Randomly Acquired Characteristic (RAC)
A feature or defect specific to one stamp that can occur in the manufacturing process or from individual usage occurring after manufacture (for example, wear and damage defects such as cuts and gouges, reproducible blemishes, impression voids, improper and extraneous inking, or coincidental peripheral printing). The position, orientation, size and shape of these characteristics are essential to the identification of a stamp as the source of an impression.