Is potash alum good for skin?

My mother used the alum powder and rub it over her face since she was young. Back home during her time, there's no such thing as cream or lotion especially when she was poor and lived in a third world country. Her skin at the age of 66 still glowing and tight. Never once had any breaks out. She only use regular bar soup and some time apply lotion, regular body lotion or just use the alum powder. She keep telling me not to waste money in all those fancy and expense facial cream. Also another recommendation she gave me is to use it as muth wash. Put a tiny piece of alum in your mouth (no water) for 5-10 minutes. What it does is it brighten your teeth and eliminates bad breath. I tried that and it does work way better than mouth wash. It doesn't whiten your teeth like magic but if you do it every day, you'll see the difference. Only con is that the tasting is very sour. I pick up this product at the Asian store for less than $2.00 for a 10 oz cube. Hope this helps. My mother is a living proof. My skin is not any where near a 66 years old woman's skin. Very clear and healthy without spending a dime on skincare product.