Abstract: A method for treating a gem stone to cause a marking thereon, wherein a photoresist resin is secured to the stone, a photographic film bearing the desired marking is applied over said resin, said resin is developed by exposing same to a light source, the exposed portions of said resin, as well as said film, are removed, and the thus-treated portion of the stone is subjected to a cathode bombardment in such a way that etching of the stone occurs in those locations which are not protected by said resin.