Growing hopper-like bismuth single crystals

Bismuth is a beautiful metal to crystallize, producing distinctive stepped, hopper-like crystals with a striking geometric appearance. I have included a picture of a crystal I have grown myself. The process is simple: melt high-purity bismuth, cool it slowly, and carefully separate the crystals from the remaining melt. With a little patience, you can grow large, well-defined crystals using only a few basic pieces of equipment.

A hopper-like Bi crystal grown in Liverpool, UK.

1. Get high-purity Bi metal — ideally 99.99%+.
2. Melt the Bi in a clean crucible at about 300–350 °C (Bi melts at 271.4 °C).
3. Hold just above the melting point until the melt is completely homogeneous.
4. Cool very slowly — roughly 0.5–2 °C/min through the crystallization range.
5. As crystals form, stop stirring/disturbing the melt. Slow, undisturbed cooling favors large faceted crystals.
6. Decant the remaining liquid Bi while it is still molten, leaving the solid crystals behind.
7. Let the crystals cool completely to room temperature.
8. Break away excess Bi mechanically and select the crystals with well-developed stepped faces.

For especially large/clean crystals, repeat a melt–cool–decant cycle, using the best crystals as seeds.