The distance between the rollers determines the fineness of the grind. This process is run through for a maximum of five times. The finer the grind, the greater the tinting strength of the paint. The rollers are hollow and are cooled on the inside with water, as the pigments would otherwise burn through the heat of the friction. Depending on the nature of the pigment and the purpose of the paint or ink, the pigments are ground to between 2 and 55 microns (1 micron = 1/1000 mm). After the last grinding the paint finally has the required viscosity.
After the grinding the fineness is checked using the Hegman bar. The depth of the groove in the bar gradually increases, indicated in microns. The paint is thinned to a certain viscosity and then applied to the groove and levelled off. At the point where the pigment particles are larger than the thickness of the paint layer they stick up above the surface of the paint film. At this point, visible to the human eye under skimming light, the fineness is read off.