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Why is Glass material displayed fine on one object, but material with exactly the same settings shows some kind of nonsense on another? For example, glass of car. The one shown above has transparent glass, while the one below is black & has curved glass reflections. I tried to add Subsurf, tried changing Light path settings, turned off Auto smooth, tried different glass settings, but nothing helped. And this happens often. Please tell me what it depends on & how to fix it?

enter image description here

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  • $\begingroup$ Your Glass material behaviour the same for me. Clear Custom Split Normal Data and add Solidify modifier. $\endgroup$ – vklidu Jan 27 at 8:04
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In provided blend both materials behaves the same for me.

Anyway ... bottom one seems to be correct from material setup perspective. Glass needs a thickness otherwise cycles thinks it is an "endless" glass volume.

enter image description here

Since you add s thickness like Solidify modifier, Cycles know where glass begins and where ends its depth. But as you can see there is some issue with normal orientation.

enter image description here

Go to Data Properties > Geometry Data > Clear Custom Split Normal Data

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I guess, this is result you are expecting from glass material.

enter image description here

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  • $\begingroup$ I hadn't noticed the custom normals .. I guess they might be a Data Transfer from a more heavily subdivided mesh, for economy? $\endgroup$ – Robin Betts Jan 27 at 8:41
  • $\begingroup$ Yes, this is exactly what I need. Thank you very much for your help! $\endgroup$ – Juliya Jan 27 at 9:01
  • $\begingroup$ @RobinBetts Probably ... I'm not such experienced with Normals, I just saw the "crazy" reaction of Solidify, that didnt react on Auto Smooth :) $\endgroup$ – vklidu Jan 27 at 9:24
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The simulation of refraction depends on light rays being bent twice. Once on the way into the glass, via a front-facing surface, and once on the way out, through a back-facing surface. Your 'good' glass has thickness, so it works. Your 'bad' glass doesn't.

No thickness:

enter image description here

With a Solidify modifier: (No rim. 'Fill' unchecked, so as not to bother with normals interpolating over the rim walls)

enter image description here

If you want a rim on your glass, you will have to bevel it too, to sharpen the interpolation of normals from rim to surface.

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  • $\begingroup$ It worked! Now glass looks like it should. Thank you so much! $\endgroup$ – Juliya Jan 27 at 9:02
  • $\begingroup$ @Robin Betts Since your images are more illustrative ... if you extend your answer about Clear Normal Data info ... I'm ready to delete my answer :) $\endgroup$ – vklidu Jan 27 at 9:32
  • $\begingroup$ @vklidu IMO your answer is just fine! (UV'd). I didn't clear the normals, because the only distortion I got was from the interpolation to the rim of the Solidify modifier. So my way was just to solidify without the rim, which can't be seen, until the OP rolls down the windows :) $\endgroup$ – Robin Betts Jan 27 at 10:58
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    $\begingroup$ I know ... I just that both answers are speaking in general about same thing ... I wanted to keep it cleaner, but OK. I still live in an illusion we are creating a "cookbook" where people can find solutions for their repetitive issues ... but it is an illusion ... we are still answering the same questions. Even for me (after a few years here) it is almost impossible to find same (already asked) question ... so instead of spending time on searching of dupli, we creates new one. Grrr $\endgroup$ – vklidu Jan 27 at 11:15
  • $\begingroup$ Yup. maybe I should just have left the 'rim' point as a comment on your answer, and not posted. You were first, and accepted. I'll look out more carefully in future. $\endgroup$ – Robin Betts Jan 27 at 11:37

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