Between youtube, personal websites and the mailing lists there is a bit of information regarding the basic process of growing the crystals from bismuth.
The physical process driving the formation of hopper crystals is that while cooling the edges attract more molecules than the center.
This site has a nice general over view of bismuth and some good photos of close ups of crystals.
The basic process is as simple as melt, pause, pour.
A couple of youtube videos that demonstrate the process.
This one seemed like the most realistic Edisonian demonstration. At the end before the commercials, there is a close up of a couple of small crystals with good color.
This video clearly demonstrates the need for high purity bismuth. The hopper crystals still formed, but the entire block still has a bronze color without any of the iridescence.
In this video you can see the beautiful colors from the oxidation. There is a built in lesson in there, the interiors of the the crystals are not cleaned. Care needs to be taken to "shake" the liquid out before it cools covering the details.
Those cover the basics, the details for growing larger crystals took some actual reading.
I read a lot of things and this was the most comprehensive first hand knowledge of achieving decent results.
But after reading it I think for the best results, using a flow hood with a shield gas, and something simple like an aquarium pump to color the crystals before they cool past the critical temperature.
Some testing will need to be done.
Some data on cooling rates/size
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