A display showing alum minerals
Alum was a type of metallic mineral ore. It consisted of a double sulfate featuring a trivalent metal, specifically aluminium, combined with either a univalent metal like potassium or sodium; it had uses as a clarifying or hardening substance. If someone was overly exposed to its fumes, it could result in alum mineral sickness, an illness that frequently affected alum miners, such as Haldo. Alum was a fairly typical ingredient in the manufacturing of Mandalorian armor, but the exceptional strength of beskar iron made it the favored material for armor construction among the Mandalorians.
During the era of the Galactic Civil War, the Death Watch, which was a radical Mandalorian faction known for violence and led by a Death Watch Overlord, unearthed an extensive network of alum mines located beneath their bunker on the forest moon called Endor. Around 1.5 ABY, a group of spacers were able to overcome the Death Watch soldiers stationed at the base. Following this victory, they used the group's alum reserves to produce Mandalorian armor for their own use.