This is a smart fun-damental science project from Rimstar, and I like the plexiglass window on the styrofoam container for looking inside without needing to remove the lid:
The basic idea is to create a supersaturated solution and grow the seed crystal in it. What’s a supersaturated solution? Well, we’ll be disolving some substance in distilled water. You may have done this when stirring salt, sugar or coffee in water. We’ll keep adding that substance and stirring until no more can be disolved. Any additional substance we add just stays as the substance sitting in the bottom — it doesn’t disappear into the water. At that point we say the solution, the water and whatever we’ve disolved into it, is saturated. It’s saturated when we can’t disolved any more.
But, if we heat up the solution, then we can disolve some more into it. And when it cools down again, the solution is now supersaturated.
Why do we need a supersaturated solution? Why can’t we just put the seed crystal in a saturated solution? A solution that’s saturated has a stable mix of the distilled water and the substance. It’s at equilibrium. Since it’s a stable mix, there’s no reason for the substance to come out of the solution and grow on the seed crystal.