Actually I have used alum on a kard and it does being out the little subtlties. It is still in progress. What I do is have a dish with a little water and a lot more alum until it becomes a watery paste, heat the mixture, and apply with a brush or rag (use distilled water). It will take lots of time, but the results are interesting. Water and alum make a weak acid. Hope this helps. I would only use this with wootz from India or Persia.
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