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Excavating and conserving an Iron Age cauldron
In November 2004, a metal detector user discovered 12 cauldrons dating back to the Iron Age (around 800 BC – around AD 43), buried in a pit near the village of Chiseldon in Wiltshire, England. This chance find was carefully excavated by professional archaeologists and conservators from the British Museum.
Excavating the objects was very difficult because the weight of the overlying soil had crushed the very thin copper alloy (less than 1mm), flattening and distorting some of the vessels, causing collapse and physical interlocking between them. Despite appearing to be complete, the objects were very weak and cracked.
Removing complex archaeological deposits and fragile objects like these is done by lifting the object in a block of soil or, in the case of the vessels, in a collar lift. This involves clearing surrounding soil, but leaving the contents unexcavated and supporting with plaster of paris bandages. The objects are disturbed as little as possible so that they can be excavated fully in the controlled environment of the laboratory, and no evidence is lost.
Once back at the Museum, conservators excavated one of the cauldrons by removing soil using a small spatula or scalpel. Pre-existing cracks made the cauldron very weak and the base was not connected to the sides, having corroded and become detached during burial. It was decided that, due to the cracks and the objects’ fragility, the sides of the cauldron would be removed in order to allow conservators to excavate the interior.
To do this, a support was made for each section so the cauldron could be reassembled when full conservation is complete. The first section was then removed by excavating soil away from the interior wall and below the rim. It was then carefully lifted away from the cauldron and the interior cleaned with a scalpel to remove soil and corrosion. Breaks within the detached sections were dismantled piece by piece and reassembled, while areas of loss were filled to secure the structure. The exterior was then cleaned with a scalpel and aluminium oxide airabrasive.
Further conservation, scientific analysis and research of all 12 cauldrons will answer important questions including: when they were buried and why; where they were made, and what they were used for.