FAQ: "I do not know how to use ASTM D1500 Dilution Factor and when we need to use this item. Could you provide an explanation?"
Usually highly chromatic oil additives and lubricants can be measured as sold (default ASTM Dilution = 0 indicating there is no dilution of sample). However, on rare occasions, an oil product such as asphalt pitch is so dense and dark that you cannot see (and the instrument cannot measure) through such a dense product.
This type of product will have to be diluted with a solvent to some ratio in order to obtain useable color measurements. Dilution will affect the reported ASTM D1500 color for samples measured in the 33-mm path length cell, as well as the sample preparation method.
ASTM D1500 Dilution Factor must be reported with the ASTM D1500-33 mm only if the User has to dilute a highly chromatic sample to get a meaningful color measurement.
FAQ: "How do I determine what Dilution Factor is appropriate for my sample."
You standardize on the 33 mm cell filled with a clear, colorless solvent, typically distilled water. If you read this back as a PQ Performance Qualification step, the ASTM D1500 Color should read should read 0.2 closely with L* = 100.0, a* = 0, b* = 0 D65/10. The overall transmittance level for the cell and solvent should be 100%.
Measure you sample undiluted and if highly chromatic and dark, it will have a very low average transmittance value, say 5%.
Empirically determine a dilution factor (ex: 2:1, 3:1, 5:1) such that the average transmittance value is in the 30% - 40% range or higher. This will allow the ASTM D1500 Color measurement to discriminate lot color differences when this would not have been possible in the undiluted state.
Enter and report the ASTM D1500 Dilution Factor along with your ASTM D1500 Color value.