While picking up some spices at the grocery store, I noticed a container of alum powder. Could this be added to some witch hazel or mixed with water for use as an aftershave?
If you were ambitious you could Use the powder to supersaturate some water and grow yourself an alum crystal. I bet you could find a recipe somewhere on the interwebs. I am too lazy to bother searching for you.
According to Wikipedia and a couple sites selling it, culinary alum is just Potassium Alum. So I do believe it would work. I have no idea about appropriate concentrations for aftershave, I'll saturate water with alum for deodorant, which doesn't take a lot of alum. I'd guess about 1 tsp. per 4 ounces of water for my deodorant. I'd go much less for aftershave.
