Chrome alum or chromium alum is a safe salt that produces dark, purplish crystals. It can be mixed with Potassium Alum to create almost any purple color you want!
- An alum is a type of chemical compound with the general formula XAl(SO4)2·12H2O, where X is a monovalent cation such as potassium or ammonium
- Alum crystals form octahedral shapes in their purest form
- Mixed Chrome Alum crystals consist of potassium alum (KAl(SO4)2·12H2O) mixed with chrome alum (KCr(SO4)2·12H2O)
How to Grow Chrome Alum Crystals
- Start by preparing two saturated salt solutions – one for each alum salt. This is done by heating distilled water in a beaker to near boiling and dissolving a maximum amount of salt in it. After cooling to room temperature the solution can be filtered.
- Mix both the colorless alum and the dark greenish chrome alum solution. The ratio is for you to experiment: using more chrome alum solution will yield a darker purple color.
- For growing large single crystals, a seed crystal can be prepared and then placed in the solution for further growth.