Dating Pictographs with Radiocarbon

Dating Pictographs with Radiocarbon


We report here progress on our technique for C-14 dating pictographs. We use low-temperature oxygen plasmas coupled with high-vacuum techniques to selectively remove carbon-containing material in the paints without contamination from rock substrates or accretions. We dated >16 pictograph samples that generally agree with the ages expected on the basis of archaeological inference. We have shown that carbonate and calcium oxalate decomposition does not occur during our procedure; little mass fractionation is produced. We also used the technique on samples of known C-14 activity. in each case our results agreed with previously determined ages of archaeological charcoal samples. Two samples of the standard Third International Radiocarbon Intercomparison wood yielded ages in near accord with the accepted value. We used C-14-free samples to establish that the method and apparatus do not have a significant live carbon background. Each of these determinations supports our conclusion that the technique has the potential of producing accurate and reliable ages. However, background organic material in the basal rocks and accretions can be troublesome, often completely negating the dates obtained.

For red and green paints, the pigments are invariably mineral based; however, in order to produce paint, it is necessary to suspend the mineral particles in a liquid medium (vehicle) that also serves to bind pigments to the substrate (binder). It is generally hypothesized that carbonaceous substances such as seed oils, plant resins, vegetable gums, animal fats, or beeswax were added to create a liquid paint mixture, thereby providing a source of organic carbon for radiocarbon dating (Ilger et al. 1995; Magaloni 1998; Morwood et al. 2010; Russ et al. 1990; Wright 2008Wright, 2010. Here we employed a low-temperature oxygen plasma system to isolate carbonaceous carbon used in the original paint mixtures from carbon-rich minerals in the substrate and natural rock coatings, allowing for direct radiocarbon dating of the artifacts (Rowe 2009).


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