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In this week's post, Akshyeta tells us about her recent sampling trip where she was collecting pottery samples for lipid residue analysis.
New ways of looking for food in old pots
Hello – Akshyeta here. My PhD research is studying absorbed lipid residues preserved in ceramic vessels from Indus settlements in northwest India and Pakistan. I am focusing on extracting lipids from vessels found in six Indus sites with occupation dating to the Mature Harappan (c. 2600-1900 B.C) and Late Harappan (c. 1900-1500 B.C) periods. I will then analyse these lipids using spectrometric and isotopic techniques (GC, GC-MS, GC-C-IRMS) to characterise what was being cooked and stored in specific categories of Indus vessels, and how the foods might differ between sites and across time.
I recently went to India to sample pottery that I will analyse as part of my thesis. I spent three weeks selecting and collecting ceramic powder from vessels from three sites located in northwest India. These sites had been excavated previously by the team of the Land, Water and Settlement project, the fore-runner of TwoRains.I spent four days in Varanasi, where I was graciously hosted by the team in the Department of Ancient Indian History, Culture and Archaeology at Benaras Hindu University (BHU) where I spent time sorting through the pottery and selecting the samples appropriate for my research. Apart from going through bags of beautiful, dusty Indus pottery all day, running on endless chai and samosas, I had a chance to visit the infamous Assi ghat and witness the evening prayers on the night of a full moon.
Studies have demonstrated that lipids are best preserved in cooking pots at the rim of the vessel, so I am targeting the rimsherds of cooking pots and storage vessels. I am also interested in sampling perforated vessels, as their distinctive shape may be linked to the processing of particular foods. Once I selected the potsherds I wanted, I packed them and took them to New Delhi, where I began the protocol for drilling and collecting powder from them.
Drilling pottery requires concentration and care – it is essential that samples are not contaminated from lipids that may be on fingertips or hands, and it is vital to prevent cross-contamination between samples. It is also important to wear a face and eye mask – inhaling clouds of dust from thousand-year-old pots isn’t very good for you! So armed with neoprene gloves, a fitted face-mask, eye mask and lab coat, I drilled and powdered nearly 90 potsherds, taking about 2-3 grams of powdered pottery from every selected sherd. It is important to follow established protocol by changing drill bits after removing the exterior surface of every sherd before drilling the interior portion, and of course, changing drill bits after every sample is drilled. The bits must be cleaned thoroughly with dichloromethane, a solvent that removes lipids from the drill bits.
I took care not to damage the exterior surface of the sherds and take pictures before beginning the drilling process. As this is essentially a destructive technique, it is extremely important to document and record aspects of potsherds before damaging them, so that others may be able to study them in the future.I have now brought these powdered ceramic samples back to the U.K, and will start to extract lipids from them in May in the laboratories of the British Museum. I will then analyse them via GC and GC-MS in order to characterise and identify the extracted lipids. The potsherds have been carefully labelled and wrapped in aluminium (which is lipid-free) and left in India, where they belong.
These powdered bits of pots have the potential to reveal direct evidence for what was being cooked up in settlements of the Indus Civilisation!