# Atlas of Micromorphological Degradation of Archaeological Birch Bark
## 2 Materials and Methods
### Samples  
The reference bark was a mature birch phelem collected from a felled _Betula pendula_ tree about 30 years old in the district of Vex (Valais, Switzerland) in November 2014 (Figure 2). The naturally decayed bark was harvested from a fallen tree about 15 years old in Borgne Valley, Valais (Figure 3). The trunk was weathered in nature, laying on a sandy subsoil with stones. The fragment was chosen for its pronounced biological degradation, visible macroscopically as green, grey and brown-black staining, deposits and cracks. Such degradation was present especially at the lenticels and the inner bark (Figure 3). The ice-logged samples were taken from the Neolithic bow case from the Schnidejoch ice patch, Switzerland (Figure 4), and from three birch bark fragments retrieved from the Lendbreen ice patch, Norway (Figure 5). The Schnidejoch bow case has been described in a number of publications [63; 64; 65]. This object is dated to around 2800 BC and consists of three parts, a lid and an upper and lower body, that were found under different circumstances and in different conditions. Each part is made of 2 to 3 layers of superimposed outer birch bark strips sewn together with lime best. The lid was subjected to a harmful ethanol treatment that extracted most of the alcohol-soluble components from the bark. It is now stored dry at ambient temperature. The upper and lower body are both untreated and stored damp and frozen at -26 \({}^{\circ}\)C. The three Lendbreen birch bark fragments were found in a retreating ice patch located at the northern slope of Lomseggen ridge, Oppland (Norway). The ice patch extends from 1690 to 1920 m a.s.l. and the finds are dated between 300 and 1500 AD, with an accumulation of finds around 1000 AD [66]. The waterlogged sample was extracted from a Neolithic birch bark retrieved in Lake Moossee in Switzerland (521 m a.s.l) during an excavation in 2011 (Figure 6). The layer from which the bark was retrieved dates between 4500 and 3800 BC. Since excavation, this bark, which was originally not harvested but detached naturally from a tree, as the phloem is still attached to the bark, is stored in distilled water at 4 \({}^{\circ}\)C. The last fragment (Figure 7) was recovered from a cave named Kosackenberg, in the Kyffhauser mountains west of Bad Frankenhausen in Germany and excavated in the 1950s. It is dated to the Bronze Age (23001800 BC) and, after unburial, has been preserved untreated in a sealed container. Figure 3: Birch bark fragment harvested from fallen trunk degraded in nature. Outer surface, especially when in contact with the ground, shows green, grey and brown discoloration and vertical cracks. Lenticels have cracks and overlays and are areas no longer clearly defined. On the inner side, remains of brittle and brown-black stained phloem are present and black circular deposits indicate areas of increased degradation. Location of analysed sample 0 is indicated with red rectangle. Figure 2: Reference sample (**left**) was extracted from contemporary outer birch bark harvested from a mature tree with strong and pliable phelem (**right**). Sample has white powdery surface due to betulin content and slight delamination is present at the lenticel. Thick- and thin-walled cell bands are recognizable macroscopically as red and white bands, respectively, along the radial section. Figure 4: (**a**) Lower and (**b**) upper part of Schnidejoch bow case body, ground-facing side; (**d**) upper part, upward facing. Samples were taken from outer bark strips (1, 6, 7), middle bark strips (2) and inner lining (3, 4, 8). Outer and middle bark strips of bow case body have outer bark surface oriented towards inside, and inner lining has outer bark surface oriented towards outside. Sample 4 was extracted from a fragment probably from (**c**) lid inner lining. Sample 5 was a loose fragment found close to the lower part (not shown). Figure 5: **Left**: Lendbreen fragments; **right**: analysed samples. Sample 9 was taken from a weathered fragment; lenticels were fully eroded but sample was not brittle.