Alum

Potassium aluminum sulfate, commonly known as 'alum,' is a widely used and ancient mordant for wool, silk, linen, cotton, and various other fibers. It helps fibers bond chemically with dyes, improving the wash fastness and lightfastness of natural dyes. Typically, it is recommended to use alum at a concentration of 10-15% WOF (Weight of Fiber).

Name: alum potassium sulfate

Other names: alum, potash alum, potassium aluminum sulfate

Formula: KAl(SO4)2·12H2O

Form: white powder

Safety: safe to use but do not ingest

Purpose: common mordant for protein and cellulose fibers. Additionally, can be used to make lake pigments from natural dyes, printing pastes, etc.

Here is a step-by-step recipe for mordanting fibers with alum.