New glassware is so smooth that there are no nucleation sites available on the exposed surfaces. Also, new glassware from the manufacturer usually has a variety of dusty contaminants. If a sample only yields small crystals, the method should be altered so as to slow down the growth step. Slowing the crystal growth sometimes requires changing the method used to grow the crystals. Avoid vibrations near your growing crystals.
Some methods work in a few hours, and other methods require weeks or even months for success.
Evaporation Evaporation is by far one of the easiest methods for crystallizing organic and organometallic small molecule compounds. The choice of solvent is very important because it can greatly influence the mechanism of crystal growth and because the solvent may be incorporated into the crystalline lattice. It is customary to screen a large number of solvents or solvent mixtures to find the best conditions for crystal growth. The rate of crystal growth can be slowed either by reducing the rate of evaporation of the solvent or by cooling the solution. Formation of only a few rosette-shaped masses is an indication of an insufficient number of nucleation sites.