Please excuse me if I get terminology wrong here; I'm still learning. I have a mesh that is a humanoid figure with metallic clothing. When I channel-unpacked one of the included textures, I found this:
In this image, the white areas correspond perfectly with the metallic areas, and the black areas correspond perfectly with the non-metallic areas. Up to this point, my process has been like this: I rename the material Human_body, for instance, and then I create a second material called Human_body_metal. I then go into Edit mode and select all the polygons that would correspond to the metallic areas, and then assign it to the Human_body_metal material. I would then edit that material, adding the original image textures to it but changing the Metallic, Specular, and Roughness settings to get the reflective value I want. This has two significant disadvantages: first, it's difficult and time-consuming and second, there isn't always a clear polygonal delineation between metallic and non-metallic zones.
Having discovered this black & white image map, however, it seems likely that I am supposed to use this as a kind of mask, a way to differentiate between the two zones (metallic and non-metallic) for the mesh. How can I do this?