This small dish of crystals was made from the reagent-grade metal that is the first sample under bismuth. Ed Pegg and I had made several nicer ones long before, but I wanted to make a video showing how you let the metal partially harden, then pour off the still-molten center to reveal the crystals forming from the bottom and outside.
For some reason, this time the metal behaved quite differently. It may have become contaminated with enough of an impurity (lead?) to change its characteristics, or the difference may have had to do with the fact that I was using a plumber's propane torch to heat it, rather than an electric kiln as before.
(I wasn't exactly being careful to control the conditions, as making this video was another one of the things I had to do between bouts of child care.)
In any case, the biggest difference was that this time, it did not form the pretty colored oxide layers. Instead the metal stayed absolutely bright, forming only a dull gray oxide film that was easily skimmed off before it started cooling.
The other difference was that the crystals were smaller, though they were still obviously bismuth-shaped square hopper crystals. This is almost certainly due to less-clean cups and more contamination in the form of particles that initiate crystals from many places at once.
Still, I got a decent dish of crystals, and a decent video of it. Click the story book icon for more details on the procedure for making the crystals.
Source: Theodore Gray
Contributor: Theodore Gray
Acquired: 11 August, 2002