FTM 3005 (FED-STD-791 Method 3005) Dirt Count of Grease
In this method, “dirt” refers to particles that are unintentionally present in grease. Dirt may come from many sources including the environment, contamination in raw materials, debris from packaging, and products of degradation or dimerization resulting from aging or improper storage. This method determines the size and concentration of opaque, or dark body, particles in grease. (Translucent and other semi-opaque particles cannot be distinguished from the structure of the grease.)
A microscope slide coated with test grease at a specified uniform thickness is covered with a cover glass and examined under a microscope. Particles are measured and counted. Reported are the number of particles from 25 to 75 micrometers, 75 to 125 micrometers and greater than 125 micrometers per cubic centimeter of grease.