| 摘要 |
A security mark is applied to the surface of an article by:- (a) providing a smooth finish to the surface (1) of the article; (b) applying a retroreflective surface layer (3) comprising transparent spherical particles (5) embedded in a transparent binder (2), at least one area (A) of said layer having said particles (5) spaced from the smooth-finished surface (1) by a separation comparable to the focal lengths of the particles, and at least one other area (B) having the particles spaced from the smooth-finished surface (1) by a separation noticably less than the focal lengths of the particles. When viewed in light incident generally perpendicular to the surface, the areas A appear bright and the areas B appear dark. With light incident at an appreciable angle to the surface, the bright and dark areas are reversed. <IMAGE> |
