Potassium alum also known as potash alum, or potassium aluminum sulfate is a chemical compound with formula KAl(SO4)2·12H2O. Alum is the common name for this chemical compound, given the nomenclature of potassium aluminum sulfate dodecahydrate.
It is commonly used in water purification, leather tanning, dyeing, fireproof textiles, and baking powder. It also has cosmetic uses as a deodorant, as an aftershave treatment and as a styptic for minor bleeding from shaving.
Potassium alum crystallizes in regular octahedra with flattened corners. Alum is commonly used in crystal growth experiments.