## 2 Materials and Methods
### Analytical Techniques
For this, the specimens were embedded in epoxy resin (EpoThin 2 Epoxy Resin and EpoThin 2 Epoxy Hardener) and then cut and polished to a mirror finish. The colour of the painted mock-ups was characterised using CIELAB and CIELCH colour spaces [28; 29], measuring L* (lightness), a* and b* (colour coordinates), and C*ab (chroma) values using a Konica Minolta CM-700d spectrophotometer (Tokyo, Japan). L* represents lightness, varying from 0 (black) to 100 (white). The other two parameters are chromaticity coordinates: \(a^{*}\) goes from red to green (where +\(a^{*}\) is red and \(-a^{*}\) is green) and \(b^{*}\) from yellow to blue (+\(b^{*}\) is yellow and \(-b^{*}\) is blue). C*ab is calculated according to the following formula: C*ab = (a\({}^{2}\) + b\({}^{2}\))\({}^{1/2}\). The measurements were made in the specular component excluded (SCE) mode, for a spot diameter of 8 mm, using illuminant D65 at an observer angle of 10\({}^{\circ}\). A total of fifteen measurements were made for each mock-up and their average values and standard deviations (STDs) were computed. Colour parameters were also measured for the pigment powders after first flattening them against a glass support to obtain a smooth surface. \(\Delta\)L*, \(\Delta\)a*, \(\Delta\)b*, and \(\Delta\)C*\({}_{\text{ab}}\) colour differences and the total colour difference (\(\Delta\)E*\({}_{\text{ab}}\)) [28,29] were calculated in order to compare the colour of each pigment with (i) its corresponding fresco paint colour (F) and (ii) its corresponding chromatic reintegration (SB). The colour differences between F and SB were also calculated. The gloss of the mock-ups was measured with a Novo-Gloss Lite 20/60/85\({}^{\circ}\) glossmeter (Neurtek, Basque Country, Spain), with a reflection angle of 60\({}^{\circ}\), following the relevant Spanish standard [30]. The gloss parameter expresses the way the mock-ups reflect the light and, in particular, the way light is reflected by the painted surface at and near the specular direction [31]. Five measurements were taken per sample, and their average value and standard deviation (STD) were calculated. The surface hydrophobicity of the mock-ups was evaluated using a Phoenix-300 Touch SEO goniometer (KROMTEK, London, UK), with an outer diameter of 0.012\({}^{\prime\prime}\) (0.3048 mm) and an inner diameter needle of 0.005\({}^{\prime\prime}\) (0.127 mm). Measurements were carried out with 3 drops of 8 \(\mu\)L per mock-up following the relevant Spanish standard [32]. Average values and standard deviations (STDs) were computed. The roughness of the mock-ups was measured with a Mitutoy SJ400 (Mitutoyo, Kanagawa, Japan) profilometer that measures the arithmetic average roughness (Ra, \(\mu\)m) [33] over a distance of 2 cm. For each sample, 3 profiles were obtained, and the Ra average values were calculated, together with their corresponding standard deviations (STDs). The adhesion of the paint layer was studied by carrying out peeling tests using a double-sided Tesa Powerbond adhesive tape, which was applied and removed 3 times consecutively on each paint mock-up (fresco and reintegration). The weight of the peeled-off material was determined by calculating the difference in the weight (mg) of the tape before and after application, in line with [34]. The texture and appearance of the mock-ups were studied with a Nikon SMZ 1000 microscope (Melville, NY, USA). Cross-sections were studied under Polarised-Light Microscopy (PLM), in both plane-polarised (PPL) and cross-polarised (XPL) light modes.