Rock Art Research

After its introduction over five decades ago, radiocarbon dating is still the primary means for providing archaeological chronology. A review of the plasma-chemical extraction technique that permits direct AMS 14C dating of ancient rock paintings is presented. Low-temperature and low-pressure argon and oxygen plasmas, coupled with high vacuum, remove carbon-containing material in pictogram paints without contamination from inorganic carbon in the rock substrates (CaCO3) or mineral accretions (CaC2O4.nH2O). The pictogram samples dated so far generally conform to age ranges expected on the basis of archaeological inference. This technique was also used on standard materials of known 14C activity; results agreed within statistical uncertainty with previously determined ages. To establish that the method and apparatus do not have a significant live carbon background, 14C-free samples were measured as well. Chemical pre-treatment with ~1 M NaOH and ultra sonication at 50°C to remove possible contaminants is routine; HCl treatment normally used in dating archaeological charcoal to dissolve limestone is unnecessary with our approach. Almost all the radiocarbon determinations from our laboratory so far support the conclusion that the plasma-chemical technique produces viable ages for rock paintings, regardless of the pigment used. However, the technique must remain provisional until confirmed by another independent means. So far, we have dated rock paintings from Angola, Arizona, Australia, Belize, Brazil, California, Colorado, France, Guatemala, Idaho, Mexico, Missouri, Montana, Russia, Texas, Utah, Wisconsin and Wyoming. New results are presented.