Hercules Un-Purple Primer is designed to be used anywhere that regular purple primer can be used. Instead of being colored purple, a clear primer with a unique patented ultraviolet sensitive ingredient reveals its purple presence under UV light, helping to prevent staining and the resulting property damage. Un-Purple Primer is designed to work identically to other PVC/CPVC primers. No new technique is involved in the installation or testing. Simply apply as any other primers would be used. Hercules Un-Purple Primer goes on completely clear. Hercules Un-Purple Primer meets standards established by the American Society for Testing and Materials (ASTM) and is certified by the National Sanitation Foundation (NSF), and International Code Council Evaluation Services (ICC ES PMG). Many local codes, including the Uniform Plumbing Code of the International Association of Plumbing and Mechanical Officials (IAPMO) reference the ASTM standards. High Intensity pocket-sized UV flashlights and keychain UV flashlights with batteries are also available. When using UnPurple Primer, the installer must have a UV flashlight or other UV light available for the inspector's use. Primer color: Clear. Label color: Green.