MARVIN W. ROWE, Department of Chemistry, Texas A&M University, P. O. Box 30012, College Station, TX 77842-3012
 
 

After its introduction five decades ago, radiocarbon dating still remains 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 (Russ et al. 1990, Nature 348:710) will be presented. Low-temperature and low-pressure argon and oxygen plasmas, coupled with high vacuum technology, remove carbon containing material in pictograph paints without contamination from inorganic carbon in the rock substrates (CaCO₃) or mineral accretions (CaC₂O₄). The rock painting samples dated so far generally agree with ages expected on the basis of archaeological inference. The technique was used on 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 also measured. Chemical pretreatment with ~1 M NaOH with ultrasonication at 50ºC 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 so far support the conclusion that the plasma-chemical technique produces viable ages on rock paintings, without regard to the pigment used. However, the technique cannot be considered conclusive, but like all present techniques used to date rock art, must remain for the present at least provisional. So far, rock paintings have been dated from Angola, Arizona, Australia, Belize, Brazil, California, Colorado, France, Guatemala, Idaho, Mexico, Missouri, Montana, Russia, Texas, Utah, Wisconsin and Wyoming. New unpublished results will be discussed.