Isotope Analysis | History Visits

Isotope and Lipid Analysis of Residue on Pot Sherds

This is a really fascinating aspect of science applied to archaeology. Basically, they can grind down pot sherds into powder and then analyse that powder to determine what chemicals are in it. The chemicals they can identify can show what things were stored and/or cooked in the pot.

Amazing, right!

And they can apply this science to other materials too.

This study at Eye in Suffolk analysed flints found in a pit to see what the possible purpose of the arrangement might have been. On several settlement sites there are found pits dug which have charcoal in the bottom in a lattice like pattern which are covered with flints. The flints had lipids from ruminants on them, which basically means the either cattle, sheep or goat had been in contact with them. The suggestion put forward in the report is that the pit may have been some type of oven, with wood burning at the bottom, meat placed inside and then covered with flints, which would heat up and then maintain the heat for the cooking time.

This study at Flixborough, Lincolnshire showed that "Ruminant products (meat and/or dairy) appear to be the most frequently processed animal resource in ceramic containers at Flixborough, followed by dairy products and then omnivorous animals, including chickens, which show some similarities with the relative abundance of faunal remains". Flixborough is a high status site dating to the mid 8th to early 9thc.

A multi-period site at West Cotton, Raunds, Northamptonshire (late Saxon to 1500) reported - "The two main pottery forms found at the site were highly specialised, with bowls (or cantels) likely being used as measures in grain processing while jars were mainly employed for cooking stews and potages consisting of sheep or cattle carcass meats and, occasionally, leafy vegetables such as cabbages and leeks. The jugs and pitchers did not contain any lipid suggesting they were used solely for holding water or some other aqueous liquid and less commonly used vessels also appear to have had specialised uses, including spouted bowls, likely employed to render fat or clarify butter and an inturned-rim bowl, used for the mixing of tallow and beeswax, possibly for use as an illuminant, sealant or lubricant." Purchase the full article here.

I took the following notes from a report on "absorbed lipid residues from twenty-four 6th to 9th century coarseware potsherds from the major Anglo-Saxon trading centre of Hamwic (Southampton, UK)":

jars with soot; cattle predominant with sheep increasing; marine resources mussel oyster and fish bones; fish such as carp and catfish; sea foods such as limpets, shrimps, cuttlefish, crabs and sponges; beeswax may have been applied as a water-proofer or honey stored in the vessel; cabbage leaves and a fat source; ruminant fats
it was found that 5 vessels were exclusively used for processing an animal fat, 2 vessels for preparing cabbage and 7 vessels for the preparation of both foodstuffs; positive evidence was found for the preparation of cabbage
"the vessels were associated with the consumption of meat, fish, vegetables or a mixture of multiple foods"
"the presence of many degraded lipids which are only formed upon exposure to high temperatures(e.g. mid-chain ketones, w-(o-alkylphenyl) alkanoic acids) are consistent with the sooty deposits on all sherds, confirming that the pots were used as cooking vessels."
"These results suggest that meat was cooked and consumed alongside vegetables in dishes such as stews."
"The lipid biomarkers therefore provide direct evidence of stewing, the dominant cooking method in the Anglo-Saxon period based upon historical sources."
"Historical sources suggest that salt fish would have been boiled, possibly in milk or butter (Hagen 2006). For the first time, this analysis has potentially demonstrated this archaeologically, through the co-occurrence of ruminant and marine fats in the same vessel."
Vessels entered Hamwih as containers and were then reused for as cooking pots.
"Marine products which are heated to temperatures over 270 °C also have a characteristic signature owing to the catalytic conversion of (C16 –C22) (poly)unsaturated fatty acids to w-(o-alkylphenyl) alkanoic acids upon heating in ceramic vessels (Craig et al. 2007; Evershed et al.2008; Hansel et al. 2004; Heron et al. 2010)."

Baeten, J., Jervis, B., De Vos, D. and Waelkens, M. 2013, ‘Molecular evidence for the mixing of meat, fish and vegetables in Anglo-Saxon courseware from Hamwic, UK’, Archaeometry 55(6), 1150-74.

Read the full report here.