This method involves the measurement of the ratio of the mass of the residue to the mass of the sample after passing the pigment through a sieve of a specific pore size, expressed as a percentage. The required materials and equipment include sieve, Zhongkai wool pen, Balance, electric blast box and 95% ethanol. The determination method includes method A, that is, wet sieve method. The specific steps are to weigh 10g of the sample, put it into a sieve wetting with ethanol, then wetting the sample with ethanol, holding the upper end of the sieve, immerse the bottom of the sieve in water, and gently brush it with Zhongkai wool pen until there are no pigment particles in the water. Then rinse twice with distillation water and once with ethanol. Finally into (105 +/- 2) ℃ thermostatic oven baking for 2 hours, quickly removed into the dryer chilled down to room temperature weighing until constant weight.