Apparatus for determining the size distribution of pigment particles in a paint surface

An apparatus for determining fineness of pigment particles in a sample of a pigmented liquid, comprising:

• a grindometer block comprising a longitudinally extending sample channel of steadily increasing depth receptive of a sample to be investigated and which is stripped and smoothed with a doctor blade for examination, and means for examining the stripped and smoothed sample of the block comprising
• a) means for directing a light spot along a light path and onto the sample to be investigated to effect a scattering of light at pigment particles;
• b) photoreceiving means disposed in a light path of light directly reflected from the sample for producing light signals in response to light received thereby;
• c) means for blocking the light directly reflected by the sample from reaching the photoreceiving means and for directing scattered light to the photoreceiving means comprising an aperture diaphragm including a circular ring surface defining an aperture and a central circular surface and means for focusing light directly reflected by the sample into the aperture diaphragm at the central circular surface to block the passage of direct light through the aperture diaphragm and for directing scattered light emanating from pigment particles in the vicinity of the light spot to the aperture to permit the passage of scattered light through the aperture diaphragm and thereby to the photoreceiving means, whereby the photoreceiving means detects the scatted light passing through said aperture diaphragm to produce scatted light signals;
• and
• d) means for longitudinally scanning the sample channel with the light spot and comprising means for longitudinally displacing the grindometer block relative to the light spot.