## 2 Materials and Methods
### Analytical Techniques  
The pigment particle size was analysed using the Mastersizer 2000 LF (Malvern Instruments, Worcestershire, UK) laser particle size analyser. The samples were previously dispersed in alcohol. As for the aggregates, grain size distribution was determined using  
Figure 1: Fresco (F) and nano-silica-based chromatic reintegration (SB) mock-ups painted with (**a**) silicate-, (**b**) oxide-, (**c**) sulphide-, and (**d**) acetate-based pigment. (**e**) Not painted mock-ups without NE (FR-F) and with NE (FR-SB). See Table 1 for an explanation of the identification codes. the dry sieving method with different metal mesh opening sizes (0.063, 0.125, 0.250, 0.500, 0.800, 1, 1.6, 2, 3.15, and 4 mm) according to European standards [25]. The mineralogical composition of the pigments, aggregates and lime was determined using X-ray diffraction (XRD, XPert PRO PANalytical B.V., Almelo, The Netherlands) according to the random-powder method. Analyses were performed using Cu-K\(\alpha\) radiation, Ni filter, 45 kV voltage, and 40 mA intensity. The exploration range was 3\({}^{\circ}\) to 60\({}^{\circ}\) 20 and the goniometer speed was 0.05\({}^{\circ}\) 20 s\({}^{-1}\). The oriented aggregate method was also used to properly identify the phyllosilicates in the GE-G sample [26; 27]. The mock-up surfaces were characterised by XRD grazing incidence (XPert PRO PANalytical B.V.) under the same conditions. The mineral phases were identified using the XPert HighScore software (version 4.9.0.27512). The molecular compositions of the raw materials (lime, aggregates, NE, and pigments) and the mock-ups were obtained by Attenuated Transmittance Reflectance Fourier-Transform Infrared Spectroscopy (ATR-FTIR) using a Thermo Nicolet 6700 (Thermo Fisher, Waltham, MA, USA) at a 2 cm\({}^{-1}\) resolution over 100 scans in the mid-infrared spectral region (400-4000 cm\({}^{-1}\)). For the test, samples were pressed with the plunger against a diamond crystal. For CIN-R, VER-R, and MAR-R (pigments and mock-ups), FTIR spectra were also taken in the far (50-400 cm\({}^{-1}\)) infrared spectral region where IR bands characteristic of sulphur and oxides appear. The elemental composition of the pigments was determined by X-ray fluorescence (XRF) with an Olympus Vanta C Handheld XRF analyser (Hamburg, Germany) in 'GeoChem' mode, using 3 beams working at 40, 10, and 50 kV, respectively. The total measurement time was 60 s: 20 s for each beam. Element recognition was obtained by means of the supplier's database. The equipment was used to identify chemical elements of atomic number greater than 12. As no specific calibration was applied apart from the default calibration of the equipment, the composition obtained is semi-quantitative. Aggregate elemental characterisation was also carried out by XRF using a S4 PIONEER-BRUKER (Billerica, MA, USA) wavelength dispersive X-ray fluorescence spectrometer, with a Rh tube (60 kV; 150 mA), LIF200/PET/OVO-55 analyser crystals and gas-flow proportional and scintillation detectors. The samples were ground and dispersed in potassium bromide tablets before the analysis. Measurements were taken in a vacuum, with the samples in rotation, in order to obtain the content in major elements (expressed as oxides), (Zetium, PANalytical). The pigment and aggregate microtexture and elemental composition were studied using a FEI Quanta400 environmental scanning electron microscopy (Hillsboro, OR, USA) with energy-dispersive X-ray spectroscopy (EDS) in both secondary (SE) and backscattered electron (BSE) detection modes. Observation conditions included a working distance of \(\sim\)10 mm, an accelerating potential of 20 kV and a specimen current of \(\sim\)60 mA. The microtexture and elemental composition of the mock-ups were studied with a JEOL JSM 6010 LA microscope (Tokyo, Japan) under the same conditions. The samples were studied by observing the surface directly, and by studying the paint layer in cross-sections.