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I am using Cycles render engine. The glass material has a color of full white, roughness of 0 and an ior of 1.5. I was on a different forum given the suggestion to increase max bounces of the scene, currently i have 20 total, 4 diffuse, 20 glossy, 8 transmission, 0 volume and 8 transparent. glass artifacts

Here is how my bottle looked when modelling it in maya.

picture of bottle in maya

Edit1: added blender file link

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    $\begingroup$ to me it looks like the reflection of the grey backround, no? $\endgroup$
    – moonboots
    Oct 26, 2022 at 10:49
  • $\begingroup$ @moonboots if i remove the background theyre still there gyazo.com/27308cd11661ba68c385549b58c48a4a $\endgroup$ Oct 26, 2022 at 10:50
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    $\begingroup$ That's how it should look isn't it? You're looking through the thickness of the bottle glass in that area and that's what I'd expect ot see. Try it with a real glass bottle and compare the two. $\endgroup$
    – John Eason
    Oct 26, 2022 at 10:56
  • $\begingroup$ I notice the screenshot I added to the post doesn't make it look as bad as other angles do. I don't think it's supposed to be this "spotty" and uneven. gyazo.com/7638ca7c0172e66f92a4d85e7d9d3185 $\endgroup$ Oct 26, 2022 at 11:05
  • $\begingroup$ maybe give a Subdivision Surface modifier to your bottle? (with a Subdivision level of 2) $\endgroup$
    – moonboots
    Oct 26, 2022 at 11:19

2 Answers 2

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In my comments I mentioned the Transparent bounces, but they are more important for Fluid simulations with liquids or smoke. For glass-like materials there is something much more important, the Glossy bounuces. Of course always depending on the geometry, there can be many reflection bounces inside glass objects so that the default Glossy bounces value of 2 is almost always too low.

As said before, depending on the geometry you can get quite different results and sometimes a value of 8 is sufficient, whereas other times even with 64 you can still see changes.

I would always suggest at least 16, better are 32. If you don't have a scene filled with hundreds of glass objects even the influence on the render times isn't too strong. Just note that other than the independent Transparent bounces, the Glossy bounces are limited by the Total amount of bounces. Setting them high doesn't matter much if the total bounces are lower.

Here are comparison images with your bottle, you can see there the changes are very subtle and 8 bounces seem to be enough to make it look good:

bottle

Whereas in the images below, the slightly more complex geometry of the wine glass leads to more internal reflections on glossy surfaces and so there is still a very noticeable change between 16 and 32 bounces.

wine glass

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Turns out what I thought were artifacts are actually how a bottle would look like under similar lighting, it's just that the bottle wasnt subdivided enough. Subdividing made the "artifacts" look less spotty and made it look good. Adding an HDRI also made the reflections look a lot better.

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  • $\begingroup$ Sorry when I talked about the Transparent bounces earlier, what I actually meant was the Glossy bounces. I've prepared an answer just as comparison on how they affect the appearance of dark areas in glass. $\endgroup$ Oct 26, 2022 at 14:46

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