P2NP Recrystallization: Method for Purifying Substances 

To add to this, stirring continuosly while crystallizing is necessary in the absolute majority of cases to get a purer end product. Large Crystals are a sign of decent purity, but they can actually entrap mother liquor, and make it harder to wash out impurities. There is a balance that must be achieved here, stirring to vigorously leads to too small crystals that catch a lot of mother liquor on the surface and need to be washed more, but since the surface area is large, you will lose more yield. The correct balance is often only found experimentally, but "no stirring" is almost never the right answer, even though it seems to be done a lot. In industry, you stirr by default and only try not stirring in edge cases. I could get purity of an industrial product up from 99,0 % to 99,95 % just by finding the right crystallization - and stirrer conditions without changing anything else, this absolutely matters. (Cooling down slowly was also part of the enhanced procedure, you're absolutely right about that.)

Спасибо за коментарий. Нам это известно, пусть знают и остальные.