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In a PBR metal/roughness workflow, I know that all dielectrics are hard-coded to have 4% reflectivity at F0, and metals have a much wider range of 70%-100% reflectivity. It's important to use the correct reflectance values, but if I'm using images, then don't they already have the correct values? It would seem to me that creating procedural metals would require using online charts to get the correct values. For example, if I want to create a gold sphere, the values are (1.0,.76,.33), and I would enter these values in the color swatch to get gold.

However, if I have an image texture of gold, I would simply plug that into the Base Color socket and not concern myself with the reflectance values since it's an image of what I'm trying to create. Am I correct?

I've poured over countless web pages and .pdf documents about PBR, and I've found nothing that explains this.

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    $\begingroup$ This is not how PBR work, your image doesn't carry any data regarding roughness, metalness, or specularity. The Base Color is exactly that, it's just a color. Try plugin your image in a diffuse shader and that into the output node, that what the base color of the principled BSDF is. Look up PBR workflow, specifically what's a roughness map and a normal map as with the base color this are the 3 most important channels in a PBR workflow. $\endgroup$ – Arthur Blaquart Nov 13 '19 at 16:56
  • $\begingroup$ Okay, I got it now. I don't know why I was assuming that the image would "know" whether the material is metal or non-metal. My brain must not have been functioning lol. All the image knows is the color of each pixel, and the shader (more specifically, the Metallic slider) is used to give the image metallic properties, and the base color has the color of those metallic properties. It all makes sense now. Thanks! $\endgroup$ – MeshHead Nov 13 '19 at 17:50
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The base color is not affecting whether the material is dielectric or metallic. In the Principled BSDF you have to set Metallic to 1.0 for a fully metallic material. The manual explains metallic in the following way:

Metallic

Blends between a non-metallic and metallic material model. A value of 1.0 gives a fully specular reflection tinted with the base color, without diffuse reflection or transmission. At 0.0 the material consists of a diffuse or transmissive base layer, with a specular reflection layer on top.

If you were to connect an albedo texture of a gold material or assign a color to the Base Color socket of the Principle BSDF while Metallic is set to 0, you would get a non-metallic material that could look like the following image.

Non-metallic

Once you set Metallic to 1.0 it will look like a golden material.

Metallic

More examples of how the different properties affect the material can be found in the manual.

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