1. Alum has been used in food processing. Just yesterday I saw alum sold
in grocery store in one of those spice racks. The description is
that it is used for pickling.
2. The Chinese has been using alum for sizing their watercolor paper for
thousands of years, and many of the painting last until today. Many
of them did turned yellow, and I think that is caused by the
acidity of the paper used.
David Soemarko