Alum was first produced at Slapewath, Guisborough in 1604. In 1640 Sir Bryan Cooke discovered alum in the rocks at Peak, now more commonly known as Ravenscar. The Peak fault, a shift in the rock strata that occured 350 million years ago, left accessible Lias shales above sea level to the north of Ravenscar, an obvious advantage if you wanted to mine it without drowning.
Alum was used as a mordant for fixing dyes and in the leather industry to render hide supple and manageable. During the 19th century synthetic alum was produced and aniline dyes were invented that didn't require a mordant to fix them. The last alum works to close were those in Kettleness and Boulby in 1871. The industry had lasted for around 250 years.
|The Old Alum Works, Ravenscar|
|One of the stone drainage channels|
The next stage of the process was to introduce potassium and ammonia. Potassium was obtained by burning kelp seaweed in huge quantities and adding the resulting lees to the mixture. As for ammonia, stale human urine was shipped into the works in huge barrels. It was said that poor people's urine was better as it was not the product of such strong drink.
|The Winding House|
When the potash and ammonia was added to the brew it was left to cool and alum crystals gradually formed. The liquor could be reboiled time and time again to maximize the yield.
The industry has left indelible scars on the local landscape. A burning floor on the cliff above Sandsend has left a large, desolate area of bare shale reminiscent of the lunar surface. Remains of stone breakwaters and berthing points can be seen at Saltwick Bay and in many places the entire profile of the cliffs has been changed by alum mining.