Alum Clamp, Ayton Bank

The small knoll in the photo is an alum clamp, a relic of an 18c chemical industry to produce alum.

Alum had many uses: medicinal, in tanning to make leather supple and durable, as a mordant in dyeing cloth. It does occur naturally and is known to have been used by the Greeks but on Ayton Bank and in other parts of Cleveland and North Yorkshire it took a long and complex chemical process to produce alum from the Jurassic shales found here.

First a clamp is formed, alternating layers of shale and a fuel, wood or coal. This is set alight and left to burn for several months. The result is calculated shale which is then repeatedly steeped in tanks of water. When the solution is of a specific gravity it is then mixed with urine, I kid you not, and left to crystallise. It took 50 tons of shale to produce 1 ton of alum.

By the 1770s the price of alum had plummeted, the works at Ayton Banks closed virtually overnight and this clamp was left burning in situ. Perhaps there was some hope that it could be reopened later when the price recovered. It is believed to be the only intact clamp remaining.

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