Alum
Defined as hydrated potassium aluminum sulfate, the material known as alum comes in several chemical combinations. It occurs naturally in the desert southwest and was discovered by early silversmiths as a pickling agent to clean the surface of silver. The folklore of alum is very ancient, and the stuff has been used to remove freckles, as an antibiotic for wounds, to make pickles crisp, as a mordant to set natural dyes and in leather tanning. A pure form is available now to clean silver, eliminating fire scale and oxidation. It leaves silver a flat, white color, removing the metallic gloss, which is why the Zunis call silver hek’ohanna or tsi: hewe—white iron. The natural alum is called ma’atza.