The use of organic binders in monumental terracruda sculpture: Integrating Sanskrit texts with spectroscopic and spectrometric data in the study of Tepe Narenj and Qol-e-tut examples (Kabul, Afghanistan, 5th to 11th centuries CE)

Abstract

This work is part of a broader research project aimed at understanding the technology of making Buddhist monumental terracruda (air-dried clay) sculptures and contributing to the design of specific recovery protocols and conservation treatments for archaeological examples. Previous studies have been mainly based on information obtained through the comparative study of traditional knowledge preserved in India and petrographic, mineralogical, chemical and botanical characterization performed on Afghan examples from Buddhist sites of Tepe Narenj and Qol-e-tut (5th to 11th centuries).

Here the focus is to verify the hypothesis of the addition of possible organic binding substances to elaborate the modelling pastes on the examples of Tepe Narenj and Qol-e-tut, with particular interest in the search for gums, as these compounds had been identified by analyses of other Afghan examples and their use is documented in India today for the finishing layers of the type of sculptures under study.

So far, the studies that have looked for organic binders have done so with the aim of analysing painting techniques. However, ancient sacred texts (8th - 17th centuries CE) mention a wide use of organic substances also in the preparation of clays. In a pioneering approach aimed at elucidating their presence in the modelling pastes, we used a staggered analytical approach as part of a European IPERIONHS project with first, FTIR analyses to verify their inclusion and if possible, their specific groups and secondly, GC–MS analyses to characterize them. Finally, we used a structural analytical approach based on MALDI-TOF mass spectrometry to study the polysaccharides and access their taxonomic information.

The results suggest that multiple organic binders were added, and the use of gums has been confirmed. Although this represents only a first step in the study of the use of organic binders in the modelling pastes and plasters of monumental terracruda sculpture, the results appear to be consistent with the complex processes described in ancient sacred literature related to their preparation.