C 6.2. Glass-like layers

Areas of the parchment with an altered appearance resulting from localised degradation.
The physical condition of the parchment is directly impacted by the degradation of the collagen fibres (total or partial gelatinisation). The existence of glass-like areas is an indication of degradation. These are areas where structural and chemical changes also cause the visible transformation of the surface, by changing its relief and tonality. The transparency of the parchment also changes, by both decreasing or increasing. The presence of glass-like areas is, in turn, one of the main causes of document deformation. The presence of glass-like areas is a direct indication of a decrease in the physical strength and hydrothermal stability of the parchment. Glass-like areas are often the combined result of several causes.