Alum Crystals
Alum (aluminium potassium sulphate) crystals are among the easiest crystals to grow at home. The chemical used--alum--is a common compound that is available at the grocery store. Alum is nontoxic and can be used to grow a big, colorless crystal.
Borax Crystals
Borax is another household chemical which can be used to grow colorless crystals at home. Borax is found in the laundry soap section of the supermarket.
Charcoal Crystal Garden
Charcoal can be used as a base to grow a garden of crystals, which may be colored with food coloring. Ammonia and salt are also needed to grow this kind of crystal. The ingredients and the growing garden are toxic, so they should be kept away from young children and pets.
Potassium Ferricyanide Crystals
Red-colored crystals can be grown without the use of dye, from potassium ferricyanide. Children should not be allowed to eat or drink the chemical and its aqueous solution, but it is safe to dispose of in a household drain.
Potassium Dichromate Crystals
Potassium dichromate crystals grow in a natural orange color. These crystals are more difficult to grow at home, and due to their toxicity should not be ingested or touched. The crystals and solution must be disposed of safely.