The second chief mechanism in crystallization is called secondary nucleation. In this phase of crystallization, crystal growth is initiated with contact. The contact can be between the solution and other crystals, a mixer blade, a pipe, a vessel wall, etc. Secondary nucleation can be thought of as the workhorse of crystallization. Again, no complete theory is available to model secondary nucleation and it's behavior can only be anticipated by experimentation.
Mathematic relationships do exist to correlate experimental data.
However, correlating experimental data to model crystallization is time consuming and often considered extreme for batch operations, but can easily be justified for continuous processes where larger capital expenditures are necessary. For batch operations, only preliminary data measurements are truly necessary. We have already covered one such method in our salt crystallization example. Cooling is one of the four most common methods of achieving supersaturation. It should be noted that cooling will only help reach supersaturation in systems where solubility and temperature are directly related.