Optically active additive (OAA) is an organic or inorganic material which, when added to a coating, makes that coating react to ultraviolet light. This effect enables quick, non-invasive inspection of very large coated areas during the application process allowing the coating inspector to identify and concentrate on defective areas, thus reducing inspection time while assuring the probability of good application and coverage. It works by highlighting holidays and pin-holes, areas of over and under application as well as giving the opportunity for crack detection and identification of early coating deterioration through life. The use of optically active additives or fluorescing additives is specified in US Military Specification MIL-SPEC-23236C. The use of OAAs and the inspection technique is described in the SSPC document Technology Up-date 11.