Documenting contamination in ancient starch laboratories

Ancient starch analysis is an important methodology for researching ancient ecology, plant use, diet, and tool function; particularly in the deep past when other proxies may not survive. Establishing the authenticity of ancient starch is therefore a major concern for researchers. Despite decades of archaeological application, there are currently no empirically-tested procedures for systematically assessing and reducing intra-laboratory contamination. At the Universities of Oxford and Calgary, we have tested laboratory consumables, airborne contaminants, and decontamination techniques (oxidisation, boiling, autoclaving, torching) to establish contamination sources, types and quantities, as well as the most effective methods of destroying them. In our laboratories, we found that (i) contaminant starches represent a restricted range of types, (ii) many commonly used consumables including non-powdered gloves and Calgon are starch-rich, (iii) passive slide traps often used to test for airborne contaminants generate unreliable proxies and unacceptably low statistical confidence, and (iv) decontamination procedures using weak acids and bleach are largely ineffective. This collaborative study has allowed us to identify and reduce the risk of contamination and to develop better internal authenticity criteria for future ancient starch studies conducted in our laboratories.