A single crystal placed in a specific solution to grow a larger crystal is known as a seed crystal, explains About.com. To grow a seed crystal, the chemical to be crystallized is needed, as well as water, a shallow dish, a heat source and nylon line.
When making the solution, it is important to know the solubility at specific temperatures of the chemical being used in order to estimate how much of the chemical is required. Solubility information also offers information about what to expect during cooling of the solution. If a substance is more soluble at a higher temperature than at a lower temperature, crystals grow as the solution is cooled. An example of such a crystal is a sugar crystal. On the other hand, if the solubility of the solution does not change much with temperature change, the crystals form during evaporation of the solution. A salt crystal is an example of this type of crystal. In these two examples, in one instance, the solution is cooled to grow the larger crystal and in the other instance the solution is kept warm to speed up evaporation, which is why knowing the solubility is so important when growing crystals.