Alum is on of the most commonly used mordants. It will improve wash- and light fastness on any fabric. Alum is called 'the sunny mordant' because it tends to brighten the colours. It will make yellows bright yellow and is a must for bright reds when dyeing with madder.
 
Recommended use is WOF 15-20% on protein fibers. For wool, alum should be used in combination with 6% WOF cream of tartar
For mordanting cellulose fibers, it is better to use Aluminium Acetate, Aluminium Lactate or Aluminium Tri-Formate.
 
 
Appearance: Odourless white granules that dissolve easily in hot water.
Potassium Aluminium Sulfate is an inorganic salt that has no harmful effects to the environment, pets or humans in small dosages. Potassium alum is considered by the FDA as a generally recognized as a safe (GRAS) substance.