Resin and lac adhesives in Southwest archaeology and microchemical tests for their identification

Christina Bisulca, Marilen Pool, and Nancy Odegaard

Abstract

The peoples of the Southwest used a variety of organic adhesives including pine resin and insect lac (shellac). A survey at the Arizona State Museum characterized over 100 artifacts with resinous materials or residues using Fourier transform infrared spectroscopy. Less expensive and more accessible methods—UV-induced visible fluorescence and microchemical testing—were also used for characterization and their accuracy was compared to Fourier transform infrared spectroscopy results. For pine resin, the Raspail test was used; for insect lac, a new microchemical test was developed based on the pH sensitivity of anthraquinone dyes present in insect lac exudates. Results show that microchemical tests are generally reliable even with archaeological materials. This is important as archaeological artifacts are aged and adhesives are often contaminated with burial accretions. By systematically evaluating these tests, further insights were gained. Most importantly, the Raspail test was found to indicate any terpenoid exudate and is not specific to pine resin. These results show that although microchemical tests continue to be useful, care should be taken when interpreting results.

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