Home

Science HacksAdventures in Hacking Mother Nature 

Image of Bismuth Crystals

Home-Made Bismuth Crystals


This picture on the left shows some bismuth crystals I grew this summer. Bismuth is a metal that is easily molten and will form beautiful crystals when it solidifies. These hopper crystals, as they are known, naturally form into brightly colored cubes, intricate square spirals, or ziggurat-like pyramids. They are trully very alien looking.

I purchased about three pounds of 99.9% pure Bismuth metal from an eBay seller   Hallmark Metals. The price was $8.50 per pound, plus shipping. Shipping will bring the price up to about $12 per pound. I purchased two small LEE brand lead melting pots from JAX. These stainless steel pots, normally used for melting lead for shot-making, are about two-inches high and three-inches in diameter and hold about  200mL when filled to the brim (a little under a cup).

Melting the bismuth is surprizingly easy. I used a small portable electric range, although others have done this using their kitchen ranges as well. I erred on the side of caution and did it in my patio, placing the range in a large drip-pan as a precaution against any spills. I placed a one pound chunk of bismuth in the melting pot, turned the heat up to maximum and allowed it to heat up for about 20 minutes. When molten, the bismuth will flow just like mercury and resemble molten solder. It tends to form a crusty layer of slag, so it's handy to have something to scoop that off with. An L-shaped expansion slot cover from a computer worked nicely for me. I also had lengths of wire from an old coat hanger which I could form into various tools to poke and prod my molten brew.

Once the bismuth is fully molten, turn off the heat and it will solidify completely in about half an hour. If you do this, you will end up with a nice hockey-pucked shaped bismuth paper weight, which is only moderately interesting. Poking at it (with a long length of coat hanger wire and when wearing gloves, not with your bare hands!) as it solidifies will reveal much about the manner in which it hardens. You will notice that it forms a thin-crust at the surface, and solids will begin to form around the submerged insides of the pot, as these parts will cool off the most rapidly.

Coaxing crystals out of this requires some experimentation. One way is to allow it to cool for a few minutes (four minutes tends to work for my setup), then pour the molten bismuth into the other melting pot. What is left behind will be a shell of bismuth which hopefully have some crystals in it. One of my largest crystals formed on the cool sides of the lead pot as I poured the material from one pot to another. Another technique is to submerge the tips of short lengths of wire in the molten metal. These were attached to the bottom of a computer heat sink whose purpose was to draw heat away from the wire and hopefully promote the growth of crystals. The heat sink and wire are lifted after a couple minutes and hopefully crystals will have formed on the tips. A friend and I experimented with this technique and we had some moderate success with it.

Clean up is fairly straightforward. The solid bismuth, because it expands as it cools, tends not to stick to the pot very well, so you can easily pry it off one pot and combine it with whatever is left in the other pot. It is also easy to pry chunks of bismuth off your tools and remelt it with the rest. As you repeat the melting process over and over again, you will notice that a grayish crud tends to accumulate on the surface of the melt. This is a combination of pure bismuth and a rough, gray, flaky waste material that lacks a metalic luster. I scoop this out and dump it on a peice of tin foil for later triage. If it has significant shiny metalic parts in it, you may be able to extract pure bismuth from it by remelting, otherwise it is waste material.

Ingredients: