Fineness inspection
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.
