D.M. Yebra, C.E. Weinell, in Advances in Marine Antifouling Coatings and Technologies, 2009. 13.3.2 Grinding or breakdown of particle clusters. Pigment particles do not usually exist as primary particles but instead as aggregates or agglomerates. Reduction of these clusters to primary particles is necessary in order to obtain optimum visual, economic and performance properties of pigments.