The sink-float comparator method of test for glass density provides the most accurate (yet convenient for practical applications) method of evaluating the density of small pieces or specimens of glass. The data obtained are useful for daily quality control of production, acceptance or rejection under specifications, and for special purposes in research and development.

Although this test scope is limited to a density range from 1.1 to 3.3 g/cm³, it may be extended (in principle) to higher densities by the use of other miscible liquids (Test Method F 77) such as water and thallium malonate-formate (approximately 5.0 g/cm³). The stability of the liquid and the precision of the test may be reduced somewhat, however, at higher densities.