A similar procedure was used for the deer sample, except that no acid wash was performed. Previous results from our laboratory (Hyman and Rowe 1997; Pace et al. 2000) have shown that the acid washes are unnecessary with the plasma Radiocarbon Age of a Wisconsin Rock Painting ill chemical extraction since the plasma does not extract carbonate and Oxalate carbon. The deer sample was washed/sonicated three times in ~1 M NaOH for about an hour until the liquid appeared clear, and then washed/sonicated in doubly distilled, deionized water once to remove the NaOH.
The plasma-chemical extraction method introduced over a decade ago (Russ et al. 1990) and used here to extract organic carbon from the two Arnold/Tainter Cave rock paintings, has been described in detail elsewhere (e.g., see Hyman and Rowe 1997; Pace et al. 2000; and TAMU references therein). Thus, we discuss it here only briefly.
A rock art dating intercomparison program based on samples from the Upper Paleolithic site of Chauvet-Pont d’Arc Cave is highly desirable (Quiles et al. 2014). In addition, Pace et al. (2000) and Armitage (1998) demonstrated that base-treated plasma oxidation ages statistically overlap with ABA combustion ages.