Sculpting in solid mercury, with some help from liquid nitrogen

How to cast solid, if fleeting, shapes in mercury: just keep it at 320 degrees below zero.
A fish sculpture made out of mercury that's been frozen by liquid nitrogen.
Frozen fish: The frost crust forms when water condenses from the air. Mike Walker

What you consider solid, liquid or gas depends entirely on where you live. For example, men from cold, cold Mars might build their houses out of ice. Women from Venus, where the average temperature is about 870 degrees Fahrenheit, could bathe in liquid zinc.

We think mercury is a liquid metal, but it’s all relative. At one temperature, the mercury atoms arrange themselves into a solid crystal; at another, they flow freely around each other as a liquid. Children from Pluto (like mine, for example) could happily cast their toy soldiers out of mercury, because on that frigid planet it is a solid, malleable metal a lot like tin. Here on temperate Earth, you need a stove to cast tin, but a tank of liquid nitrogen to make mercury figurines.

Achtung! Theodore Gray is a scientist trained in lab safety procedures. Do not attempt this experiment at home. For more information on Gray’s scientific pursuits, visit his website, and see much more mad science in his book: Theo Gray’s Mad Science: Experiments You Can Do at Home but Probably Shouldn’t.

At liquid-nitrogen temperature, about –320 degrees Fahrenheit, mercury acts like any other metal: You can hammer it, file it, saw it. (It won’t shatter like other liquid-nitrogen-frozen items because there’s not enough moisture inside.) Watching it solidify is exactly like watching tin harden from a molten state. As the atoms go from liquid to solid crystal form, you see the surface pucker. And because mercury, like most metals, shrinks when it solidifies, you see the surface sink in areas, forming a patchwork characteristic of cast metal.

The fun of making frozen mercury trinkets is another reason to lament the fact that this marvelous metal is also an insidious poison that must be handled carefully and never spilled. Schools have been evacuated because of one broken mercury thermometer, and mercury in the environment, particularly in fish, is a major public-health concern. Which is, of course, why I made this cute little mercury fish.