How to Grow Bismuth Crystals

Growing bismuth crystals is an easy, fun science experiment

Bismuth is a crystalline white metal, with a pink tinge. The iridescent color of this bismuth crystal is the result of a thin oxide layer on its surface.
Bismuth is a crystalline white metal, with a pink tinge. The iridescent color of this bismuth crystal is the result of a thin oxide layer on its surface. Karin Rollett-Vlcek / Getty Images

Bismuth is one of the easiest and prettiest metal crystals that you can grow yourself. The crystals have a complex and fascinating geometric hopper form and are rainbow-colored from the oxide layer that quickly forms on them. Follow these step-by-step instructions to grow your own bismuth crystals.

Bismuth Crystal Materials

  • bismuth [find at Amazon]
  • 2 stainless steel measuring cups or aluminum cans that you have cut in half to make shallow bowls
  • a stove, hot plate, or propane torch

You have a few options for obtaining bismuth. You can use non-lead fishing sinkers (for example, Eagle Claw makes non-lead sinkers using bismuth), you can use non-lead ammunition (the shot will say it is made from bismuth on the label), or you can buy bismuth metal. The quality of crystals you obtain depends in part on the purity of the metal, so make sure you are using bismuth and not an alloy. One way to be certain of the purity is to remelt a crystal of bismuth. It can be used over and over again.

Grow Bismuth Crystals

Bismuth has a low melting point (271°C or 520°F), so it is easy to melt over high cooking heating. You are going to grow the crystals by melting the bismuth in a metal 'dish' (which will have a higher melting point than the bismuth), separate the pure bismuth from its impurities, allow the bismuth to crystallize, and pour away the remaining liquid bismuth from the crystals before it freezes around the crystals.

None of this is difficult, but it takes some practice to get the cooling time just right. Don't worry—if your bismuth freezes you can remelt it and try again. Here are the steps in detail:

  • Place the bismuth in one of your metal 'dishes' and heat it over high heat until it melts. It's a good idea to wear gloves since you are producing a molten metal, which is not going to do you any favors if it splashes onto your skin. You'll see a skin on the surface of the bismuth, which is normal.
  • Preheat the other metal container. Carefully pour the melted bismuth into the heated clean container. You want to pour the clean bismuth out from under the gray skin, which contains impurities which would negatively affect your crystals.
  • Set the clean bismuth in its new container on a heat-insulated surface (e.g., set the container back on the burner, but turn the power off). The cooling rate of the bismuth affects the size and structure of the resulting crystals, so you can play with this factor. Generally, slower cooling produces larger crystals. You do not want to cool the bismuth until it is solid!
  • When the bismuth has started to solidify, you want to pour the remaining liquid bismuth away from the solid crystals. This happens after about 30 seconds of cooling. You can tell it is about the right time to pour the liquid away from your crystals when the bismuth is set, but has just a little jiggle to it when jarred. Sounds scientific, right?
  • Once the crystals have cooled, you can snap them out of the metal container. If you are not satisfied with the appearance of your crystals, remelt and cool the metal until it is just right.
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Your Citation
Helmenstine, Anne Marie, Ph.D. "How to Grow Bismuth Crystals." ThoughtCo, Apr. 5, 2017, Helmenstine, Anne Marie, Ph.D. (2017, April 5). How to Grow Bismuth Crystals. Retrieved from Helmenstine, Anne Marie, Ph.D. "How to Grow Bismuth Crystals." ThoughtCo. (accessed February 24, 2018).