IOR useless when Metalness 1?

[JonasNöll]

Hi there,

I noticed that in V-Ray 6 the IOR value doesn't seem to have any effect anymore when the Metalness is set to 1. Is that intentional?
In earlier V-Ray versions that was different, so just wondered if that's possibly a bug.
The metal material presets also have different values for the IOR setup but as said it doesn't matter if the ior is 1,01 or 50...

[hermit.crab]

Here is a summation of the discussion with the developers:
1. There is no bug, but rather a change in metalness behavior due to an introduction of a more accurate metallic fresnel calculation
2. The current behavior for metalness does not depend on the Reflection's IOR parameter, but rather the IOR is calculated internally from the base/reflection colors
3. We will document the changes soon.

[DougBowker]

Interesting... I hadn't noticed this because I tend to reuse known materials for the most part, and hardly ever just grab a "fresh" material and start from scratch. But when I did just now, sure enough the pre-baked VRay Steel or Chrome definitely is unaffected by IOR.

[vladimir_krastev]

Hi, thanks for contacting us. Please read this article - https://www.chaos.com/blog/understanding-metalness
In it there is this explanation regarding Metalness set to 1:

When switching to a metal material, which is done by making the Metalness value 1, the variables take on different meanings:

• Since there is no diffuse color in metals, the diffuse color becomes what is known as the base color — or albedo color.
• The Reflection should be set to white so as to get the proper reflectivity and preservation of energy; without this, the glancing angle will never be 100% reflective — which it should be.
• How much that reflection is blended in is still controlled by the same IOR value of the Fresnel effect; you'll notice this now has a very subtle effect as the entire material is basically reflective — it’s as if you are blending two different reflections together.
• Glossiness controls how shiny it is; however, if you use a roughness map instead (such as what Substance does), you can switch your V-Ray material to use roughness — which is the inverse of glossiness.

[JonasNöll]

Hi,

my question is more that it has obviously been changed. So now there is literally 0 effect anymore no matter if the IOR is 0,1 or 200. It looks absolutely identical.
In V-Ray 5 changing the IOR had a very drastic effect, even the metalness was set to 1. As you can see in this video here there is a very noticable change when adjusting the IOR: https://www.youtube.com/watch?v=3KQy...nel=JonasNoell
That is in V-Ray 5. So it apparently has been changed and/or is not working the same anymore like it did before.

[dlparisi]

Hi,

my question is more that it has obviously been changed. So now there is literally 0 effect anymore no matter if the IOR is 0,1 or 200. It looks absolutely identical.
In V-Ray 5 changing the IOR had a very drastic effect, even the metalness was set to 1. As you can see in this video here there is a very noticable change when adjusting the IOR: https://www.youtube.com/watch?v=3KQy...nel=JonasNoell
That is in V-Ray 5. So it apparently has been changed and/or is not working the same anymore like it did before.

Additionally, some of the metal materials from Cosmos have metalness at 1 and a non-default IOR set (see Silver Blurry #0 for example). I've no idea if they are render as intended. Maybe just an oversight though.

[hermit.crab]

Just so you know, we are aware of the different behavior. I'll write back with more information about why is that so.

[hermit.crab]

Here is a summation of the discussion with the developers:
1. There is no bug, but rather a change in metalness behavior due to an introduction of a more accurate metallic fresnel calculation
2. The current behavior for metalness does not depend on the Reflection's IOR parameter, but rather the IOR is calculated internally from the base/reflection colors
3. We will document the changes soon.

[JonasNöll]

Hi, thanks for clarifying! So if I understand correctly then:

- There is now no way to control the transition between the minimum reflection (diffuse slot) and maximum reflection (reflection slot) anymore. The transition is fixed and the same for all metallic materials.
- The IOR values for all metallic materials in all the cosmos materials and material presets is just cosmetic and has no effect anymore whatsoever

Seems like a questionable choice to me, but if you say it's not a bug and intentional then I guess we have to accept it as it is for now

[Joelaff]

Yeah, for creative control (rather than scientific "correctness" control, which I can rarely convince our clients of) it would be nice to be able to control the falloff manually. I suppose you can still put a falloff map into the reflectivity, though.

[kosso_olli]

This indeed sounds questionable.

[hermit.crab]

The transition is fixed and the same for all metallic materials.

The transition is calculated internally for each metallic shader and is based on the diffuse/reflection.

The IOR values for all metallic materials in all the cosmos materials and material presets is just cosmetic and has no effect anymore whatsoever

The values there were set prior to the change. But, at the moment, yes.

[jackieteh]

So how can we control the reflection amount now since IOR is not working?

[^Lele^]

The metalness workflow is as physically accurate as it needs to be.
Metals have an inherent reflection behaviour, if you need to tweak that, you will have to do it as in the real world counterpart: what is in fact changing the metal's reflection?
It could be grime on top (so, a layered shader with the grime one), it could be oxydation (so the metal is an oxyde of the source one), is it the scratches on the surface (and so one will need a normal map for those), and so on.
The non-metallic workflow is still available if you prefer to go about it the old way, guessing what the properties ought to be, and tweaking those to one's preference.

[jackieteh]

The metalness workflow is as physically accurate as it needs to be.
Metals have an inherent reflection behaviour, if you need to tweak that, you will have to do it as in the real world counterpart: what is in fact changing the metal's reflection?
It could be grime on top (so, a layered shader with the grime one), it could be oxydation (so the metal is an oxyde of the source one), is it the scratches on the surface (and so one will need a normal map for those), and so on.
The non-metallic workflow is still available if you prefer to go about it the old way, guessing what the properties ought to be, and tweaking those to one's preference.

Remove the IOR control when we choose metalness, this way will make less confuse...??

[hermit.crab]

Remove the IOR control when we choose metalness, this way will make less confuse...??

It will be greyed out.