Mühlen Axelsson, K.; Larsen, R.; Sommer, D. V. P.; “Dimensional studies of
specific microscopic fibre structures in deteriorated parchment before and
during shrinkage”, Journal of Cultural
Heritage 13(2) (2012) 128–136
DOI:10.1016/j.culher.2011.08.001 (restricted access)
Abstract:
This paper reports the first systematic study of the
dimensions of morphological changed microscopic collagen fibres in historical
and new reference parchments with the aim to improve the knowledge on
deterioration and the diagnosis of their damage in connection with conservation
activities. The dimensions of fibres from the parchments were measured before
and during shrinkage, with special emphasis on fibres with degradation
characteristics designated as “pearls on a string” and “butterflies”. In
addition, measurements of the total shrinkage of the length of fibres and
pieces of parchment were also carried out. The observations support the
assumption that in vivo transformation of the fibre structure by natural ageing
is similar to that taking place when heating parchment and fibres in water.
Based on statistical cluster analysis, four subpopulations of pearls
representing different stages of deterioration are found. Moreover, the
dimensional changes in the specific structures observed at room temperature can
be related to specific temperatures in the interval of shrinkage suggesting
that the hydrothermal stability of the fibres may be predicted on the basis of
the ratio between length and width of the so-called pearls (Pl/Pw). The total
shrinkage measured is drastic, in average around 56% for fibres and 43 to 48%
for pieces of parchment depending on the direction of the skin. The total
shrinkage of fibres corresponds to a mean change in the ratio Pl/Pw from around
10 to around 2.3. Finally, relations between the measured dimensions at the microscopic
level with those of collagen at nanoscopic and molecular levels including known
and potential chemical splitting points strongly indicate that the formation of
the butterfly-like fragments formed by cleavage of two adjacent pearls in the
fibre can be ascribed to chemical modification of specific tripeptides in the
collagen molecule.