Fylingdales

From 1650 to 1850, Peak (now Ravenscar) was a thriving hub of alum production. Alum is a crystal containing aluminium sulphate produced by a chemical process. It was ground into a powder and used as a fixing agent in the textile dyeing industry and as a preservative for tanning leather. A by-product of the alum production process was Epsom Salts, which were used in the manufacture of medicines.

Peak was an ideal location. The vast amounts of alum shale needed for the process could be quarried from nearby hills, and other necessary materials such as human urine and seaweed were easily brought in by boat.

Alum was one of Britain's first chemical industries. Following the discovery of alum-bearing shale in North Yorkshire, over 30 alum-producing sites were established in the 17th and 18th centuries. By 1780, they were producing 5000 tons of alum a year. At Peak, output was about 10% of the total.

The site came into the care of the National Trust in 1979. Clearing the area revealed some of the most extensive remains of any alum works in Yorkshire. Prior to our visit today, I knew nothing about alum. I found the whole story of this little known industry absolutely fascinating!

Alum production was very labour intensive. Up to 150 men worked at Peak in appalling conditions. They were housed in tiny rooms below the quarries and worked for up to 16 hours a day in a hot, noisy, smelly environment. Life expectancy for such workers was very low.

Over 100 men quarried the shale. They had to dig 100 tons of shale to produce just one ton of alum. Before the shale could be extracted, though, they first had to remove tons of unwanted soil and rock. Once they had the shale, 'barrowmen' collected it and carted it on raised walkways to the base of the quarry. Here, brushwood was used to ignite heaps of shale 100 foot high and 200 foot long. These 'clamps' burnt for almost a year, turning the grey shale bright red and producing an acid that converted the aluminium sulphate in the shale to a soluble form.

The shale was then tipped into shallow stone-lined seeping pits. The 'liquorman' then washed it with water to produce a raw alum liquor. This was then channelled from the pits to the quarry cisterns. From there, it passed down a wooden trough to the Alum House, where it was stored in preparation for the crystallisation process. The 'pitmen' had the arduous task of emptying the pits, which each contained up to 60 tons of wet shale.

The process of converting the alum from a liquid to a solid crystal took 3 weeks. The liquor was boiled and then left to stand, allowing any impurities to settle. It was then boiled again for a further 24 hours until it turned a syrupy green. It was left to settle again before an alkali (either potash derived from burnt seaweed or stale human urine) was added.

After 4 days, the first alum crystals had formed. These were washed to remove any remaining impurities before being placed in a roaching pan, a covered stone chest lined with lead where steam dissolved the crystals. The resulting strong liquor was then left to crystallise again in wooden roaching casks. After a further 8 days, the crystals had formed a solid block weighing over a ton. The cask was then dismantled, and the block was left to stand for another 8 days. Any remaining liquor in the centre of the block was drained by drilling a hole in it. This liquid was reused.

Finally, the alum block was ground into alum 'flour' ready for transporting to the rest of Britain and Europe.Les mer