Some of the most important factors for crystal growth are the solubility of the solute in the solvent chosen for crystallization, the number of available nucleation sites, and time. The increase in temperature during crystal growth increases the evaporation rate of the solvent, thus accelerating the growth rate. Crystals grow faster in warmer temperatures because the liquid containing the dissolved material evaporates quickly. Although somewhat exotic, convection can be a good method for growing high-quality crystals.
The generation of a temperature gradient in the crystallization vessel by cooling or heating part of it leads to a slow and constant flow within the liquid phase. The idea is that more substance dissolves in the hottest part of the container and travels to the colder region where it begins to crystallize. The crystals move with the current and travel to the hotter zone, where they completely or partially dissolve. Those that only partially dissolve will grow on their next trip from warm to cold and warm up again.
Several hundred cartridges can create a glass of good diffraction quality. The velocity in the vessel is proportional to the heat gradient, which should not be too large, since too fast a convection will not leave enough time for nucleation. Under the old Garbage In %3D Garbage Out rule, a crystal structure is only as good as the glass used for data collection. Remove the smaller, larger, better-looking crystals from the saucer to use them as a crystal seed.
Most crystals are the same shape and size and look a lot like each other, but you've probably seen some crystals on the paper that look a little different. Small holes reduce the maximum resolution at which the crystal is diffracted, while larger holes destroy the glass. There are many factors that affect crystal growth, so crystal projects are great for scientific experimentation and science fairs. Temperature and humidity are two factors that affect evaporation rate, so you could design an experiment to see how different temperatures and humidity levels affect the rate of crystal growth and the size of crystals.
These crystals are likely to have broken parts, or there may even be more than one glass glued together, making them look different from the others.