Convert glossiness measurements to Miscellaneous angles

Is there a way to convert a gloss measurement at one angle to a gloss measurement at a different angle? For example, you may need to use a single angle gloss instrument and need to report the gloss to one of your customers at a different angle.

The chart below can be found in the BYK-Gardner catalog and used in various PowerPoint presentations, but is worth showing and explaining again.

For this case study, 13 samples were visually ranked from matte to high gloss and measured with 3 specified gloss geometries. Photo courtesy of BYK-Gardner.

We state that if the gloss measured on a 60° meter is less than 10 GU, then 85°C should be used. Why? Take a look at the chart above. Samples 1-13 visually separated the same gloss difference. This means that the difference between sample 2 and sample 3 looks about the same as the difference between samples 6 and 7 or between 12 and 13. However, the gloss profile at a measurement angle of 60° drops significantly less than 10 GU when measured. Likewise, the curve flattens as the gloss exceeds 70 GU. Between 10 and 70GU, each sample has about 15GU spacing (10, 25, 40, 55 and 70). But below 10 GU, the first 5 samples are unevenly spaced, with a maximum of only 10 GU.

If you look at measurements below 10 GU (60°) using the 85° measurement angle, the samples will again approach this 15 GU spacing: 3, 18, 30, 47, and 60 GU. Likewise, once the curve flattened out by hitting about 70 GU at 60° meters, we lost 15 GU of pitch. Switching to a 20° measurement angle gives us a gloss of about 25 GU (70 GU at 60°) and brings the scale up to 40, 55, 70 and 88 GU. The visual spacing of the gloss panels again correlates well with the numbers obtained on the gauges.

But how do you convert a 60° gloss reading (say 0.5 GU) to an 85° gloss reading for a customer specification. The 85° measurement for this sample can range from 3 GU to 10 GU. The specs are usually tighter than that. What is the 20° gloss value for a sample measuring 10 GU at 85°? What about the 20° gloss value for a sample measuring 45 GU on an 85° meter? I think you can see the problem.

None of these values ​​can be converted. The way to measure gloss correctly and accurately is to use a proper gloss meter.