DISAPPEARING ACT - A steaming cup of water liquefies the spoon in about 15 seconds - notice the puddle at the bottom of the cup. Photo: Jeff Sciortino.
With the right mix of metals, you can make an alloy that turns to liquid at nearly any temperature.
Mention liquid metal, and people immediately think of mercury. After all, it is the only metal that isn't solid at room temperature. Well, not quite - it's the only pure metal, but there are many alloys (mixtures of metals) that will melt well below that point. For example, the mercury-filled fever thermometers that children were told not to play with in the 1950s and '60s have been replaced by virtually identical ones containing the far less toxic Galinstan, a patented liquid alloy of gallium, indium and tin.
Those who were kids in that era may also remember playing with another low-melting-point alloy: trick spoons that melted when you tried to stir your coffee with them. These were made with a blend that, no surprise, was highly toxic; it typically contained cadmium, lead, mercury or all three. But, as it happens, it's possible to make alloys that liquefy in a hot drink using safer components.
A few months ago I created a batch of these prank spoons as a gift for my friend and fellow element buff Oliver Sacks (author of Awakenings
After the spoon turns to a puddle at the bottom of the cup, you can pour off the liquid and touch the metal, feeling the weird sensation of it hardening around your fingertip. When Sacks has used up all his spoons, he can easily recover the metal, melt it again over a cup of hot water, pour it into the mold, and make new ones - the trick-spoon circle of life.
So why can't you buy these nontoxic prank utensils in toy stores, as you could the toxic versions of years past? Price. Indium costs about three times as much as silver. (I get mine from a bulk supplier in China.) Using gallium, you can make alloys that melt in lukewarm water or even in your hand, but it's more expensive than indium, and it tends to stain the glass and discolor skin. Unfortunately, no alloy replicates the low cost, bright shine and nonstick fun of mercury. Too bad we know now that playing with it for too long can give you brain damage.
How To Create a Melting Spoon
| WHAT YOU NEED | ||
 Bismuth, indium and tin | Stainless-steel pan | Rubber or plastic spoon mold |
1
Make a mold by casting or forming jewelers' rubber around the object you want to duplicate.
2
Weigh out the metals in the correct ratio: 51 percent indium, 32.5 percent bismuth and 16.5 percent tin. If you're within a gram, it'll still work.
3
Combine the ingredients in a stainless-steel measuring cup and heat directly on a stove over low heat. You'll need to go well beyond the melting point of the final alloy in order to get the tin and bismuth to combine with the indium. Stir continuously.
4
Let the alloy cool, then reheat it over nearly boiling water. A double-boiler works, or you can just hold the measuring cup in the hot water for a minute or two.
5
Pour the molten metal into the mold. While it may be tempting to hold the mold in your hand, the metal is hot enough that it will burn if you spill too much on yourself. It is no more, but also not any less, dangerous than boiling water.
6
Wait until you are sure the metal has solidified in the mold. This may take longer than you think since the melting point is so low.
7
Carefully extract the spoon from the mold.
8
Enjoy! Stirred in nearly boiling water, a typical spoon will melt in seconds.
Source Official webpage: Gag with a Spoon