The scratch standard (MIL-O-13830A) is a cosmetic standard effected by a visual comparison with a set of secondary standards that are in turn evaluated by comparison with a set of master standards. Both manufacture and certification of the secondary standards are somewhat unreliable. This paper shows that they can be classified according to the relative power scattered at a relatively small angle and describes experiments with etched gratings that have the appearance of scratches but diffract light into a broad peak between 5 and 10° off the axis of the incident beam. Some prototypes have been classified both by comparison to the master standards and by a photoelectric measurement; agreement between the two methods is good. Such gratings, used as the secondary standards, should display less intersample variation than scribed or other artifacts. The paper concludes by presenting evidence that the original primary standards have been stable over a long time.
Matt Young, "Scratch-and-dig standard revisited," Appl. Opt. 25, 1922-1929 (1986)