Identification of cellulose nitrate based adhesive repairs in archaeological pottery of the University of Melbourne's Middle Eastern archaeological pottery collection using portable FTIR-ATR spectroscopy and PCA

Abstract

A previous study of the Cypriot pottery collection housed in the Ian Potter Museum of Art at the University of Melbourne found approximately two-thirds of adhesive repairs are primarily composed of cellulose nitrate (CN). This is of concern as CN has a limited lifespan (6-20 years), which has implications for the strategic management of the collection. To gain a greater understanding of the prevalence of CN based adhesive repairs in the archaeological context, the original FTIR-ATR spectroscopic survey was extended to incorporate the University's Middle Eastern archaeological pottery collection. Micro-samples were removed from artefacts using acetone swabs. Analysis of adhesive FTIR spectra identified CN to be present not only as the primary polymer in approximately one-tenth of repairs, but also as a secondary polymer in poly(vinyl acetate) (PVAc) and acrylic adhesive formulations, observed as a weak peak at ~1656 cm-1. CN's secondary presence in PVAc adhesive formulations is demonstrated using principal component analysis (PCA) and the diphenylamine spot test for CN. Re-analysis of adhesive IR spectra from the Cypriot pottery collection found CN to be present as a secondary polymer in this collection as well. It is concluded a combined methodology of collecting and identifying FTIR-ATR spectra of adhesive repairs from archaeological pottery collections followed by PCA analysis bring to light adhesive formulations which can inform the management of pottery collections.