## 3 Results and Discussion
### Pigment Analysis
#### 3.1.2 Mineralogical and Chemical Compositions of the White Basecoat  
Analysis performed using XRD, ESEM-EDS, and FT-IR support the findings of [PERSON] and [PERSON] [3; 5] and confirm the pigment assumption cited in the conservation reports [6; 7], that the basecoat is calcium carbonate-based (chalk). ESEM-BSE images (Figure S3, see Supplementary Material) either displayed a non-uniform porous matrix with micro-fossils (bioclasts) or fine particles distributed throughout the ground layer. The EDS results mainly consist of Ca which can be attributed to calcite from chalk, with minor concentrations of Al, Si, Mg, Pb, and Na probably deriving from impurities (Table S6, see Supplementary Material) besides C, O, and N.  
Figure 5 displays the typical FT-IR absorption bands for the historic paint, whereas the attribution to vibrational modes is compiled in Supplementary Material (Table S12). FT-IR spectra of all ground layers (see Supplementary Material) show the presence of high amounts of calcite, coupled with low quantities of silicates probably in the form of clay minerals. In many of the analyzed samples, a broadening of the main carbonate band (\(\upsilon_{3}-\text{CO}_{3}\)\({}^{2-}\) asymmetric stretching mode) has been observed coupled with slightly pronounced shoulders. This could be interpreted as being due to small amounts of dolomite (CaMg(CO\({}_{3}\))2), even if modifications in the positions of the \(\upsilon_{4}\) and \(\upsilon_{2}\) peaks were not observed. It is known that the main carbonate band can be split into three sub-bands due to the distortion of the carbonate group, which is suggestive of an amorphous state. The \(\upsilon_{3}\) position is mainly ruled by the stretching force constant of the C-O bond with the lower wavenumbers being related to amorphous forms, while higher values are generally related to crystalline forms [40]. The simultaneous presence of several organic and inorganic phases (see following subsections) is responsible for the complexity of the spectra, resulting from overlapping features. Consequently, XRD patterns were collected to clarify the nature of the crystalline phases in the mixtures. XRD analysis (Figure 6a,b) corroborates the SEM and IR findings, that calcite, with inclusion of other phases, is the main material used for the white basecoats. In Eidsborg (Figure 6a) small amounts of hydrocalcite (CaCO\({}_{3}\)\(\cdot\)H\({}_{2}\)O) were found in E3a, being the only consolidated sample in poor condition. Hydrocalcite has been found in natural deposits, as well as on frescos painted in a Portuguese semi-underground leisure room [41]. The presence of such a mineral is indicative of ongoing dissolution-recrystallization processes [41; 42]. Furthermore, water damage has been observed on the southern have wall of Eidsborg (e.g., tide lines) [7]. When examining samples taken from Heddal, the semi-quantitative analysis of XRD patterns shows relevant amounts of weddellite, a calcium oxalate di-hydrate mineral (CaC\({}_{2}\)O\({}_{4}\).2H\({}_{2}\)O) (Figure 6b). In particular, a consolidated sample in good condition (H1c) and unconsolidated sample (H2b) showed the largest amount of weddellite. Typically, the presence of this mineral phase is attributed to bacterial activity or a possible degradation process from past conservation treatments [43]. However, its presence in the unconsolidated sample (H2b) suggests that the sturgeon glue consolidant has little to no connection with this alteration. Moreover, the presence of weddellite can be used as an index, showing the degradation state of the pictorial image (Figure 3a and Figure S7 in Supplementary Material). Lastly, the presence of kaolinite was only detected in H3a, the only consolidated sample from Heddal that was in poor conservation condition. These kaolinite features are possibly due to the interaction between the X-ray beam and the subsequent orange layer (Table 2), or it could signify a retouching. Retouching in Heddal was known to have occurred during the 1950s, especially in areas of red and white paint.