PURPOSE: To enable engraving the pattern of the predetermined shape properly and finely on the surface of a base material and prevent the clogging of an injection nozzle in sand blasting by carrying a pattern part of abrasion resistant synthetic resin on a porous sheet of abrasive synthetic resin.

CONSTITUTION: A masking material 11 is bonded to the surface of a base material to be sand blasted, via an adhesive and the like, and subjected to a sand blasting process. In this case, the part of the base material surface covered with a pattern part 12 comprising abrasion resistant synthetic resin in the masking material 11 is free from sand blasting. Other parts of the base material surface are eliminated together with a porous sheet 2 comprising abrasive synthetic resin, and the pattern of the predetermined shape is thereby engraved. According to the aforesaid sand blasting process, the abrasive synthetic resin is crushed into fine powder and not entangled, thereby making an abradant free to enter an injection nozzle. Furthermore, the porous sheet 2 is not transparent and hardly give halation when exposed to light.