The Mining of Alum
Alum is used in paper manufacture and in the tanning industry.
Britain's alum supplies came mainly from Papal and Spanish mines,
Henry VIII was not happy with that.
But attempts, made between 1545 and the end of the century, to produce alum here all failed.
until Thomas Chaloner had some success at Guisborough in North Yorkshire;
Then in 1607 new sources were discovered at Ravenscar.
As a result of these finds alum works sprang up all along the Yorkshire coast,
Men, working down the cliff, dug out the gray alum-bearing shale, This was heaped onto a bed of brushwood about a metre. thick. The brushwood was set alight. The shale was then built up on top to form a clamp of  12 to 30 metres high, This would burn slowly for up to a year. to produce active water-soluble sulphate from pyrites (iron sulphide) in the shale, this converted  the aluminium silicates into a water-soluble aluminium sulphate.   
 The colour of the shale  changed from gray to pink;
The  shale was then put to drain in stone pits to extract the soluble aluminium sulphate  for several days.
then passed from the tank in wooden channels  to the raw liquor cistern situated near the plant, where it was processed.
At this stage the liquor contained iron and magnesium salts as well as the aluminium sulphate.
The next step was to clarify and concentrate the liquor, here it was brought to the boil for twenty-four hours in open lead pans, the concentrated liquor was then passed to a lead-lined settling tank.
to remove most of the yellow iron silicate.
Once clarified, it flowed by gravity into the Cleared Liquor Cistern.
The  liquor was then subjected to further evaporation in lead pans the contents being reduced to about one third of the original volume by boiling for 12-24 hours.
The concentrated liquor at this point contained sulphates of aluminium, iron and magnesium.
A quantity of alkali (potash from kelp or ammonia from urine),  was added to the liquor before passing it to the Cooling House.
The object of adding the alkali was to convert the aluminium sulphate into the double salt with its unique solubility characteristics. The liquor was allowed to cool in shallow tanks
The solubility of alum decreases sharply as the temperature falls. As a result small alum crystals are formed.
The crude alum crystals were then dug out and washed with cold water .
Alum has the useful property of having a low solubility in cold water in contrast to the other impurities
still in solution.
This principle is exploited in the final stage of separating the alum from the other constituents.
The crude alum crystals were re dissolved in very hot water and transferred to large casks
and allowed to cool.
The alum crystallizes out leaving any remaining impurities still in solution.
The  casks were made up of lead-lined wooden sections which could be assembled or dismantled as required. The casks and their contents were allowed to stand for eight days, then the sections were removed, exposing a crystalline mass.