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Report from the lab: analysing stable isotopes in cod bones

Medieval Oslo gradually became part of an international trading network. Written sources indicate that export of cod, hides and furs played an important role in the trade. Interestingly, fish bones make up a relatively small part of the total remains of animal bones from medieval Oslo. Did the rising volume of fish export result in a declining availability of fish in Norwegian towns? Or were Arctic stockfish consistently available in Oslo? Alex Hirons is now analysing fish bones found in the excavation of Oslogate 6 by stable isotopes of carbon, nitrogen, Sulphur and hydrogen. We are trying to find out from where Oslo was securing its fish supply.

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Alex promise that there`s a smile behind the mask 

Photo: Alex Hirons

Here is Alex, reporting from the lab preparing Batch 2 for demineralisation:

I cleaned the samples with a sand blaster & weighed total cleaned sample.

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A queue for cleaning. Photo: A. Hirons

I then took a sub-sample with a Dremel drill, & placed this into a test tube (all labelled with sample code & weighed the week before).

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The Dremel drill for subsampling. Photo: A. Hirons

These tubes are then re-weighed once they contain the sub-sample, & the empty tube is subtracted to find the exact sample weight.

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Weighing a sample. Photo: A. Hirons

All samples then submerged in 0.5 molar Hydrochloric acid, covered with foil & put in the fridge. This is to remove the mineral component of the bone, leaving behind the collagen we need for isotopic analysis.

These samples are monitored daily; samples that are ready will be soft & malleable. This is checked using a glass pipette to see how rubbery the sample is (I.e., if you press it against the side of the test tube, does it mould itself to the tube or is it still hard/stiff?). The acid is replaced every other day; excess acid is poured or filtered away, & fresh acid is applied. Making new bottles of correctly-diluted acid is another regular lab job!

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Changing the acid for demineralising samples. Photo: A. Hirons

The samples are now demineralising (80 samples in total). The next step is gelatinisation. Wait and see!

By Alex Hirons/Marianne Vedeler
Published Dec. 21, 2020 9:59 AM - Last modified Feb. 11, 2021 10:54 AM

About Food in the Middle Ages

On this blog, we’ll talk about what kind of food people ate in the Norwegian Middle Ages by shining a light on local cultivation and recipes. We will show results from the research laboratories and exciting artifacts from our collections that tell of a diverse food culture, especially in the medieval towns, which consisted of so much more than just meat and porridge.