Featured image: a soil sample after being processed into a thin section and analysed through a digital microscope.
Volunteers from Suffolk Mind visited the McDonald Institute for Archaeological Research at University of Cambridge to find out more about how archaeological samples are processed there, as part of our community archaeology project Rendlesham Revealed.
A geoarchaeology survey was carried out at Rendlesham in July 2021, where 71 soil samples were extracted from an area in the valley by the River Deben. Additional soil samples were also taken from some of the archaeological features during the excavations at Rendlesham in September 2021. The aim was to understand the soil sequence, which may tell us more about the development of vegetation and the impact of human activity.
So what happens to soil samples after they have been collected in the field?
In November, we were joined by volunteers from Suffolk Mind to visit Professor Charly French and Dr Tonko Rajkovaca at the McDonald Institute for Archaeological Research, University of Cambridge to find out more.
We began the visit in the processing lab to learn how the soil samples are prepared.
When soil samples are brought back to the lab, they are air dried for at least 2-4 weeks and then oven dried, unless the soils are from wet deposits. The samples are then impregnated with polyester resin in a vacuum chamber. These are then cold-cured and then heat-cured to set the resin; this takes about a month or so.
Once they are set the soil blocks can be cut into “thin sections”. This is a long and technical process to ensure the sections are cut to the accurate measurements. The blocks are cut using a diamond-edge saw and then ground using a French Brot multi-plate grinding machine and polished several times until a thin section is produced.
We then were shown another lab, where the thin sections are analysed with a variety of polarised microscopes. The volunteers had a look at some of the prepared samples to see the detail of the soil structures and layers.
But the work doesn’t stop there. Some of the samples are also sent to specialists at other laboratories to be analysed for pollen and microscopic organisms, as well as radiocarbon dating.
This event was undertaken as part of the community archaeology project Rendlesham Revealed: Anglo-Saxon Life in South-East Suffolk, funded by the National Lottery Heritage Fund.
If you want to get involved with the Rendlesham Revealed project and future fieldwork, you can sign up to our e-newsletter for updates.
Find out More:
Watch this video by Professor Charles French for a tour of the lab and to find out about how “thin section” soil samples are made