Abstract
A range of pretreatment methods was applied to 6 known-age historical parchments to investigate the most suitable methods for effectively removing contamination and ensuring accurate radiocarbon dates while minimizing unnecessary destruction of potentially valuable historical documents. The methods tested included an acid wash, different concentrations of acid-base-acid (ABA) pretreatments, the current routine ABA method applied at the Oxford Radiocarbon Accelerator Unit (ORAU) that includes an additional bleach treatment, and extraction of collagen. The C:N atomic weight ratio of the untreated and pretreated parchment fractions was observed to be a useful indicator of the presence or successful removal of contaminants. The pretreatment methods that produced the most accurate 14C dates and acceptable C:N ratios were found to be ABA protocols (without bleach) and collagen extraction; solvent washes and acid pretreatments alone were not sufficient to remove all contaminants and produce reliable 14C dates. The inclusion of a base wash did not affect the 14C dates of the samples, but did favorably influence the C:N ratio of the final product.
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