Process for forming double picture prints on hard surfaces

摘要

The process is esp. suitable as a security system in design of coins, medals etc. and consists of producing a relief on the surface formed by a series of straight parallel grooves whose walls having a fixed inclination to the plane of the surface. The grooves are identical in size and shape and pref. of isosceles triangular section. A low-relief design is engraved in a given zone on the walls inclined in one direction, and another design engraved in the same zone on the walls facing in the other direction. The walls have a considerably greater inclination in the zones participating in the design.