## 2 Materials and Methods
### Samples
#### 2.1.2 Lacunae, Retouched and Restored Areas  
Six samples were collected from Panels A, D and E, and the sampling points are shown in Figure 3. Table 2 reports a short description and visible images of the samples. Given the complexity of the pictorial fragments, which showed the co-presence of layers attributable to both original (or relatively ancient) work and subsequent restoration interventions, samples were divided into two aliquots. The first aliquot was analysed using GC-MS for the identification of lipid, terpenoid and waxy fractions, by means of an analytical procedure based on one-spot hydrolysis and transesterification [16; 17]. The other aliquot was analysed with Py-GC-MS to verify the presence of proteinaceous and polysaccharide material [18] and detect synthetic polymers. In particular, analytical pyrolysis was carried out in combination with tetramethylammonium hydroxide (TMAH) to favour the detection of some organic binders by means of thermally assisted hydrolysis and methylation [19; 20]. \begin{table}
\begin{tabular}{c c c c} \hline
**Sample** & **Area** & **Description** & **Aim of the Investigations** \\ \hline \multirow{6}{*}{SG\_30} & \multirow{6}{*}{Panel E} & Fragments of white plaster + greyish & \multirow{6}{*}{Identification of the degraded protective} \\  & & pictorial finish taken from an area which & & \\  & & under UV appears characterized by an & & \\  & & uneven yellowish response. & & \\  & & Macroscopically, the surface appears & & \\  & & chromatically altered (with a spotted effect). & & \\ \hline \multirow{2}{*}{SG\_34} & \multirow{2}{*}{Panel E} & Fragments of white plaster + grayish paint & \multirow{2}{*}{Identification of altered protective} \\  & & finish taken from an area that shows no & & \\  & & fluorescence response under UV. & & \\  & & Macroscopically, the surface appears glossy. & & \\ \hline \multirow{2}{*}{SG\_37c} & \multirow{2}{*}{Vault, top part} & Gray pictorial spread on a layer of degraded & \multirow{2}{*}{Identification of organic binders} \\  & & plaster, taken from a degraded area due to & & \\  & & detachments and lifting of the surface layers. & & \\ \hline \multirow{2}{*}{SG\_41C} & \multirow{2}{*}{Vault, top part} & Purplish pictorial spread on a layer of & \multirow{2}{*}{Identification of organic binders} \\  & & degraded plaster, taken from a degraded & & \\  & & area with lifting of the surface layers. & & \\ \hline \multirow{6}{*}{SG\_43} & \multirow{6}{*}{Vault, top part} & Relief layer of material of an organic nature & \multirow{2}{*}{Identification of organic binders} \\  & & selectively taken from the pictorial surface. & & \\  & & These are tablets to simulate the golden & & \\  & & decorations of the halos and robes of the & & \\  & & [PERSON] (or relief base for the application of & \\  & & gold leaf), now detached. & & \\ \hline \multirow{6}{*}{SG\_44} & \multirow{6}{*}{Panel E} & Traces of a layer of preparation for the & \multirow{2}{*}{Understanding of the application technique} \\  & & prediction of gold leaf for the creation of & & \\  & & rays of the risen [PERSON]. The surface of the & & \\ \cline{1-1}  & & layer taken is raised and tenaciously adheres & \\ \cline{1-1}  & & to the plaster. Given the small number of & & \\ \cline{1-1}  & & traces still present, the sampling has been & & \\ \cline{1-1}  & & reduced to minimal quantities. & & \\ \hline \end{tabular}
\end{table} 
Table 1: Description of the samples collected for the identification of original binders and degraded superficial varnishes or coatings.