I was wondering Martin if some of the coastal briquetage we find was
used for other than draining and drying salt. But from your description
would certainly not apply to alum. I guess the alkali was probably
Thanks for the reference it sounds like an interesting paper I should get.
On 4/26/01 1:45 AM Martin Roe writes:
>The manufacture of alum is a complex process which basically consists of
>extracting aluminium sulphate from the shale, mixing it with an alkali and
>then concentrating the mixture before allowing it to crystallise. The
>crystals are then purified.
>The so called Alum Shales comprise mostly alumina (aluminium oxide) but also
>contain iron pyrites. Shale was quarried and then buned in heap was around
>200ft long and up to 100ft high (sounds familar but without the cows and
>sheep!). The heap was kept burning slowly for upto a year. This roasted or
>calcined the shale converting the iron pyrites into sulphuric acid which
>combined with the alumina to form aluminium sulphate which was then combined
>with a suitable alkali.
>Huge quantities of shale were required by the works, about 100 tons was
>needed to make 3 tons of alum crystals.
>For a fuller account and details of sites see Gary Marshall's
>paper published in Industrial Archaeology Review vol XVII no 1 Autumn 1995,
>"Redressing the Balance - an archaeological evaluation of North Yorkshire's
>Coastal Alum Industry.
>NAMHO Conference 2001-MINING HISTORY and BEYOND
>Lead Mining in the Yorkshire Dales
>The Industrial Archaeology of Halifax
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Beatrice Hopkinson 73071,327@compuserve