Here a very short tip or trick. It started with my question why satin looks so metallic while it is a dielectric. In almost all cases only a metallic can have a colored gloss/reflection. All other materials not. There are maybe more reasons why a material appears a bit metallic to the eye, but here an evidence that real geometrie has a strong inluence on the appearance of materials. In this case the second illustration appears to be a bit metallic to me. What happens is that the light is bouncing on the ridges, and turn back a colored gloss. Since we cannot expect to build all geometrie I think we are allowed to trick a bit and use a Metallicness function in our shader ( colored gloss) even for dielectrics. Which is in contradiction with the theorie that only metallics can have colored gloss/relfections.
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