In an attempt to purify 20 Muleteam Borax powder, I dissolved about 1.5 cup into about a quart of hot distilled water. Then I covered the jar let it slowly cool, in a styrofoam box. Very little material recrystallized at the bottom, so I put it in the refrigerator to force more crystallization.
Weird effect #1 But a day later, there was only a slight increase in crystal mass, but with tiny seed crystals forming all over the sides of the jar. So I left it there for a week, and the seed crystals just grew, very slowly. And they were quite well formed and clear.
Weird effect #2. I poured about 1/4 cup of the solution off (because the jar was very full and easy to spill). The next morning, there was a large increase in crystal mass, and the neat crystals were covered in a lot of chaotic crystal growth.
Weird effect #3. Two days later, the jar cracked and most of the remaining solution drained. Where the glass cracked, there is a definite protrusion of the side of the glass from the bottom. I can't say whether the side is pushed out, or the bottom is pulled in. This is a canning jar, so it should be well annealed and resistant to thermal shock.
I can guess that supersaturation was involved in weird effect one and two, but what effect broke the jar?