Colour (5ml) is a simple test where the colour of the fluid is compared to set standards of a given scale from 1 to 8 with increasing darkness.
Tested On: Usually Steam and Gas Turbines. However, any lubricant sample can potentially benefit from this test.
Diagnostic significance: As an oil oxidises the colour will begin to darken/change and a colour change can often be one of the first indicators of early oxidation. The absolute colour is not significant, but the trend compared to previous samples is measured. Increasing darkness usually indicates other investigative tests should be performed such as Acid Number and antioxidant testing by RULER or RPVOT. Colour change may not always be significant as a small increase in acid number can still cause a noticeable change in colour, hence it should only be used in conjunction with other analysis data and not as the sole diagnostic flag.