Quote Originally Posted by thebigspendur View Post
There are two types of Alum. Potassium and Ammonium. Usually the deodorant is the Ammonium type which is kind of strong for the shave. Potassium is way more gentle and is what we use for shaving.
True there are two types. Crystal brand, that sells deodorant stones, sells both kinds, so you might want to read the labels before purchasing. I personally have the Crystal stone that is Ammonium alum and use it on my face without issue. It stings no more than aftershave.