Alum: Alum is the most common and frequently used mordant for fastening the natural dye on cellulose fibres and textiles.
It is a chemical compound that protects the naturally dyed textile from light and provides it with good wash fastness.
Alum powder is recommended to fasten the colour of natural dyes on fabrics, as it will help the colour fade off when exposed to sunlight and water.
Mordant: Use alum at approximately 15 to 20% to the weight of the fabric.
Its results may vary as per percentage used and the fabric composition.