Abstract: A method of detecting the quality or damage and/or deterioration of a coating when applied to a clean surface, the coating (6) consisting essentially of a paint into which is mixed a luminescent pigment additive which is less than 10% by weight, the luminescent additive being much less than that used for known luminescent paints where the level of luminescent pigment is as much as 45%. The coating (6) is illuminated by means of a projector (4) with ultraviolet light; the coating then being viewed for gaps or variations in the intensity of the luminescence of the image. The image is then preferably digitally recorded for detailed analysis and subsequent reference. The coating and method are advantageously used on surfaces which are difficult to view, such as ships' ballast tanks or tall structures such as bridges.