Chemical analysis of cacao residues in archaeological ceramics from North America: considerations of contamination, sample size and systematic controls

Abstract We address the issue of contamination in sampling and storage procedures and the requirements of sample size and controls necessary to assay ceramic vessels for absorbed chemical residues. We focus our discussion on the detection and quantification of the three methylxanthines – caffeine, theobromine and theophylline as a means to infer whether Mississippian and Southwestern vessels had been used for the consumption of a stimulating drink made from the seeds of Theobroma cacao , a tree that grows in the Mesoamerican tropics. Our research detected two statistically differentiated concentration levels of methylxanthines on objects in museum storage: vessels with low levels of methylxanthines from airborne particulates that we attribute to environmental contamination, and vessels with significant higher levels of the methylxanthines that we attribute to the archaeological record reflecting prehistoric cacao consumption. We propose that cacao was imported into the American Midwest/Southeast during the Mississippian platform mound tradition AD 1000–1300 and into the American Southwest during the Chaco Great House tradition AD 900–1200 and the Hohokam platform mound tradition AD 1300–1400.