ASTM D128 Analysis of Lubricating Grease Percent Soap
Grease is a lubricating oil with a thickener. One common thickener is metallic soap (including sodium, calcium and lithium soaps), which tend to be relatively inexpensive, and may be formulated to give water resistance, thermal stability, shear stability or other attributes. This test determines the percent soap in a grease.
The grease undergoes a series of physical and chemical separation steps which vary depending on the type of grease. The percent soap is calculated and reported.