Abstract: A crystalline modification, designated ".beta.", of the dye of the structure ##STR1## The .beta.-crystalline modification of the dye is easier to isolate from water and gives filter cakes of higher solids and color content. The .beta.-form is also more suitable for making liquid formulations of the dye; the liquid formulations of the crystalline modification have lower viscosity and better dispersion stability than liquid formulations of non-modified form. The .beta.-modification of the dye is obtained by heating an aqueous slurry of the dye at about 90.degree.-95.degree. C. and pH of 8.5 to 9.5 until the modification is complete. The crystalline modification of the dye gives Debye-Scherrer X-ray diffraction patterns substantially different from the non-modified form.