On the Beach: New Discoveries at Harlyn Bay, Cornwall

Introduction The porous nature of unglazed pottery vessels ensures that during the processing of food lipids become absorbed into the vessel wall. These lipids include remnant animal fats, plant oils and plant waxes, which are known to survive in archaeological deposits for several millenia (Evershed et al., 1999). The major compounds present are lipids, i.e. the fats, oils, waxes and resins of the natural world, recoverable by solvent extraction, which are then quantified and identified by high temperature-gas chromatography (HTGC), GC/mass spectrometry (GC/MS; Evershed et al., 1990) and GC-combustion-isotope ratio mass spectrometry (GC-C-IRMS; Evershed et al., 1994; Mottram et al., 1999). Characterisation of lipid extracts to commodity type rests on detailed knowledge of diagnostic compounds and their associated degradation products arising during vessel use or burial. For In archaeological pottery free fatty acids commonly dominate lipid extracts over compounds that are characteristic for fresh fats and oils (i.e. acylglycerol moities). Compound-specific stable carbon isotope determinations, using gas chromatography-combustion-isotope ratio mass spectrometry (GCC-IRMS), allows the carbon stable isotope (δC) values of individual compounds to be determined, providing an important complementary criterion for classifying the origins of lipids. δC values of the principal fatty acids (C16:0 and C18:0) present in degraded animals fats are effective in distinguishing between different animal fats, e.g. ruminant and non-ruminant adipose fats and dairy fats (Evershed et al., 1997a, Dudd and Evershed, 1998), as well as in the identification of the mixing of commodities (Evershed et al., 1999, Copley et al., 2001).