a uniform system for marking x - ray films with pertinent data . further , it establishes a technique for manufacturing x - ray markers which vary only slightly , so that by piggy - backing or stacking , virtually any thickness of marker can be obtained . in addition a method for making a transparent , adherent , and reusable marker is described . the markers are made of brass by a photo - chemical - etching technique and are coated with nickel in order to achieve permanency and contrast against a black plastic background for easy identification and storage .