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I feel like this is probably a pretty elementary problem, but I haven't been able to find a solution yet. Basically, if I have an object with subsurface scattering on the material node using Principled BSDF, and another object intersects/occludes it, it causes strong discoloration around that object in the opposite color that the SSS color is supposed to be, even with a small subsurface radius. I recreated this issue using simple shapes below, but in practice, this is causing problems for a character bust I'm working on, where the character's skin has SSS and this discoloration issue is occurring heavily where the eyeball intersects the eyelid, and where the hair intersects/clips through the face, so half of the character's forehead looks blue.

overlapping objects with subsurface scattering issue

refrigerizer
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  • This is a known limitation of SSS, basically dued to the BVH handling of the SSS closure. If there are two (or more) objects intersecting, it will fail. If both geometries belong to the same object then Random-Walk will fail, but Christensen-Burley will work ok. The solution is to Boolean-Union all meshes into one closed surface. – Secrop Dec 12 '22 at 07:46
  • @Secrop Thanks for the info! If I merge the two objects (i.e. the 'head' sculpt, which has SSS on to emulate skin, and the hair object which doesn't have SSS) can I then only apply SSS to part of the now-single object or will it all have to have SSS applied? – refrigerizer Dec 14 '22 at 21:54
  • You may use material slots.. On the object that will get the boolean modifier, add an empty material slot. The modifier will then apply the material from the other object to that slot on the first one. – Secrop Dec 14 '22 at 22:56

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