ASTM D128 (Paragraph 7.1) Analysis of Lubricating Greases – Ash Content
Ash producing substances in lubricating greases may originate from either additives (typically molybdenum or zinc compounds) or contaminants (from packaging, environment or other sources). This method determines the percent of ash producing substances in lubricating grease.
The sample is placed in a clean, dried, crucible, heated, ignited to remove all organic components, cooled and weighed. The percent ash is reported. If sulfated ash is of interest (as in greases containing metallic additives) the sample is ignited in a crucible as above, treated with sulfuric acid, heated to allow the sulfating reaction to occur, dried and weighed. The percent sulfated ash is reported.