Glass Material: Raytracing Translucency?

No matter what I do. As soon as I fully Raytrace the Refraction / Transluceny … the Glass Material turns out to be black.

Here is a short 4k-Video that describes very clear the problem:

Does the teapot have an “inner” mesh? My guess is that the outer face is casting a shadow on the inner face. There’s also limitations mentioned in the Ray Tracing Supported Features in terms of translucent materials. These might have something to do with what you’re experiencing.

@BernhardRieder The more complete solution for translucency with realtime raytracing will be on UE4.23, you can go to GitHub and download the latest commit for the Rendering branch and build the engine for yourself and you will see your issue is probably gone, or wait for the preview 1 to be released in another 2 weeks approx.

Thanks for the info, appreciate that!

So that means, it’s just not working with the current release and I just have to wait until Unreal 4.23 will be out and that problem will be fixed?

Yes, it is not working with the current release. The realtime raytracing is in early access, meaning it is not complete, with features still being added, other features still being fixed aswel (translucency, landscapes and foliage), with optimizations being done at the denoisers too. Those many mentioned will be fixed in 4.23. There is still things that will only work properly “or” optimized in later releases (Niagara, multi-GPU, etc). If you can’t rebuild from source, you need to wait and check for the previews starting in 2 weeks or later when the 4.23 releases, add at least an entire month after 1st preview.

Hi Nilson!

Thanks for the info. I mean, 1 month until fully raytraced Refraction is working… that’s awesome. Hmm… sooo… as a workaround… and if you can’t or don’t want to use Raytracing for Refraction. What’s the workaround and current solution?

I mean… translucency kinda works, right?
Is it a different material that should fix that current problem?

Or is it something in the settings?

Anything I could make the glass look like real glass and get the effect without the Raytracing?

One question didn’t get resolved till today:
if you need a shell on a geometry, or if you don’t need one.

Offline Raytracers like Vray, Arnold, etc. all require a shell - meaning, a polygon that has two faces and normals are facing inside and outside.
I think it’s very important to know that as well, because the geometry preperation for all refractive objects needs to be correct before applying the material.

What are your thoughts on this?

Thanks a lot for all your input - you made my day!

I am not following up the changes in the Rendering module at the GitHub, but the changes are not just a material or settings, it is in fact the Rendering module being modified, meaning no workaround for now.

I might be wrong, but so far all points to no changes in materials to have the same glass appearance as in the rasterizing method. For glass to be like the real thing with refraction etc in real world, probably they will show up some better way to setup a material to have that. Unfortunately we will need to wait.

Hi Nilson!

appreciate it. I was running another quick test. In this Video I compare the Unreal Raytracer vs. the Vray Raytracer.

I followed the Unreal documentation to create a Glass Material with Refraction.
The result… unfortunately… does not work.

Watch here a short 4k Video with Audio Documentation, highlighting this major problem:

Following your messages:
Does this mean, that refraction just doesn’t work at all until the new Release of 4.23 is coming?

Source to the Unreal Documentation of the Glass Refraction Material.

That documentation you pointed out is currently the material setup for the rasterized method (UE4.21 and earlier) and so far that one works (sort of) for glass. My material setups I usually put a fresnel node going to Opacity and if the glass should show the inner side, I use double sided material, so I can fake thickness. More thickness to glass, above 1mm, would require a mesh like you described earlier, having an inner mesh with normals respecting the surface continuation from outside.

My expectation is that 4.23 with the adjustments in the translucency we can rely on the same material method used for rasterized or have anything extra in the settings to make it like the other renderers work such as VRay.

Is it possible to download somewhere a material/shader you mentioned, that works for refraction when using raytracing?
I am having the same issues… I can’t create get a glass material that works when using raytracing for the translucency.

The link is in the documentation as he stated here:, but it won’t work for all cases in Raytracing because the feature is under development, since the realtime raytracing feature is still in early access, and you can expect the next release to have the issue with translucency behaving as expected and also we will know if the feature will require material adjustments or if the way it is in the documentation will work out of the box.

I see. I guess all we can do for now is waiting. Thank you!

He there,
I’m on 4.23 and the problem is still there. can you confirm that ?

Not working yet, translucency is still work in progress in relation to realtime raytracing. Also, translucent materials won’t appear in reflections and the shadows from the meshes using them is solid black.

The IOR doesn’t seem correct to me either, it’s not changing at all when I adjust it.

Yeah, not being able to adjust the IOR is super annoying.

With the latest Release of 4.23 it’s working. I created a Video Tutorial for it. If you follow the steps, you should be able to get the same results shown in my video.

all details can be found here:

My Final Result:

My Video Tutorial:

I hope that helps - happy ray tracing!
cheers :slight_smile:

@BernhardRieder AFAIK you are still not able to see translucent materials reflected on other surfaces and those are also showing solid black shadows in reflections, so translucency still broken in several scenarios in 4.23.

the tutorial is informative. The glass material is really great with Ray Traced Translucency on, but the RT T Refraction is still off.
Cannot find nothing on how to properly use RTTR yet, specially geometries that are slightly more complex!!1136573952.jpg

do you have a model like that? I would like to run some more tests…