Yep, alum will mess up every kind of unguant, lather, soap or ointment known. Denaturises the lot of 'em. If you use it before putting on a thick, gloopy AS balm, it suddenly become thin and runny like water. With shave creams or lather it will completely soak up the soapiness. I've noticed the same effect with styptic. If I get a couple of blood spots during the shave, I'll apply the Pinaud liquid styptic. Stops the bleeding fine, but if you try to lather up over where you put the styptic, the lather just dies on your brush.
