Double reflection Glass problem

Hi, I’m trying to get out from a problem with Glass without success.
Here it’s 3 different files, the 3rd one is just made only on purpose to test it again, but still…
The problems are these double reflections.
I’ve read this same problem here: Double Reflection Issue but in my case it doesn’t work. I tried to use also only a Solidify modifier but no difference… I tried to make the glass using the Principled shader only, no difference… At this point I suppose it’s a normal effect of the glass shader, so how do you all manage it?

I can’t simply set the back side as transparent because the internal side is the one with the drops etc… And I didn’t know that it was the usual workflow actually. (I use Blender 2.79) I mean I’d expect that it’s included in the shader, no?

Normals are outward and consistent, surfaces are not double-sided, the mesh is “manifold”, so without holes.


nodes, simple

But I get the same also with other configurations

Hi @dinne7,

is this the effect you’re after, coloured splats on the inside of the glass?:


I’ve used two texture maps in this material ( the ‘splatter_mask’ is a pure black/white version of the ‘splatter_colour’ version - to act as an alpha mask, you could use a genuine alpha channel if the image format has one - jpg’s don’t).

The glass object has been unwrapped and is a full one surface mesh.

If you want this Blend file let me know.


A simple empty glass will produce these double (some times more are visible) reflections. It’s phisics.
But when the substance from the other side of the glass is not Air/Vacuum, the IOR changes, and it can minimize the inner reflection if the substance has a similar or greater IOR than the glass IOR; or it can maximize the inner reflection up to the total_internal_reflection, if glass IOR is greater than substance IOR…

Solution is to carefully map backfacing IOR values to match their difference with the outside medium’s IOR.

It’s got a double-reflection because it should have. Pardon the rather finger-smudged and grubby glass in the attached image. The bright reflection is a single rectangular bright light source. You can see that it is doubled. That combined with a suitable IOR is the way it should look.


Thanks to all, but your reply is the most useful because I never noticed it in real life. I don’t see it in the glass in real life but actually maybe it’s just because I never seen it on an “enough thick” glass…
I played a bit with IOR but I don’t get any difference, also combining them with various inputs in the Fac… Well then I’ll just think that I’ll make my glass as much thin as possible… For now.
Now I go to observe all the glass objects I have in the house ahah, thanks!

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I wasn’t 100% sure until I dug out that Mason jar glass and set up a light and took some photos. It’s roughly 3mm thick at least at the top. Following that I liked the shape of it so much I spent a while making one in Blender :slight_smile:

I like it. The roughness variation might do with toning down. The embossed shape it too sharp. The fingerprint is too clean and needs smeared or smudged a bit and the green effect is a bit overcooked. Too bad I closed the Substance Painter project without saving :frowning:

Oh well. I have a mason jar glass model I can use for something in future,

I was looking at the real glass again just now. I have some wee cheap LED lights that I bought to use for a 3D material scanner project. The LEDs at the front have tracing paper taped over them to diffuse the light. It gives me a bright rectangular light source. I think what’s happening is that the secondary reflection is light that has made it all the way through the piece of glass nearest the viewer and bounced off the far inside of the glass and reflected back to the inner side of the glass facing the light. That would obviously be affected by any objects or liquid within the glass. The larger of the double reflections I see is, well, larger, but also dimmer. I guess that one is the secondary reflection.

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Well, there’s me completely mis-understanding the problem - but sorted by John :slight_smile:
It is possible to do this in blender, but the glass does have to be quite thick to see it, which naturally causes the refraction distortions to be excessive:



The jar is amazing btw. And well you given me an idea, because you’ve all this irregularity, that is also normal for a glass object, while mine is just too perfect, too smooth… Maybe by adding irregularities I can mitigate the double reflections, yes… I made it much more thin now and I’m much more satisfied, but yes I’ll try by adding irregularities too!

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But, why are you using the Backface input to choose between 2 perfectly equal Glass shaders?

You’re quite right, it’s totally unnecessary, doh!
[ though of course that means by default you get double reflections - if the glass is thick enough to show it.]

maybe I should just shut up on this post . . . :dash:

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I have spent wayyyy to much time messing about with getting glass right in blender, so will save you some time… use the shader from the free Node Variety pack.

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