This specification establishes the classification, technical requirements, tests, and test procedures for the qualification, approval, and quality verification of all materials used in the liquid penetrant methods of inspection with the exception of those excluded in the application section. AMS2644G results from a Five-Year Review and update of this specification. This revision adds a separate category for Method A Water Containing penetrants “Method A(W)” (1.4.1), adds a reference to D3828 (2.2), updates the toxicity characteristics review requirements (3.2.3), defines requirements for formulation certification and requalification (3.2.4 and 3.2.7), updates safety (3.3.1) and the flash point test requirements for penetrant materials (3.3.3), updates the water tolerance test for Method A, Method B, Method C, and D penetrants (3.3.8.5), adds maximum water content requirement for Method B emulsifiers (3.3.9.6), clarifies the developer dispersibility test requirements for aerosols (3.3.10.5), modifies the sensitivity acceptance criteria for initial qualification and requalification Method A and Method A(W) penetrants(4.4.5.1.6), updates the Reference Material List (Tables 1 and 2), Sensitivity qualification matrix (Table 3), and Removability qualification matrix (Table 4).