Towards a description of the degradation of archaeological birch bark.

Archaeological birch-bark artefacts from ice patches are rare and little knowledge about their conservation exists. The degradation mechanisms are unknown and it is uncertain how they affect the mechanical properties and the cell structure. Due to this lack of knowledge, the treatments for archaeological birch-bark artefacts usually mimic those for waterlogged wood, which are tuned to the preservation condition of the object. This is assessed by measuring the maximum water content and, in some cases, the basic density and by microscopic examination of microscopic examination. In this paper, it is explored whetherthese parameters and techniques can be used to characterise the degradation of archaeological birch bark. Light microscopy examinations showed that cell wall deformations and fractures were present in both unaged reference material and archaeological birch bark and are not a distinct attribute of degradation. Cell collapse was not detected in ice-logged samples, while loss of birefringence is a potential tool to characterise degradation. Birch bark cells cannot be saturated with water, not even in the case of waterlogged archaeological samples. The authors conclude that maximum water content is not a diagnostic tool to quantify degradation