[hodwik]

Got it. It's like honey crystals.

They force other crystals to be of the same size and shape.

(That's why creamed honey producers put a "starter" crystal in, which is tiny, that forces the honey to produce other tiny crystals.)

[adrianN]

I wonder what the mechanism in honey is. Normally if you put seed crystals in saturated solutions they'll just grow bigger.

[hodwik]

If you find out please report back. Couldn't find information on it.