Alum - WikiHQ

thumb|upright=1.5|Crystal of potassium alum,

An alum () is a type of chemical compound, usually a hydrated double sulfate salt of aluminium with the general formula , such that is a monovalent cation such as potassium or ammonium.

During the 19th century, alum was used along with other substances like plaster of Paris to adulterate certain food products, particularly bread. It was used to make lower-grade flour appear whiter, allowing the producers to spend less on whiter flour. Because it retains water, it would make the bread heavier, meaning that merchants could charge more for it in their shops. The amount of alum present in each loaf of bread could reach concentrations that would be toxic to humans and cause chronic diarrhoea, which could result in the death of young children.

Textiles and paper

Alum is used as a mordant in traditional textiles;