Hello!
Is there a way to reduce, or have control over, internal reflections of a glass object? I’ve tried some solutions offered here. None of them had the desired effect so far.
This is my render and I don’t like those bizarre reflections of the cube on the inside of the dome.
These modifiers are on the glass dome:
And this is my node setup:
All suggestions welcome! 
First of all, glass produce shadow. The isShadowRay (or transparent color) needs to be fresnelled in some way.
Also, you could setup two different glass shaders manually - it’s basically fresnel mixing refraction and glossy - and then mixing them together using geometry/backfacing. On the backfacing one, you could turn down the reflection or even replace it with a transparency. Using transparency for glass, you may want to use inverted IOR for backfacing fresnel (has been shown here many times before).
Might want to check if the glowy material can be shader mixed with a transparency shader given a ray depth check.
Thanks CarlG, going to try that!
I’ve tried some more solutions offered on this forum (most of them by you) and I tried to come up with a node setup myself with the info you gave above. Nothing seem to remove or reduce those internal reflections. The glowing material is pure compositor btw and doesn’t need to be there. It’s just a place holder object for now.
Maybe it’s possible to put the glass dome on a separate render layer and combining them later? Or is this just a unwieldy noob solution?
then may be try Yafaray or Lux render
they got better Glass rendering then Cycles !
happy cl
Add a new material to the object, and make it a plain Transparent BSDF. Then in the Solidify modifier, change the Material Index Offset to 1. This will make the extra geometry created by the modifier use the next material in the stack. This should make the interior faces transparent and not cause reflections.
Thanks for that suggestion! I’ll look into it.
Thank you, this is very interesting!
I just tried it and it made the glass dome looking like it was massive glass (like filled with water). Maybe I’m missing a step?
Nah my bad. Try with a Refraction shader instead. I forgot there needs to be refraction on the exit face to correct the total refraction.
Well, I should have my eyes checked for not noticing your solidify - I thought that was what you were after, in which case this is what I came up with:
Inside reflection strength can be controlled with glossy color. If you don’t like the loss of energy, hook up the pure transparency instead. I’ll see if I can come up with something with a solidify modifier.
If all fails, you can always render twice; one full with cube reflection visible and one region with cube reflections turned off.
Adding a solidify to the example above (the bottom is closed off), I got some bizarre results; I couldn’t get correct normals, and when I applied it and fixed it, I had to take out the bottom. Having two separate bodies with inside normals pointing inwards suddenly wouldn’t work for me. Something else was whacked too, but I’ve never seen this before.
After I fixed the object and made it a proper lid, the “bizarre reflections” fixed themselves for me, and I ended up using just a normal glass shader and the fake shadow trick I use above.
I still have reflections, but they look natural and not completely on speed.
Wow, thanks CarlG! I will try this tonight 
[EDIT: It actually worked pretty well! Only needs some finetuning I think. Thanks again, man! 
]
I gave it another try. If your inside cube has a massive emissive strength (maybe in order to trigger glow), the fresnel equation will never drop enough - meaning the darkest area at facing angles will be bright enough to cause reflections (and mine is even worse because I use 1.65 rather than 1.45 for IOR, becoming more brilliant).
Here is a setup which allows you to control reflections at facing angles, as well as on backfaces (if you want to reduce double reflections). As always, use nodewrangler addon to preview what happens at the nodes. The green colored reflection is a reflection coloration that will happen on corrective glasses with anti reflective coating, I’m not sure if display stands would use this. But this is about getting control over the result while staying reasonable, not physical correctness. Shadows as before, fresnel based. Note that my emissive cube is of strength 25 and still reflections are under control (with IOR 1.65). If you replace the bottom shader mix input with the regular glass shader, notice how much more reflections it will have. I’m only affecting facing angles, at grazing angles reflections will be normal for glass of that IOR.
The two rightmost capsules are modelled correctly and cause no issues. The left one has bottom normals flipped the wrong way by force, also looks normal. The leftmost has a “unify normals” command, causing the two to accidentally point in the same direction, obviously rendering with huge issues. Not sure what caused my problems yesterday, maybe some normals were out of whack after all (when I thought geometry was ok).
I’m not sure it’s “correct” - whatever that may be in this case, but this is the setup:
Also note that rendering concave reflective surfaces can cause issues, like curved glass magnifying “erroneous” pixels that would normally be invisible (like a LED/LCD pixel mask - trust me :)).
