The Screen Savers AppearancesPeriodic Table Table HomeI'll be appearing live on The Screen Savers (G4 network) at 7:00 PM Eastern, on Friday March 11, 2005. The topic is melting spoons: Should be fun. See their show listing for information about show times and reruns. If you've seen the show or read my Popular Science column on the same topic, and want to try making your own spoons, you'll need to overcome two main hurdles: Getting the ingredients to make the metal, and making the spoon mold. Getting the metals is the easier half. Indium and bismuth are routinely available on eBay: Just search for them and usually you'll find several listings. Tin is probably also available on eBay but it's much harder to find because you get a million listings for tin cans, etc, none of which are actually made of tin. Fortunately you can get it in the form of lead-free plumbing solder in any hardware store. (It's not pure tin, but it's close enough.) Indium will not be cheap: The last kilogram I watched sold for $610 and that was a below-market price. You need at least 50 grams to make a few spoons, 100g would be better. Bismuth and tin are cheap. You may also be able to find people selling pre-mixed low-melting solders (search for "low melting solder", "low temperature solder" and similar terms). Just look at the melting points to see if they will work, and watch out for anything containing lead, cadmium, mercury, etc. Mixtures containing gallium can have even lower melting points, but in my experience they are all sticky, staining skin and adhering to glass or plastic. After gathering the materials, you need to weigh out the correct proportions: 51% indium, 32.5% bismuth, and 16.5% tin by weight, measured reasonably accurately (within a percent or two would be good). Heat the stuff in a stainless steel measuring cup over an electric or gas stove, and stir until they melt together (you'll need to use a considerably higher temperature to get them to melt together the first time than is required to melt the alloy after it's made). Let it cool and then re-melt over a water double-boiler to be sure it's not too hot when you pour it into the mold. Now you're ready for the hard part: Making the spoon mold. (Or, I suppose, you could wimp out and buy a commercially prepared tin soldier mold or something. Since the temperature is so low you can use pretty much any mold, including ones meant for candy or chocolate. I just don't know of any source for spoon molds, because spoons are ordinarily stamped, not cast.) The mold I used on the show and for my Popular Science column was made with a clear jeweler's molding rubber that is lovely to work with, if you have a very accurate weighing balance and a vacuum pump. A much more user-friendly alternative is Quick-Sil, a two-part rubber compound you mix with your hands: It's virtually foolproof, at least in the mixing and hardening department. Quick-Sil is available from FDJ Tools a jewelry tools and supplies dealer that sells on the web. I can't really give full instructions for how to make a mold, but basically the idea is you find a spoon you like with a reasonably thick stem, mold the rubber around it, and when the rubber is hard you use a razor knife to ever so carefully slice the mold in half, freeing the spoon. There are many little tricks to doing this properly, and to making a mold that is properly vented to let air out while the metal is being poured in. You'll just have to experiment until you get it right, or find someone who's experienced in the technique. On March 1st, 2004 I was on the same Screen Savers show (when it was on the now-defunct Tech TV network), making liquid nitrogen ice cream. This is a result of the PR person at Popular Science where I write a column talking to a producer at Tech TV. Show notes are here and you can see streaming video by clicking on the link in the "Video Highlights" box. If you're here from the show and want more details about how to make liquid nitrogen ice cream, here are a couple of resources: If you actually want to try it, please be sure you know how to handle liquid nitrogen. The best thing is to find someone who is familiar with it, and also happens to have a Dewar flask for transporting it. Generally speaking it's not hard to buy liquid nitrogen from a welding supply shop, but you have to bring your own Dewar and they won't fill anything other than the proper kind (at least they shouldn't). You might find a welding shop that rents Dewars, or you can buy one for about $300. You can use just about any ice cream recipe you like, but don't put any alcohol in the mixture: That can depress the freezing point and result in smooth, creamy ice cream at a temperature that will freeze your tongue when you try to eat it. In the mean time, check out my periodic table table page: It's probably not what you think. |
