It's the tannins in coffee and tea that allow them to dye stuff.
Nancy (from Texas) to my knowledge salting is archival. It's salt- the oldest known preservative in the world. I would not suggest trying a salting technique with dyed or scented bath salts, but you can use a variety of different grades of salts to create different effects.
Check out my little gray mouse to see effects caused by a fine grained salt. Now, you don't want to get it wet after it's dried, but then you wouldn't want to get any art wet after it's completed. Salting has been used by artist for quite a while with fantastic results. Different molecular makeup than acid. It's not going to eat your paper and I've never had a problem with it turning an odd color either. Kate
Sunrise Workshop & Gallery, the Art of Kathryn M. Pinkham.