The Alum Industry of Carlton Bank

It is difficult to imagine that 250 years ago this tranquil scene was a hub of intense industrial activity. For over a century, Jurassic shales were quarried here to produce alum crystals, which were essential as a mordant in dyeing textiles and as a curing agent in tanning¹NYMNPA HER Records CARLTON BANK ALUM WORKS HER No: 6208.

A comment on a previous post about how the alum was transported and its destination prompted me to walk up to Carlton Moor this morning to take this photograph.

The finished product would be transported by sea to merchants in London, Hull, and even Liverpool. The sea would also be used for necessary bulk inputs such as coal, timber, and metals. Being an inland location, packhorses were used at Carlton to carry the alum to the ships.

The large bowl in the photo illustrates the volume quarried. At Carlton, the shale strata was 35 yards thick, with an additional 25 yards of overburden. The shale underwent a lengthy process to produce alum crystals.

Alum is a double salt of aluminum sulphate combined with either ammonium or potassium. Its value was known to the Egyptians and Romans, but its production was once shrouded in mystery. Traditionally made through a complex, dangerous process involving minerals and urine, alum production was a papal monopoly until Henry VIII. English expertise and espionage then led to an industrial boom in North East Yorkshire. I have posted about the process before, but a recap may be useful.

First, a clamp was formed by alternating layers of shale and a fuel, either wood or coal, encased in clay. This was set alight and left to burn for several months. The result was calcined shale, which was then repeatedly steeped in tanks of water to dissolve the alum salts. At Carlton, archaeological excavations suggest three distinct sets of steeping pits, each approximately 11 metres long, 4.5 metres wide, and one metre deep. When the salt solution reached the right specific gravity, it was channelled to the ‘Alum House’, where it was mixed with urine and left to crystallise. It took 50 tons of shale to produce one ton of alum.

Carlton’s Alum House was located far below, near the isolated tree in the field to the left in the photo²NYMNPA HER Records CARLTON BANK ALUM HOUSE HER No: 6560 . At Great Ayton and Kirby, a wooden channel was constructed, and it seems likely that a similar one was used at Carlton. There is evidence of a rectangular earthwork with embankments, possibly indicating the site of a reservoir used for water collection at the Alum House³NYMNPA HER Records Reservoir at Carlton Bank HER No: 8074 .

The process illustrates the risks and rewards of the enterprise. It would take a year before any return on the investment was seen.

Source:

Appleton, Peter. “A Forgotten Industry. The alum shale industry of north-east Yorkshire”. Boroughgate Books. 2018. Appendix 5. ISBN 978-0-9933674-1-0.

• 1
  NYMNPA HER Records CARLTON BANK ALUM WORKS HER No: 6208
• 2
  NYMNPA HER Records CARLTON BANK ALUM HOUSE HER No: 6560
• 3
  NYMNPA HER Records Reservoir at Carlton Bank HER No: 8074