A versatile integrated protocol to extract organic balms from archaeological linen: A new way to provide reliable radiocarbon dating for contaminated textile

Abstract

Radiocarbon dating of archaeological textiles can be particularly challenging when exogenous organic balms were deposited on their surface, as these organic mixtures can sometimes contain radiocarbon-depleted materials such as fossil bitumen. This is a key issue for radiocarbon dating of linen fragments used in the wrapping of Egyptian mummies, as bitumen has been repeatedly identified in several contexts. Radiocarbon dating of contaminated fragments can be facilitated by an analytical approach involving textile surface analysis by ATR-IR (Attenuated Total Reflection – Infrared Spectroscopy) to diagnose the state of contamination observed on each fragment, followed by a three-step organic extraction to remove all chemical families identified. This study was organized in two parts. First, mock-up samples were prepared, made of modern linen and experimental balms, to develop an integrated methodology based first on ATR-IR diagnosis for the state of contamination of textile, then on a solvent extraction to remove organic contaminants. The solvent extraction was monitored by ATR-IR and radiocarbon dating to control the complete removal of fossil compounds. The extraction protocol chosen is a three-step procedure (3x CHCl₃, then 3x hexane, then 3x MeOH), which can be tunable depending on the state and the nature of organic contamination on the textile. This new integrated methodology, which can be used in a versatile way to ensure reliable radiocarbon dating of linen archaeological textiles, was then applied to samples collected from an Egyptian child mummy conserved in Musée des Confluences, embalmed using a process that included the use of fossil bitumen. Thanks to this new protocol, we were able to date this mummy to the Late Period of Egypt.