What was pottery used for?

Studying the vessel function and its contents are fundamental to understand the motivation of the adoption of pottery by people.

How is it done?

During a meal preparation, a part of the food will be absorbed within the porosity of the ceramic vessel. It can also form a “food crust”, a charred deposit that will adhere at the surface of the pot. The food contains organic molecules that are very stable, the lipids. When the condition are good, as protected within the ceramic, they can be preserved for thousands of year. So from a fragment of ceramic vessel discovered in an excavation or from what was left of a food crust, we can extract and analyse ancient biomolecules that will allow us to identify what was cooked in this pot.

Do you want to know more?

Archaeologists are using different techniques to extract the ancient lipids. Here is the one most frequently used in this project.

Application of correspondence analysis allows combination of these features and representing all interconnections among different ceramic assemblages.

• To extract the lipids from the pottery or food crust, we first reduce it to powder.
• Then we mix it with organic solvent (methanol) and acid (sulfuric acid) to dissolve the molecules and help them to be released from the mineral matrix. The reaction take several hours at 70°C.
• Now we add another solvent much less polar. As the lipids are closer in polarity to this solvent they will “migrate” in it. We pipette out this solvent and dry it.
• We have now a lipid extract that we can analyse.
• Gas chromatography - mass spectrometry (GC-MS). It allow us to separate and identify the various molecular compounds. We are notably interested by some molecules that are characteristic of specific food groups, it is what we call a “biomarker”.
• Gas chromatography - isotope ratio mass spectrometry (GC-c-IRMS). It allow us to obtain the stable isotopic value of the main compounds of the extract. The values are different between different group of foods. We can for example make the difference between marine and freshwater fishes.

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