On 2021-11-24 11:14 PM (-4), Cousin Ricky wrote:
> It has become conventional wisdom around here, perhaps started by
> clipka, that metallic finishes should have zero ambient, and Alain has
> been carrying that banner ever since.  [...]
> 
> [snip]
> 
> However, I have examined less shiny metallic surfaces, and they do
> reveal faint cast shadows--the duller the surface, the more prominent
> the shadow.  This implies the real-life equivalent of a 'diffuse'
> component to these metals, and I do not see how a texture can have a
> diffuse component without picking up diffuse environmental light--i.e.,
> a non-zero ambient.

Since clipka has been posting about metallic finishes, over the years I
have been increasing the specular reflection and decreasing the diffuse
& ambient in my metallic textures.  This can be seen longitudally in
some of my Object Collection modules.  I am reconsidering the
AndroidRobot finish, though, for whenever Google next revises the robot;
I think the robot looks better semi-metallic.

For most metal surfaces, I'm finding this a good finish:

  finish
  { reflection { 0.9 metallic }
    diffuse 0.05
    ambient 0.05 * whatever_your_general_scene_ambient
    emission 0 // Suppresses 3.8's high ambient warning
    specular albedo 1 metallic
    roughness 0.0001 // or higher
  }

For polished surfaces:

  finish
  { reflection { 1 metallic }
    diffuse 0
    ambient 0
    specular albedo 1 metallic
    roughness 0.0001 // or lower
  }

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