I'm trying to achieve a basic clear glass material, but it always renders as "black" glass. I'm new to Blender, so I'm probably making a fairly simple mistake here.

Thanks for looking...enter image description here

  • 2
    $\begingroup$ Share the blend file here please blend-exchange.giantcowfilms.com there's a hundred things you could be doing wrong and we can't possibly list everything :) Make sure your transmission samples in Light Paths under the Render properties is higher than 0 (bump it up to 3-4 for now) $\endgroup$
    – Jun
    Commented Sep 14, 2017 at 11:16
  • $\begingroup$ Trying the file, at least 6 bumps maximum is needed to give a better result. $\endgroup$
    – m.ardito
    Commented Sep 14, 2017 at 11:50
  • $\begingroup$ Thank you, m.ardito. I was under the impression that my light paths were still at their default settings, but this can't have been the case. I need to spend a little time getting to understand them. $\endgroup$ Commented Sep 14, 2017 at 12:10

1 Answer 1


Render settings light bounces, you need to increase their count. You can increase the maximum and transmission only for glass other bounces are used in different cases.

Basically light paths or bounces indicate how many times the emitted ray will change direction (hit a surface and bounce of).

Minimum are least number of bounces / light paths emitted. This value should be pretty low for performance but shouldn't be 0. 1-2 works fine for most scenes.

Max bounces indicate maximum number of bounces. If diffuse bounces are set to 10 and Max is set to 5 the maximum will still be 5.

Transmission is for glass objects using ... Well transmission. That's exactly what you're looking for. Keep it high for such a scene.

Glossy light bounces are for reflections, you could also increase that one a bit as well.

Generally only the first 5 bounces change the image quite a lot, the further you go the less visual impact it'll have. Performance wise it scales weirdly, the first few bounces are the most complex for the program and the rest still slow it down just a lot less.

Just don't set your bounces all the way down to just 1 - 2, it usually looks bad. :)

  • $\begingroup$ Hi can you explain how to change light bounces thanks $\endgroup$ Commented Dec 13, 2018 at 1:50
  • $\begingroup$ If it's still needed, you do that under render settings in the properties window. The tab is called Light Paths and there you have light bounces settings. The more you set the slower it'll render but the more realistic the lighting will be, however there's a certain point of diminishing returns, I usually avoid using more than 16 bounces unless it's a product shot and render times don't matter. Glass and transparent objects may use a lot more if you get the dark edges on transparent or glass materials. $\endgroup$
    – Aras
    Commented Jul 18, 2019 at 15:10

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