Sub-micrometric particles of pigment blue 15:6 were successfully prepared via a continuous supercritical anti-solvent (SAS) process by using dimethyl sulfoxide (DMSO) as a solvent and supercritical carbon dioxide as an anti-solvent. The shape of the pigment's primary particles is rod-like with the minor axis length ranging from 50 to 80 nm and the major axis length from 200 nm to 1.0 mu m. As evidenced from Section 2.3, moderate concentrations of pigment solution, moderate pressures, and higher temperatures can effectively reduce the mean particle size. The precipitation kinetic parameters were determined from the particle size distributions with the aid of the population balance theory. The secondary nucleation was found to be dominant in the precipitation and diffusion may govern particle growth. (c) 2005 Elsevier B.V. All rights reserved.