsenic sulfides in Japanese prints of the Meiji period. Herit. Sci. **4**, 17 (2016). https://doi.org/10.1186/s40494-016-0087-0

477. S. Zaleski, Y. Takahashi, M. Leona, Natural and synthetic arsenic sulfide pigments in Japanese wood-block prints of the late Edo period. Herit. Sci. **6**, 32 (2018). https://doi.org/10.1186/s40494-018-0195-0

478. G. Grundmann, M. Richter, Types of dry-process artificial arsenic sulphide pigments in cultural heritage. Fatto d'archimia: Los Pigmentos Artificiales En Las Técnicas Pictóricas, 119–144 (2012)

479. G. Grundmann, M. Richter, Current research on artificial arsenic sulphide pigments in artworks: A short review. Chimia (Aarau) **62**, 903–907 (2008). https://doi.org/10.2533/chimia.2008.903

480. M. Vermeulen, K. Palka, M. Vlček, J. Sanyova, Study of dry- and wet-process amorphous arsenic sulfides: Synthesis, Raman reference spectra, and identification in historical art materials. J. Raman Spectrosc. **50**, 396–406 (2019). https://doi.org/10.1002/jrs.5534

481. G. Grundmann, C. Rötter, Artificial orpiment: Microscopic, diffractometric and chemical characteristics of synthesis products in comparison to natural orpiment, in: Auripigment: Studien Zu Dem Mineral Und Den Künstlichen Produkten (Siegl, München, 2007), pp. 105–140

482. J. Pérez-Arantegui, E. Ribechini, M.P. Colombini, F. Escudero, Characterization of an ancient “chemical” preparation: Pigments and drugs in medieval Islamic Spain. J. Archaeol. Sci. **38**, 3350–3357 (2011). https://doi.org/10.1016/j.jas.2011.07.021

483. A.J. Cruz, H.P. Melo, S. Valadas, C. Miguel, A. Candeias, The Matter from Which an Orange Colour Is Made: On the Arsenic Pigment Used in a Portuguese Mannerist Painting. Heritage **5**, 2646–2660 (2022). https://doi.org/10.3390/heritage5030138

484. M. Vermeulen, S. Saverwyns, A. Coudray, K. Janssens, J. Sanyova, Identification by Raman spectroscopy of pararealgar as a starting material in the synthesis of amorphous arsenic sulfide pigments. Dyes Pigm. **149**, 290–297 (2018). https://doi.org/10.1016/j.dye pig.2017.10.009

485. D.L. Douglass, Chichang Shing, Ge Wang, The light-induced alteration of realgar to pararealgar. Am. Miner. **77**, 1266–1274 (1992)

486. K. Trentelman, L. Stodulski, M. Pavlosky, Characterization of pararealgar and other light-induced transformation products from realgar by Raman microspectroscopy. Anal. Chem. **68**, 1755–1761 (1996). https://doi.org/10.1021/ac951097o
487. P. Bonazzi, L. Bindi, A crystallographic review of arsenic sulfides: Effects of chemical variations and changes induced by exposure to light. Zeitschrift Fur Kristallographie **223**, 132–147 (2008). https://doi.org/10.1524/zkri.2008.0011

488. P. Bonazzi, S. Menchetti, G. Pratesi, M. Muniz-Miranda, G. Sbrana, Light-induced variations in realgar and β-As₄S₄: X-ray diffraction and Raman studies. Am. Miner. **81**, 874–880 (1996). https://doi.org/10.2138/am-1996-7-810

489. A. Macchia, S. Nunziante Cesaro, L. Campanella, A. Maras, M. Rocchia, G. Roscioli, Which light for cultural heritage: Comparison of light sources with respect to realgar photodegradation. J. Appl. Spectrosc. **80**, 637–643 (2013). https://doi.org/10.1007/s10812-013-9820-6

490. F. Wu, Y. Zhang, Y. Li, Y. Wang, J. Ma, F. Wang, Photoinduced effects of monochromatic visible light with different wavelengths on realgar. J. Raman Spectrosc. **53**, 1533–1539 (2022). https://doi.org/10.1002/jrs.6408

491. D. Mahon, S.A. Centeno, M.T. Wypyski, X.F. Salomon, A. Bayer, Technical Study of Three Allegorical Paintings by Paolo Veronese: The Choice Between Virtue and Vice, Wisdom and Strength, and Mars and Venus united by Love (The Metropolitan Museum of Art and Yale University Press, New York and New Haven, 2010)

492. J. Dunkerton, H. Howard, Sebastiano del Piombo’s “Raising of Lazarus”: A History of Change. National Gallery Technical Bulletin **30**, 26–51 (2009)

493. J. Dunkerton, M. Spring, R. Billinge, K. Kalinina, R. Morrison, G. Macaro, D. Peggy, A. Roy, Titian’s Painting Technique to c1540. National Gallery Technical Bulletin **34**, 4–31 (2013). https://www.nati.onalgallery.org.uk/research/research-resources/technical-bulletin/technical-bulletin-volume-34

494. A.M. Correia, R.J.H. Clark, M.I.M. Ribeiro, M.L.T.S. Duarte, Pigment study by Raman microscopy of 23 paintings by the Portuguese artist Henrique Pousão (1859–1884). J. Raman Spectrosc. **38**, 1390–1405 (2007). https://doi.org/10.1002/jrs.1786

495. M.C. Corbeil, K. Helwig, An occurrence of pararealgar as an original or altered artists’ pigment. Stud. Conserv. **40**, 133–138 (1995). https://doi.org/10.1179/sic.1995.40.2.133

496. L. Burgio, R.J.H. Clark, K. Theodoraki, Raman microscopy of Greek icons: Identification of unusual pigments. Spectrochim Acta A Mol. Biomol. Spectrosc. **59**, 2371–2389 (2003). https://doi.org/10.1016/S1386-1425(03)00079-9

497. N. Penny, A. Roy, M. Spring, Veronese’s Paintings in the National Gallery, Techniques and Materials: Part II. Natl. Gallery Tech. Bull. **17**, 32–55 (1996)

498. D. Hradil, J. Hradilová, P. Bezdička, S. Švarcová, Z. Čermáková, V. Košařová, I. Němec, Crocoite PbCrO₄ and mimetite Pb₅(AsO₄)₃Cl: Rare minerals in highly degraded mediaeval murals in Northern Bohemia. J. Raman Spectrosc. **45**, 848–858 (2014). https://doi.org/10.1002/jrs.4556

499. R.J. Gettens, R.L. Feller, W.T. Chase, Vermilion and cinnabar. Stud. Conserv. **17**, 45–69 (1972). https://doi.org/10.1179/sic.1972.006

500. J. Martín-Gil, F.J. Martín-Gil, G. Delibes-de-Castro, P. Zapatero-Magdaleno, F.J. Sarabia-Herrero, The first known use of vermillion. Experientia **51**, 759–761 (1995). https://doi.org/10.1007/BF01922425

501. M. Vitruvius Pollio, The Architecture of Marcus Vitruvius Pollio, In Ten Books (Priestley and Weale, London, 1826)

502. R. Ling, Roman Painting (Cambridge University Press, Cambridge, 1991)

503. U. Pappalardo, The Splendor of Roman Wall Painting (Getty Publications, Los Angeles, 2009)

504. A. Dominguez-Vidal, M. Jose De La Torre-Lopez, R. Rubio-Domene, M.J. Ayora-Cañada, In situ noninvasive Raman microspectroscopic investigation of polychrome plasterworks in the Alhambra. Analyst **137**, 5763–5769 (2012). https://doi.org/10.1039/c2an36027f

505. J. Yu, W.S. Warren, M.C. Fischer, Visualization of vermilion degradation using pump-probe microscopy. Sci. Adv. **5**, eaaw3136 (2019). https://doi.org/10.1126/sciadv.aaw3136

506. A. Sodo, L. Tortora, P. Biocca, A. Casanova Municchia, E. Fiorin, M.A. Ricci, Raman and time of flight secondary ion mass spectrometry investigation answers specific conservation questions on Bosch painting Saint Wilgefortis Triptych. J. Raman Spectrosc. **50**, 150–160 (2019). https://doi.org/10.1002/jrs.5479

507. I. Istudor, A. Dina, G. Rosu, D. Seclaman, G. Niculescu, An Alteration Phenomenon of Cinnabar Red Pigment in the Mural Paintings from Sucevita. E-Conservation **2**, 24–33 (2007)

508. D. Chiriu, M. Pala, F.A. Pisu, G. Cappellini, P.C. Ricci, C.M. Carbonaro, Time through colors: a kinetic model of red vermilion darkening from Raman spectra. Dyes Pigm. **184**, 108866 (2021). https://doi.org/10.1016/j.dyeepig.2020.108866
509. S. Pérez-Diez, A. Larrañaga, J.M. Madariaga, M. Maguregui, Unraveling the role of the thermal and laser impacts on the blackening of cinnabar in the mural paintings of Pompeii. Eur. Phys. J. Plus **137**, 1184 (2022). https://doi.org/10.1140/epjp/s13360-022-03392-1

510. J.K. McCormack, The darkening of cinnabar in sunlight. Miner. Depos. **35**, 796-798 (2000). https://doi.org/10.1007/s001260050281

511. W. Anaf, K. Janssens, K. De Wael, Formation of metallic mercury during photodegradation/photodarkening of α-HgS: electrochemical evidence. Angewandte Chemie – Int. Ed. **52**, 12568–12571 (2013). https://doi.org/10.1002/anie.201303977

512. K. Elert, C. Cardell, Weathering behavior of cinnabar-based tempera paints upon natural and accelerated aging. Spectrochim Acta A Mol. Biomol. Spectrosc. **216**, 236–248 (2019). https://doi.org/10.1016/j.saa.2019.03.027

513. K. Elert, M. Pérez Mendoza, C. Cardell, Direct evidence for metallic mercury causing photo-induced darkening of red cinnabar tempera paints. Commun Chem **4**, 174 (2021). https://doi.org/10.1038/s4
2004-021-00610-2

514. M.K. Neiman, M. Balonis, I. Kakoulli, Cinnabar alteration in archaeological wall paintings: an experimental and theoretical approach. Appl. Phys. A Mater. Sci. Process. **121**, 915–938 (2015). https://doi.org/10.1007/s00339-015-9456-x

515. A.C. Wibowo, C.D. Malliakas, H. Li, C.C. Stoumpos, D.Y. Chung, B.W. Wessels, A.J. Freeman, M.G. Kanatzidis, An unusual crystal growth method of the chalcohalide semiconductor, β-Hg₃S₂Cl₂: A new candidate for hard radiation detection. Cryst. Growth Des. **16**, 2678–2684 (2016). https://doi.org/10.1021/acs.cgd.5b01802

516. S. Pérez-Diez, Red Cinnabar Blackening in the Mural Paintings of Pompeii: Volcanic Impact, Burial Environment and Atmospheric Exposure, PhD Thesis, Universidad del País Vasco UPV/EHU, 2022

517. R.L. Feller, Studies on the darkening of vermilion by light. Report Stud. History Art **1**, 99–111 (1967)

518. F.W. Dickson, G. Tunell, The stability relations of cinnabar and metacinnabar. Am. Miner. **44**, 471–487 (1959)

519. A.M.T. Bell, R.A.D. Pattrick, D.J. Vaughan, Structural evolution of aqueous mercury sulphide precipitates: energy-dispersive X-ray diffraction studies. Mineral. Mag. **74**, 85–96 (2010). https://doi.org/10.1180/minmag.2010.074.1.85

520. R.L. Feller, Artist's Pigments: a Handbook of their History and Characteristics, vol. 1 (National Gallery of Art, Washington, 1986)

521. M. Ghirardello, V. Otero, D. Comelli, L. Toniolo, D. Dellasega, L. Nessi, M. Cantoni, G. Valentini, A. Nevin, M.J. Melo, An investigation into the synthesis of cadmium sulfide pigments for a better understanding of their reactivity in artworks. Dyes Pigm. **186**, 108998 (2021). https://doi.org/10.1016/j.dyepig.2020.108998

522. G. Pfaff, Cadmium sulfide / selenide pigments, in: Antraquinonoid Pigments - Color Fundamentals (De Gruyter, Berlin and Boston, 2022), pp. 37–42. https://doi.org/10.1515/9783110588071-006

523. V. Gonzalez, D. Gourier, G. Wallez, T. Calligaro, A. Artesani, F. Rosi, A. Romani, C. Grazia, C. Miliani, L. Monico, D. Comelli, M. Ghirardello, Luminescent Inorganic Pigments Used in Ancient and Modern Times, in: Springer Series on Fluorescence (Springer, Cham., 2023), pp. 1–45. https://doi.org/10.1007/4243_2022_43

524. F. Rosi, C. Grazia, F. Gabrieli, A. Romani, M. Paolantoni, R. Vivani, B.G. Brunetti, P. Colomban, C. Miliani, UV-Vis-NIR and micro Raman spectroscopies for the non destructive identification of Cd₁-xZnxS solid solutions in cadmium yellow pigments. Microchem. J. **124**, 856–867 (2016). https://doi.org/10.1016/j.microc.2015.07.025

525. C. Grazia, F. Rosi, F. Gabrieli, A. Romani, M. Paolantoni, R. Vivani, B.G. Brunetti, P. Colomban, C. Miliani, UV-Vis-NIR and microRaman spectroscopies for investigating the composition of ternary CdS₁-xSex solid solutions employed as artists' pigments. Microchem. J. **125**, 279–289 (2016). https://doi.org/10.1016/j.microc.2015.11.008

526. M. Thoury, J.K. Delaney, E.R. De La Rie, M. Palmer, K. Morales, J. Krueger, Near-infrared luminescence of cadmium pigments: In situ identification and mapping in paintings. Appl. Spectrosc. **65**, 939–951 (2011). https://doi.org/10.1366/11-06230

527. A. Cesaratto, C. D'Andrea, A. Nevin, G. Valentini, F. Tassone, R. Alberti, T. Frizzi, D. Comelli, Analysis of cadmium-based pigments with time-resolved photoluminescence. Anal. Methods **6**, 130–138 (2014). https://doi.org/10.1039/c3ay41585f