You should not use Alum (white powder sold in grocery stores and for film and paper hardeners) for hardening emulsions that are going to be coated. You can use it in food. Ian is correct in that there are several "alums" including Zirconium which is called Zircotan.

Alum, or Potassium Aluminum Sulfate is rather harmless and has a LOT of pucker power. If you ingest it, your esophagus may close off but you will not be poisoned. Go to a poison control center or hospital.

All of the other Alums are poisonous. If you ingest any of them, go to a funeral director as quickly as possible. (Just kidding, but it is not good. It is much worse than any of the others.) Chrome alum is bright blue, kinda like grape juice. It is the worst of a bad lot.

None should be banned AFAIK and that price is very high. Check the price at the Formulary.

PE