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I have a problem with black areas on an object with Glass BSDF material.

Don't know where they come from, I stripped my scene down to be very simple to show you the problem...

Created the object with Blenders spin tool, I checked thickness of the glass and normals, seems fine to me.

Read that this could happen when smoothing the object, tried with flatten, no change.

Here the blend: http://www.wesp.de/blender/test.blend

enter image description here

Thanks for your help to identify / solve the problem.

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3 Answers 3

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Solved the problem with a work-around nodes solution instead of the straight glass BDSF. Maybe not straight physically, but looks better in this case.

Thanks to all for your advices. enter image description here

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  • $\begingroup$ This Node Setup is "better" in this case at least and looks much better than the Glass BSDF. $\endgroup$
    – Michael
    Nov 20, 2016 at 14:17
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    $\begingroup$ But I agree, this is a quick fix, and should not be neccessary. I really tried to find the reason for the problem (increased "glossy", "reflections" and other parameters, built up white walls on all sides, changed the Environment map, checked the model itself ... to be sure that the black reflections are NOT physically OK), but couldn't find the reason. $\endgroup$
    – Michael
    Nov 20, 2016 at 14:38
  • $\begingroup$ Edited according uhoh's advice. He's right. $\endgroup$
    – Michael
    Nov 23, 2016 at 18:53
  • $\begingroup$ Congrats on your solution! I think it's great you took the time to post it here for the benefit of others. $\endgroup$
    – uhoh
    Nov 24, 2016 at 1:10
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Read my answer here Black holes / Water in glass

Glass does have "black areas"

Any image on the internet will have those areas enter image description here

If you really want to reduce them, try playing with the IOR value of the glass, or change the thickness.

The effect is also less noticeable if you have a nice background.

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  • $\begingroup$ Thanks, tried playing with the IOR, there are noticable effects (expectable), but didnt solve the problem. $\endgroup$
    – Michael
    Nov 8, 2016 at 12:56
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As @10replies pointed out, these are natural. The dark areas are really showing you views of the actual dark areas of your background by a combination of refraction and total internal reflection. A mirror would do the same thing in the right orientation.

If you don't like the black, you have to fill the dark areas with something that is emitting at least reflecting light. As a quick test, I added more light on the sides (red and green) and you can see some of the black areas turn red and green.

enter image description here enter image description here

enter image description here

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  • $\begingroup$ Hi, OK, built up white walls around the whole scene, also ceiling and floor so there is nothing black what could cause these ugly, un-natural reflections. Same ugly black reflections. Could it be the model of the glass itself? (I noticed no errors there, (normals and so on...), also tried not to smooth the object, applied my subdivision modifier, and played around with the edge split modifier. No better results. Is it possible that cycles has problems with glass itself? $\endgroup$
    – Michael
    Nov 8, 2016 at 13:01
  • $\begingroup$ Trying different node setups now... I will post the results.. $\endgroup$
    – Michael
    Nov 8, 2016 at 13:22
  • $\begingroup$ How many reflections are you allowing. Some paths may have many many reflections inside the glass. $\endgroup$
    – uhoh
    Nov 8, 2016 at 13:31
  • $\begingroup$ Nothing special: wesp.de/blender/lightPaths.png , but i have tried to increase all values $\endgroup$
    – Michael
    Nov 8, 2016 at 13:38
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    $\begingroup$ I'll keep the number of bounces in mind, thank you. Now testing different Node setups for the Glass Material, .... $\endgroup$
    – Michael
    Nov 8, 2016 at 14:13

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