Black Nab Alum Quarry

 quarry, 17th century construction

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This quarry was in use intermittently from 1649 until about 1791. The site was used for the extraction of alum principally for use in the textile industry as a fixing agent for clothing dyes. It was also used by tanners to produce supple leather. After the shale had been quarried it was then heaped into large mounds, fired and left to smoulder for up to nine months. The shale was then tipped into leaching tanks where it was left to soak in water. The solution, containing aluminium sulphate was then drained off and ran along stone or wooden conduits known as liquor troughs to the alum house. Here the water was boiled away from the solution in evaporating pans. An alkali, derived from human urine or burnt kelp, was added to cause precipitation of the alum crystals. The crystals were then bagged and transported for sale. The burnt shale left in the leaching pits was either disposed of nearby to form enormous shale tips or thrown in to the sea. The Black Nab Quarry was a much smaller operation than Saltwick Nab but the seaward side of the quarry is protected by breakwaters and the remains of a dock can be seen on the foreshore. The site also has evidence of a liquor trough, spoil heaps and possible steeping pits under the quarry floor.

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