I'm going through BlenderGuru's tutorial and he's using Principled BSDF as a glass material and Cycles as the render engine. The cup by itself looks fine, so does the plate, but if you look through the cup at the plate, it's all weird and kinda dark. Same if you look through one cup at another cup.

I've set the Base colour of both the cup and plate's material to pure white (it's the same material anyway), same with Surface Colour. Roughness is set to 0, IOR is 1.5 and in Render Properties Light Paths>Max Bounces Total, Transparency and Transmissions are all set to 8 (I increased these to 12 to no avail). I also turned on Reflective Caustics and Refractive Caustics.

The last image is what BlenderGuru's realtime render looks like. No weird transparency issues there.

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Anything else I can do?



1 Answer 1

  1. Add a lip to the cup. This will help guide the direction of refraction rays. Most cups have a rim, and the glass shader is physically-based, so you're probably going to get weird results if you deviate from the real world.

  2. Increase glossy bounces to something dramatically higher, like 64-128. This will help ensure enough glossy (reflection) bounces hit the rim of your cup. Also up transmission bounces to something like 64. This will help stop refraction rays from terminating too early.

  3. Add an HDRI, more lights, and/or simply add a box or some other objects surrounding your cup. The environment is mostly causing this. At the moment, your world color is just a flat color, and you only have a small pink plane that the cup rests on. There's very litle for light to reflect off of, so you get too much refraction where there should be reflection.

See: Excessive refraction at glancing angles with glass and/or fresnel nodes?

This is how it looks when I upped glossy bounces to 128 and transmission bounces to 64. I think it's significantly improved already. It's not perfect though, and you can further improve the realism following my other steps. Most important is an HDRI or some other more realistic environment instead of endless empty space.

enter image description here

  • $\begingroup$ Thanks, Joe! I uploaded the .blend file just now. Thank you for your help! The thing is, I have followed the tutorial pretty closely, I'd say. I think the cup already has a rim, but it is possible I might've messed up somewhere, I really cannot tell, I'm afraid. I did have a hard time making the handle. Not sure if in the process I inadvertently deviated from the tutorial... I tried increasing the glossy bounces to 128 and it made no difference. :/ The weird thing is, in BlenderGuru's tutorial, he has the same exact setup, just a light, camera, cup, plate and the flat pink plane... $\endgroup$
    – hexoral333
    Jul 22, 2020 at 17:37
  • $\begingroup$ @hexoral333 Thanks for sharing your file. I updated my answer with more information, a screenshot, and a new download link to your file. You forgot to change the "total" bounces in the light bounces area. So even though you had 128 on glossy, it was still set to 8 total, so it didn't work. $\endgroup$
    – Joe
    Jul 22, 2020 at 19:16
  • $\begingroup$ Thanks, Joe! Your render looks definitely better, but it still looks a bit odd. The cup definitely has a rim at the top, just like in the tutorial and frankly, I've closely copied everything else BlenderGuru was doing, yet he doesn't have this problem. He has the same pink plane, no HDRI and a single light in the scene. Do you think this might be due to differences in the versions of Blender? I'm using 2.83, but I think he was using 2.80 or 2.81. At any rate, later in the tutorial he will add more objects to the scene and improve the lighting. Do you think that will fix this problem? $\endgroup$
    – hexoral333
    Jul 22, 2020 at 22:16
  • $\begingroup$ @hexoral333 That's because your point light has max bounces set at 4. That's extremely low. The default is 1024. Here is how the render looks when you turn up the max bounces of the point light to 1024 -> imgur.com/a/2td2qMq $\endgroup$
    – Joe
    Jul 23, 2020 at 4:18
  • $\begingroup$ OMG, yes, that's it! Thank you so much, Joe! I want to mark your answer as correct, but since it's just a comment, maybe you can add this last solution to the main post? $\endgroup$
    – hexoral333
    Jul 23, 2020 at 10:13

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