Correct setup for dialectic materials in PBR metalness/roughness workflow

[second-ich]

Hello,
I just read this article about the metalness PBR workflow in Vray:
https://www.chaos.com/blog/understanding-metalness

It says that conductive materials should always have a reflection value of pure white and only roughness is used to make them less shiny. Is this also true for dielectric materials?

Thank You

[hermit.crab]

No. By dielectric understand all non-metal materials. Both glass and paper are dielectric, but their reflectivity may be drastically different.

[second-ich]

Ok, because according to the PBR principle paper and glass should have the same reflectivity but different roughness.
Is there a table to look up physically correct reflectivity values for Vray?

[hermit.crab]

Quoting the article you linked and bolding the important bits:

Your PBR workflow

Now that we have established that you should consider metalness more as an on or off state, let's look at how to make the material work. When making a dielectric material, diffuse color controls the Lambertian part of the shading and the reflection is controlled by several variables: Reflection color as a multiplier of the overall reflection; IOR for the proportion of reflectivity on the forward-facing normals, versus the glancing normals (also known as the Fresnel); and Glossiness (or its inverse roughness) for the overall amount of scattering, depending on the BRDF model you select.

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.

As for your second question - we do not provide such a table, however, the VRayMtl's presets are a good start.

[second-ich]

Are there any plans for a complete PBR workflow? This would make it easy to achieve photorealistic results.

[sirio76]

Achieving photorealistic results have nothing to do with using PBR workflow it is just a fancy convention but artists where able to get great/photorealistic results ages before the PBR workflow was “invented”.

[second-ich]

Achieving photorealistic results have nothing to do with using PBR workflow it is just a fancy convention but artists where able to get great/photorealistic results ages before the PBR workflow was “invented”.

I know. But it makes it easier since there are less parameter you have to control.

[demonslayer]

Curious to know why the Plastic and Chocolate preset already comes with a Value of 120 or 113 which is way above the (maximum) value75 sRGB that the PBR Guide PT2 states?

[hermit.crab]

Curious to know why the Plastic and Chocolate preset already comes with a Value of 120 or 113 which is way above the (maximum) value75 sRGB that the PBR Guide PT2 states?

I don't think the V-Ray shader presets are meant to be PBR (even though some of them are). I mentioned them solely as a starting point to create your own shaders. Also, there's a paragraph with additional information for the shaders you mentioned in the docs.