The use of additives to improve the kinetics of layer crystallization is investigated in detail for the first time. An understanding of the process is obtained on the example of a synthetic binary glycerol-water mixture. Its application to 2 real industrial separation tasks, raw glycerol and paraffin, is also investigated. In aqueous glycerol, wb = 5% 1 butanol in a static crystallizer allowed increase of the growth rate by a factor 10 without loss in the separation success. Calculations reveal that the additive’s measured effect is caused not only by its influence on viscosity and diffusivity. It also enhances natural convection by concentration-polarization-induced density gradients and favourably changes the surface tension of the crystal layer. From this discussion, a protocol for choosing a suitable additive is derived. For glycerol, BuOH is a good, but not the ideal additive. However, its influence can be as large as the influence of an agitation stronger than that in a falling film.