A process of producing an article having a surface provided with an optical
diffraction grating such that the surface generates visible color when
illuminated with diffuse white light. The process involves deforming a
starting material to produce the article having the surface and, during
the deforming step, impressing a diffraction relief pattern on the surface
by a tool provided with a bearing surface having a corresponding surface
relief pattern of parallel lines that contacts the surface of the article
under pressure. While the diffraction relief patter is being impressed,
the surface is caused to slide in a direction of movement relative to the
bearing surface of the tool. The invention also relates to the article.
