T02_05

Experimental Observations on Processing Leather, Skin and Parchment for Radiocarbon Dating

Davis M¹, Culleton B¹,   Rosencrance R², Jazwa C²

¹PSUAMS Radiocarbon Lab, Pennsylvania State University, University Park, United States, ²Department of Anthropology, University of Nevada, Reno, Reno, United States

Leather, skin, and parchment in archaeological, historic and museum settings are among the most challenging materials to radiocarbon date in terms of removing exogenous carbon sources -- comparable to bone collagen in many respects but with much less empirical study to guide pretreatment approaches. In the case of leather, the radiocarbon content of materials used in manufacturing the leather can vary greatly, their initial presence before pretreatment and absence afterward is difficult to demonstrate, and the accuracy of dates depends upon isolating the original animal proteins and removing exogenous carbon. Parchments differ in production technique from leather, but offer similar unknowns, and it is not clear that lessons learned in the treatment of one are always salient for treating the other.

We measured the radiocarbon content of variously pretreated leather, parchment, skin samples, and extracts, producing apparent ages that varied by hundreds or occasionally thousands of years depending upon sample pretreatment. We learned that physical precleaning and solvent washes were essential, bleach washes systematically destroyed samples, and pretreating leather, skin or parchment with ABA resulted in contaminated samples with low yields. A Longin style bone demineralization and gelatinization followed by XAD purification of the hydrolyzed amino acids most consistently resulted in radiocarbon ratios that were statistically indistinguishable from known ages of the samples. Fourier Transform Infrared Spectroscopy (FT IR) provided insight into the chemical composition of carbon reservoirs contributing to age differences between different pretreatments of the same sample, and mass mixing models were used to quantify various carbon reservoirs.