Sulphur distribution in parchment and leather exposed to sulphur dioxide

Scanning electron microscopy, with x-ray capture, showed layered distributions of sulphur in parchment cross sections. In artificially aged parchments (exposed to SO2 at 25 ppm) sulphur accumulated in layers that were less dense (i.e. showing low electron backscatter). Historical parchments showed layered distributions of sulphur, some of which was deep in the parchment profile. Surprisingly, calcium appeared not to be associated with sulphur in artificially aged samples. However in degraded historical leathers and parchments there was often a close association between sulphur, calcium, iron and copper. These metals may well increase the rate of collagen degradation by catalyzing the formation of sulphuric acid.