Alum is a chemical named aluminum potassium sulphate; it inclines to be white powder with many uses, comprising:
i.) Like an antibacterial
ii.) Like an astringent
iii.) Like a 'Styptic pencil' to heal shaving cuts
iv.) Like a food preservative
v.) Cuts Soaked into materials to make them flame retardant
vi.) To stem the flow of minor blood loss
There are another uses, but these are some of common.