Particle perylene pigments

Since perylene pigments are only sparingly soluble in common solvents, the solvent conditioning of crudes is commonly done under harsh conditions. For example, a common method to adjust the particle size and morphology of a perylene... 

Add pasting is a pigmentation process in which perylene crude is dissolved in concentrated (>90%) sulfuric add, and then reconstituted by precipitation under precisely controlled conditions, to produce a pigment with the desired physical charaderistics. Add swelling is a similar process, except that 75-85 % sulfuric add is used to partially solubilize the cmde and give an equilibration between the smallest and largest particles of the mass this is followed by predpitation under controlled conditions. 

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