Evaporation affects crystal growth by allowing or not allowing the atoms to form the correct crystal structure. In a rapid evaporation, some atoms will arrange in a crystal, however because there was not much time for growth, the crystals will be small, and end up in a powder like end product. With much longer evaporation times (days to weeks), atoms will arrange in a crystal, with no impurities (atoms that do not belong in the crystal). These crystals will be much larger and able to be picked up for analysis.