The particle size of glaze and body slips are checked for residue on 44 and 63 microns (this test is done in all factories in the tile industry, for example). This measurement has proven practical for quality assurance purposes (keeping critical production parameters under control) because particle size distribution for wet grinding is theoretically akin to the Gaus distribution. Along with viscosity, this check provides practical particle size and surface area information without expensive instruments.
The percentage of material powder whose absolute particles are larger than 44 microns (325 mesh).63RS - +63 Micron Residue (V)
The percentage of material powder whose absolute particles are larger than 63 microns (230 mesh).