## 3 Results and Discussion
### Analysis of Binding Media and Wood Specimens  
#### 3.2.1 Analysis of Paint Sample: Natural Plant Resins and Oils  
GC-MS analysis showed evidence of a drying oil only in one sample (H3a, Table 4); the C16/C18.0 value (1.5) obtained for the top two layers of H3a agrees with the values previously reported for linseed oil [38]. Drying oils have been identified at Uvdal and Rollag (ca. 1650s), however, when the oil was incorporated into the pictorial layer is unknown. The oil could have been from a previous conservation treatment or it could have been part of the original material [3]. During the 1600-1700s, linseed oil was accessible in larger Norwegian cities. However, for the artists at Heddal and Eidsborg, they would most likely need to transport all of their materials with them or have them delivered to the church site [1]. Therefore, it is more likely that these findings are suggestive of an area that was retouched by [PERSON] in the 1950s [6; 8]. As mentioned in Section 3.1.2, the specific materials used during this 20 th century restoration were unknown; however, based on prior experience of retouching done by [PERSON], it was assumed that a glue-based paint was used at Heddal. The findings presented here within suggest that retouching was also performed with oil. Furthermore, these findings support the results of [5], in which alkaline saponification analysis indicated the presence of oil in a Heddal sample.  
GC-MS analysis can also be used to examine the presence of glycerol in a paint sample, if an abundant amount of oil is present. However, this is complicated by the fact that glycerol can also be derived from egg yolk [47]. For the samples examined, glycerol was not detected (Figure S8, see Supplementary Material). Additionally, if a whole egg were used, the lipid content of the untreated sample (E2a) would have been greater than 0.01%.  
Unlike the GC results, absorption bands indicative of oil were only identified in Eidsborg samples (Table S14 in Supplementary Material). Here, the IR absorption peak located near 1735-1745 cm\({}^{-1}\) has been considered as discriminative for the presence of oil. However, as these IR results were not corroborated by the adopted chromatographic methods (Table 4), future studies will be conducted to clarify the use of drying oils at Eidsborg.  
Finally, GC results also showed contamination to the paint layers. Allantoin, a product of urine, was found in the ground layer of E3a (Figure 7), but not in the upper layers. The most probable explanation of its presence is that it was excreted from a housefly before the artist applied the motif. Additionally, GC-MS (Table 4 and Figure 8) and IR (Table S14, See Supplementary Material) analysis of samples from both churches showed the presence of wood itself, or wood-derived products (e.g., resin), strongly indicating that the wooden planks are contaminating the painted layers. Additionally, in some cases, the spectral features almost completely mask absorption bands related to other compounds (e.g., E2b, Table S13 in Supplementary Material). As this case study focuses on polychrome wooden structures, it is not surprising that the acquired results included peaks readily assigned to wood.