Archaeometry 50, 1 (2008) 101–113 doi: 10.1111/j.1475-4754.2007.00368.x *Received 11 August 2005; accepted 20 December 2006 †Corresponding author: email R.P.Evershed@bristol.ac.uk © University of Oxford, 2008 Blackwell Publishing Ltd Oxford, UK ARCH Archaeometry 0003-813X © University of Oxford, 2008 XXX ORIGINAL ARTICLES Experimental evidence for the processing of marine animal products R. P. Evershedet al. *Received 11 August 2005; accepted 20 December 2006 EXPERIMENTAL EVIDENCE FOR THE PROCESSING OF MARINE ANIMAL PRODUCTS AND OTHER COMMODITIES CONTAINING POLYUNSATURATED FATTY ACIDS IN POTTERY VESSELS* R. P. EVERSHED, 1 † M. S. COPLEY, 1 L. DICKSON 1 and F. A. HANSEL 2 1 Organic Geochemistry Unit, Bristol Biogeochemistry Research Centre, School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK 2 Departamento de Química, Univesidade Federal de Santa Catarina, 88040 900, Florianópolis, Santa Catarina, Brazil ω-(o-Alkylphenyl)alkanoic acids are known to form in vitro from triunsaturated fatty acids following protracted heating. These compounds have recently been identified in absorbed lipid extracts obtained from archaeological pottery vessels, providing a potentially valuable new class of indicator for the processing of commodities, such as marine oils, which contain high abundances of polyunsaturated fatty acids. Experiments were conducted to assess whether ω-(o-alkylphenyl)alkanoic acids form when pure compounds and complex triacylglycerol mixtures are heated with a fired clay. The results demonstrate that ω-(o- alkylphenyl)alkanoic acids are only produced following heating of unsaturated fatty acids (tri-, di- and monounsaturated species) or complex unsaturated fatty acyl lipids at around 270°C. Heating saturated fatty acyl lipids does not yield ω-(o-alkylphenyl)alkanoic acids. Thus, when searching for evidence for the processing of marine derived animal fats in archaeological pottery vessels, it is essential that: ω-(o-alkylphenyl)alkanoic acids of carbon length C 18 and C 20 should be present, ideally with C 22 also detectable (if only in trace abundances), together with at least one of the three isoprenoid fatty acids (phytanic, pristanic or 4,8,12-tetramethyltridecanoic acid). KEYWORDS: MARINE ANIMAL PRODUCTS, ORGANIC RESIDUE ANALYSIS, ω-(O-ALKYLPHENYL)ALKANOIC ACIDS, ISOPRENOID FATTY ACIDS, δ 13 C VALUES INTRODUCTION Fatty acids, mono-, di- and triacylglycerols arising from the processing of food (e.g., cooking) in unglazed pottery vessels are the most commonly encountered class of organic compounds in visible and absorbed organic residues in potsherds. Research performed over the past two decades has greatly increased the understanding of the factors affecting the preservation and degradation of fatty acyl lipids and provided robust means of identifying their origins (for reviews see Evershed 1993; Evershed et al. 1999, 2001, 2002). Thus, it has been possible to detect the processing of a wide range of commodities, including: ruminant and non-ruminant carcass and ruminant dairy products (e.g., Evershed et al. 1997, 2002; Dudd and Evershed 1998; Copley et al. 2003, 2005a,b,c,d) and specific plant oils (Passi et al. 1981; Copley et al. 2001, 2005e). Degradative reactions have been recognized including those associated with vessel use and