Sunday, 3 April 2011


The remains of The Old  Alum Works at Ravenscar offer a glimpse into a lost industrial past peculiar to this part of the east coast. Indeed it could be seen as the birthplace of the British chemical industry. What made the development of this complicated process so astonishing is that the science of chemistry was still non-existant. Everything occured as a result of laborious trial and error.

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
Aluminium silicates and iron pyrites were both present in the Lias shales, a feature of the Yorkshire coast's local geology. To produce alum, the sulphur from the iron pyrites and the alumina from the aluminium silicates had to be combined in as pure a state as possible.

Alum shale was dug from two large quarries and burned in huge stacks on brushwood fires. The chemical reaction gave off its own heat, so more shale could be piled on until these smouldering mounds, called clamps, were sometimes as much as 20 metres high. They burned for a full nine months, after which the whole rock became red in colour.

The 'calcined' shale was then steeped in pits of water to extract aluminium sulphate. The liquor was run off into settling tanks and the remaining red rock, known as 'mine', was dumped either on or over the cliffs. These spoil heaps are now the preferred habitat of yellow flowered gorse bushes.

One of the stone drainage channels
The liquor was then boiled in a Boiling House in pans over iron plates. This part of the process relied on huge quantities of coal which was brought to the works by sea. A stone lined winding house which once contained the winching machine remains at Ravenscar, iron fittings and spindle wheels still intact. It was used to haul coal deliveries up the cliff, and to load the finished alum product onto ships in the dock below.

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
In the heyday of urine usage people put it out on their doorsteps in jars ready for collection, buckets stood on street corners and special urinals were built in cities for the purpose. It was shipped in from such places as Newcastle and London in barrels in lye boats.

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.

Peak alum works as it is today
(Click on the photo for a larger image)
The site is now owned by The National Trust and is free to visit. It is well signposted from the Cleveland Way.

1 comment:

groke said...

Extra urine for alum production needed to be shipped in, collected from the back yards of London, Hull, Newcastle and Sunderland. It was transported to Whitby in barrels. Some say the used barrels were then refilled with Yorkshire cheese and butter and sent straight back to London where it was appreciated for its distinctive flavour.. Chris C.