ZP-4D is a noncombustible dry powder developer for form A penetrant testing that is ideal for highly sensitive fluorescent penetrant processes. ZP-4D is applied to oven dried parts following the use of penetrants and forms a thin film on parts that enhances the visibility of ultra-fine discontinuities.

ZP-4D is listed on the QPL SAE AMS 2644 Qualified Product List and is approved for use by Pratt & Whitney.