David, Jess, and I don’t really know anything about crystal formation, but here’s what we do know:
Soylent Green is people.
When you run out of ice at a party, and you’re trying to make more, and you’re checking the tray like every fifteen minutes while drinking warm gins-and-tonic, and then near the end of the night you start using the half-frozen cubes: There’s ice on the outside and a juicy core of water on the inside. This makes sense; the outside of the cube must get cold first.
This guy will sell you water crystals, or pictures of them, or something. He makes them himself. Or, if you want to participate in the mysteries, he’ll sell you some highly-charged hexagonally structured concentrate.
The bulk of any crystal is formed by stray molecules latching on to already crystalized ones. We’re told that the air/water surface, tray surface irregularities, and impurities in the water make good primary nucleation points for the crystal.
After you’ve been sitting a while, get up, stretch, walk around. It’s good for a body.
Thoughts on growing a perfect crystal:
We read somewhere that restaurants make clear ice cubes by freezing them progressively in thin layers (rather than all at once in a big cube).
Growing an ice cube that’s a perfect crystal—that is, where all molecules in the ice cube conform to the same crystalline pattern—would probably involve using scratch-free trays, purified water, and some kind of seed crystal or progressive freezing process like the restaurants use. The cube that resulted would probably be hard and transparent. It’s not obvious, though, that such a cube would pop easily out of an ice cube tray.
Apparently, growing a perfect ice crystal is not easy.
A reader sent me a link to this page, which explains that the cloud at the center of the ice cube is gas that is squeezed to the middle by the freezing process. “You may have seen the large blocks of crystal-clear ice used by artists who carve ice sculptures. Icehouses make these large blocks of clear ice by continuously removing the ‘gassy’ water from the middle of the block with a pipe and replacing it with degassed water until the block is completely frozen.”
Thoughts on growing a strong crystal:
Metal alloys (metals with intentionally-introduced impurities) are strong crystals not because they are perfect, but because they are made of lots of little tiny crystal grains that lock together well.
Growing a fine-grained ice cube would probably involve lots of impurities—sugar-water, perhaps?—or spraying water in many fine droplets or packing snow with a glacier or something. The resulting cube would probably be hard and opaque. It’s not clear that this kind of cube would pop easily out of a tray, either. Maybe it would, maybe it wouldn’t.
Before we go any further, let’s have some more gratuitous pictures of ice cubes. Have a gander at these beauties.
The first dim view of the world as seen by a baby cube emerging from its watery mother.
Later, when the maturing cube’s sight organs have shed their nascent film, it can see clearly as far as the freezer door.
One day, the hand will reach into the freezer.
Two cubes, one shattered by forces beyond its control, contemplate fleeting time and the sunset from the vantage of a blue plate.
An ice spike.
Also notice how the tops of these cubes have protruded from the tray; apparently the top froze first, and then the expansion of the lower part of the cube (as it froze) raised the top part out of the tray.
Some of the ultimate variables affecting our crystal formation are these:
There are a number of proximate variables which we can more directly affect:
The idea is that the proximate variables can be expressed in terms of the ultimate variables: For instance, the type of tray might ultimately be changing the number and location of nucleation sites (because of scratches or material irregularities), the local temperature gradient (because of the heat conduction of the material of the tray and the extent to which it allows evaporation), and the overall freezing rate (because of similar factors).
After a few experiments, David, Jess, and I chose a set of variables which we felt allowed for a nice range of possibilities without consuming too much time or effort. The variables are described as they are used, on the next page. No doubt we would get more sophisticated hypotheses if we had experimented using more (or better) variables. But it’s good enough for rock-and-roll, and we got pretty good results using the variables we used.