The method is used to determine the diameter of colorants formed by pigment and toner grinding under certain pressure and temperature conditions after a certain period of time. Materials and equipment include round Glass, metal fixing disc, syringe, ink suction tube, transparent measuring scale, weight, Ink knife, flat mill, fixed clock and equality. For inorganic pigments, weigh the master standard and mix with toner grinding. After grinding for a certain number of revolutions, take the colorants and put them into round Glass. After a certain period of time at a certain temperature, measure its diameter with a transparent measuring scale.