We report here progress on our technique for 14C dating of pictographs. We use low-temperature oxygen plasmas coupled with high-vacuum technology to selectively remove carbon-containing material in the paints without contamination from inorganic carbon from rock substrates or accretions. Pictograph samples dated generally agree with the ages expected on the basis of archaeological inference. We also used the technique on eight samples of known 14C activity. In each case, our results agree with previously determined ages. Each of these determinations supports our conclusion that the technique has the potential of producing accurate and reliable ages. Four new 14C dates were obtained on a quartered Pecos River-style pictograph sample (41VV75-37A-D). We used an idealized model to estimate a lower limit for the age of the pictograph 41VV75-37. The “age” itself should not be taken seriously as a meaningful limit as the measured age indicates that background organic material in the basal rocks and accretions can be a serious problem.
This carbon dioxide would be converted to a graphite pellet and then the 14 C content would be measured by AMS. Because the plasma-oxidation process takes place at a temperature (∼200°C) below that at which carbonates decompose (∼800°C), there is no reason to remove the carbonates, thus bypassing the need to treat the sample with harsh acid (Chaffee et al. 1994; Russ et al. 1992 ). Because humic substances from the burial environment remain an issue, pretreatment to remove those is necessary, but that can be accomplished on proteinaceous textile fibers with less damage by use of a pH 8 phosphate buffer treatment rather than the standard sodium hydroxide treatment (Armitage and Hardemon 2010 ).