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10:57am on Friday, 5th August, 2005:



Alum is a salt used to fix dye to cloth. It's old — the Romans used it — and was traditionally very expensive. In the Middle Ages, England was a huge producer of wool but had to import the alum it needed to dye it (from the Middle East and — until the Reformation — the Papal states). It wasn't until the turn of the 17th Century that England managed to create its own alum works (at Carlton, near Whitby).

Here's how alum was made:

What I want to know is how, in ancient times, people figured out that if they did this they'd get some stuff that would fix dye to cloth.

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Copyright © 2005 Richard Bartle (richard@mud.co.uk).