In this test, special three-inch copper strips are cleaned, polished and immersed into a test tube containing the oil being evaluated. The test tube is held in a water bath for three hours at 212ºF (100ºC). At the end of the exposure period, the strip is removed and cleaned. The strips are compared to a specially prepared set of standardized reference strips and rated against these standards on a scale of Class 1 (slight tarnish) to Class 4 (heavy tarnish).
An industrial gear lubricant that exhibits a 1b classification in this test is considered to exhibit good resistance corrosion to yellow metals.