Bismuth crystal creations by Stefan.

Bismuth is element #83 on the Periodic Table of Elements. It is known as a post-transition metal. It has a relatively low melting-point of about 520 degrees F, which makes it easy to work with. Bismuth crystals form when the metal begins to cool from a molten state. The iridescent colors that bismuth crystals are usually known for are the result of an oxide tarnish.
Although it is relatively easy to make bismuth crystals, making high-quality crystals is a bit more difficult. First, you’ll need several pounds of bismuth (99.99% pure). Second, a heating process. You can use a lab-quality heating plate, but you can also achieve the same results on a kitchen stove. Third is the extraction method. How you extract the crystals from the molten metal directly affects the types of crystals you create. Lastly, the cooling method. How quickly or slowly the crystal cools determines its colors.