4.1 This test method is useful in determining the approximate amount of nonvolatile inorganic material in leather. This may be in the form of salts or oxides of the elements. In a mixed chrome tannage, the approximate percentage of other elements in the leather may be determined by subtracting the chromic oxide that may be conveniently determined on the ash. (See Test Method D2807.)

4.2 The temperature of 600 °C specified is high enough to produce a reproducible result but it does not completely dehydrate such oxides as aluminum oxide, (Al₂O₃) and chromic oxide (Cr₂O₃). Likewise, such salts as sulfates and phosphates may be incompletely dehydrated, and if alkalis and chromium are present simultaneously, oxidation to chromate may occur. Therefore, caution is advised in drawing conclusions based on quantitative relations of the elements.