Atlas of Micromorphological Degradation of Archaeological Birch Bark

In this paper we present an atlas of micromorphological degradation of archaeological birch bark for the first time. We analysed the morphology of 13 samples extracted from ice-logged, waterlogged and cave-retrieved objects dated from the Neolithic to the Middle Age by means of light microscopy (LM) and transmission electron microscopy (TEM). We then compared their morphology to that of a contemporary sample, both intact and decayed. In all samples, 13 morphological characteristics that can be associated with fungal, bacterial, chemical, mechanical and light degradation are defined and described, and example LM and TEM images are provided. This novel atlas provides conservator-restorers a much-needed tool to relate the macroscopic appearance to the microscopic structure of birch bark objects. The most important macroscopic features allowing estimation of the state of preservation at the cell level are colour changes, loss of pliability, presence of delamination and increased brittleness. Colour change and delamination can be connected to microscopic features, and microscopic analysis can trace whether they were caused by biotic, chemical or physical decay. However, increased brittleness cannot be connected to a specific microscopic feature.

Automated summary

This paper presents an atlas of micromorphological degradation of archaeological birch bark, analyzing 13 samples extracted from various archaeological objects and comparing them to a contemporary sample. The study identifies 13 morphological characteristics associated with degradation and provides LM and TEM images. The atlas offers a useful tool for conservator-restorers to connect macroscopic appearance to microscopic structure, especially in relation to factors such as color changes, loss of pliability, presence of delamination, and increased brittleness.