Effects of fires and biofractionation of carbon isotopes on results of radiocarbon dating of old textiles: The Shroud of Turin

A laboratory model especially created to ''reproduce'', i.e. to simulate the physical/chemical conditions of the 1532 Chambery fire was developed for the purpose of determining experimentally the probability that fire-induced chemical modifications of the Turin Shroud textile cellulose had occurred and evaluating its possible impact on the radiocarbon dating results. In these studies, both old Russian and old Middle Eastern (En Gedi, Israel, sc 100 AD 100) linen textile samples were tested by near-IR reflectance spectrophotometry, field ionization/field desorption mass spectrometry, and conventional AMS analysis. We found that the different fire-simulating model conditions were able to promote the carboxylation of unscreened OH-groups in textile cellulose molecules. This carboxylation process involves carbon-containing combustion gases, CO and CO2, in the presence of silver cations, water and heat. As a result, a significant additional amount of C-14 and C-13 atoms incorporate into the textile cellulose structure as a portion of carboxy-groups. Radiocarbon ages of experimental textile samples incubated under fire-simulating conditions have been estimated by the common AMS technique with correction for C-isotopes fractionation. As seen from the resulting data, fire-induced carboxylation, i.e. ''carbonization'' of the textile cellulose, Leads to a significant error in the radiocarbon dating results. The extent and mechanism of this phenomenon as well as the problem of accuracy and the limitations of the radiocarbon method are discussed. AII experimental data and theoretical statements presented in this work deal with the re-evaluation of the Shroud of Turin dating results obtained by Damon ct al, using a conventional radiocarbon approach. (C) 1996 Academic Press Limited