Crude indanthrone is milled, with or without other additives, to reduce and normalize particle size and distribution to a sub-pigmentary, near amorphous, state. The resulting highly aggregated crude powder is then treated with a heterogeneous solvent system of water and an alkyl ester of an aromatic carboxylic acid, such as methyl benzoate, to de-aggregate and grow the particles back to a pigmentary size. The conditions of the solvent treatment can be controlled with respect to temperature, time, and solvent ratio such that the desired properties of strength, shade, and dispersability are optimized.