ASTM D1209 Color of Clear Liquids (Platinum-Cobalt Scale)
Highly refined lubricating oils are usually very pale yellow to colorless. Contaminated or less refined samples may have a darker yellow color. This test determines the degree of yellow in clear liquids using the Platinum-Cobalt (APHA color) scale which goes from 0 to 18 – a smaller number indicates a lighter color.
The sample is placed in the sample cell of a spectrophotometer. It is compared to a set of standard solutions, and the color that most closely matches the sample is reported.