Crystal formation is a result of a material substance arrange in a particular regular pattern. The combination of crystal shapes and lattice dimensions can uniquely identify a substance. Crystals of table salt (sodium chloride), for example,
look cubic whether it is grown in nature or in the laboratory. To a non-scientist, crystals of a substance seem to grow in a variety of shapes. This is because, in this world, nothing seems to be perfect. There are numerous
factors that can affect a crystal growth: gravity, dusts and other contaminants, temperature change etc. Despite these effects, the fundamental crystal unit cells are still retained and there are scientific instrumentations (such as X-ray diffraction technique) able to detect characteristic of crystal faces.
In this site we will not discuss the scientific details of crystals. In fact, it is the above mentioned factors that make crystal growth to be fun and sometimes unpredictable. It is rather easy to grow small crystals, in this section we will look at procedures to grow large crystals, using copper sulfate and Rochelle's salt as examples.
General Growth procedure
There are two general procedure for growing large crystals. In both cases, a seed crystal is placed in a jar containing the solution:
(i) Sealed jar method: The solution is supersaturated it and seal the jar.
(ii) Evaporation method: Saturated solution is allowed to evaporate slowly.
In both cases, maintaining a constant temperature is important. We will look at the evaporation method since it is easier to do. One way to minimize temperature change is to place the jar in pile of water, taking care not to spill the water into the solution. Since the water rises and falls in temperature more slowly than the surrounding air, it will act as
a 'thermal blanket' reducing (but not eliminate!) the temperature fluctuation of the immersed jar.