The penetration test with post-emulsifiable, fluorescent penetrant (type I, method B & D) is the most complex test method, but guarantees the highest accuracy and the most reliable indication of errors. It is mainly used in the field of aerospace.

Post-emulsifiable penetrants cannot simply be removed from the test surface with water, but must be made washable using an emulsifier. The advantage is that the penetrant that has penetrated the flaws is very difficult to wash out, which minimizes the risk of overwashing.

A test system with post-emulsifiable penetrant consists of:

• penetrant
• emulsifier
• cleaner and
• developer