There are quite a few classes relating to inspection criteria which go from AA to G.
Here are some reference documents for your research:
MIL-STD-1949 MAGNETIC PARTICLE INSPECTION
ASTM E 1444
AMS 3040 Magnetic Particle Inspection Material Dry Method
AMS 3044 Magnetic Particles, Fluorescent, Wet Method Dry Powder
AMS 3045 Magnetic Particles, Fluorescent, Wet Method Oil Vehicle