Material properties and durability of 19th-20th century Tibetan manuscripts

Most currently available research into Tibetan paper focuses on the earliest books from an archaeological perspective. On the other hand, scientific studies of the 19th-20th century Tibetan paper are largely missing, specifically with respect to material properties and paper permanence. To explore these, both conventional and modified methods were applied using reference historic material collection. Material properties such as fibre morphology, paper pH, degree of polymerisation (DP), water and ash contents were investigated. The measurement methods for starch and protein content were explored-and we report on a quantification method for the determination of starch content in paper. The degradation behaviour of Tibetan paper was studied using accelerated degradation experiments at two sets of conditions (80 C, 65% RH and 60 C, 80% RH) for up to 84 days in order to explore the applicability of existing dose-response functions. The results demonstrate that examined 19th-20th century papers used in Tibetan books, were prepared using diverse fibres, similar to traditional Chinese paper. Most of paper sheets presented laminated structures, where starch was used as the predominant glue. The layers within one paper sheet are identical, as evidenced by similar pH and DP values among layers in one sheet. The studied collection of papers tends to have similar properties to modern Chinese paper since most of both types of papers present pH 6.5-8 and DP 1000-2000. The accelerated degradation experiment shows that papers used as writing support in Tibetan books follows the same principle of degradation as western paper has demonstrated, i.e., the rate constants of degradation depend on paper pH, temperature, and relative humidity of the environment. This research expands our understanding of this collection and inform preventive conservation of modern Tibetan manuscripts.