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
whether these 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.