PURPOSE: To form a stain-proof film on a surface of the metal simultaneously with a removing of the stain by a method wherein an organic stain-preventive agent of 1W 30wt% is contained in the resin particles for use in a sand blasting operation, the agent is formed to a granular shape in integral with the resin so as to perform a blasting operation.

CONSTITUTION: As a resin, thermo-plastic resin or thermo-setting urethane resin etc. such as polyethylene polypropyrene etc. is applied. Shape of the resin particle is not restricted, but a spherical or a cylindrical shape of the resin particle having a particle diameter of 0.1W5mm is selected. Organic stain-preventive agent is not particularly restricted, but a gaseous agent may be selected. Irrespective of the kind of metal, a surface active agent of anion group is applied. Due to its gasification characteristic, a workpiece such as a die having a complex shape may be coated efficiently at once after the blasting operation is performed.