Complex Fresnel vs Diffuse Color

[FrostKiwi]

Hey,
I heavily use (like many others here) Siger's Complex Fresnel for realistic Metals.
Metals are ment to have 0 RGB Diffuse, unless you want rust and grime mapped over it.

However, due to how Complex Fresnel works, it reveals the diffuse influence at certain angles, meaning now Diffuse Color actually does influence how the metal looks. Make it white, its brighter, 0 RGB and its darker.

How is it meant to be properly used?
0 RGB like always?
1 RGB to prevent energy being swollen artifacts?
Default Grey?

[maru]

I would say 0.
You use 0 for most metals even though IOR is not always very high - so this simply darkens the reflections. Same should apply here.

[FrostKiwi]

You use 0 for most metals even though IOR is not always very high

Makes me wonder, isn't IOR 999 the correct way to create metals?
No fresnel on Metals (+scratches + rust, dirt and fingerprints) is how I have been doing them for the longest of times, until I switched to Complex Fresnel, and it always looked spot on.

From your words I take it "even though IOR is not always very high", that you use Metals with Fresnel, even without Complex Fresnel?

[Juraj]

Well the difference is sometimes so subtle that it doesn't matter if you use the artistic way of metal creation which is just color and no fresnel. But since not all metals have such a flat specular curve, clamping by using darker specular color isn't as good solution as clamping it by using lower "simple IOR".

Even though "simple IOR" above 2.4 +/- is nonsense, the visual difference is again often negligible that it doesn't matter if you use that instead of ComplexFresnel or manual curve.

I use Complex Fresnel only in cases where I really want the "exact copy" of that material, like 24 carat gold, with the correct curve and hue. Otherwise there is no reason to be limited by such precise tool.

In your original question, answer is 0 diffuse anyway.