Problem understanding how to UV unwrap for bump and color material

Question

I'm pretty new to Blender and I'm using Blender 2.82, but my questions are fairly generic to the recent versions and revolve around getting a better understanding of how the UV Editor works. I've read through the documentation on UV Unwrapping and the UV Editor, but I'm unclear on the following. I'm trying to understand the process to use in order to UV unwrap for both a bump map texture and a color material using different images and different faces. I have a grayscale image for the bump map and a color image for the actual coloring of the mesh. Only a few faces need the bump map but the whole model will need the colored material. First, when using UV unwrap, do I always need to use the exact same faces? That is, can I uv unwrap a few faces for a bump map for only those faces and then uv unwrap those same faces along with all the others when I want to fit my colored material onto the mesh?

Second, when I UV unwrap for the bump map, I load the bump image into the UV editor, and I can get that matching on the mesh correctly, but when I go back to the uv editor to work on the colored material, the bump image is still there, and when I change it to the colored image, the bump texturing on the mesh disappears. So it seems like I can do one or the other but not both. I imagine there's a way to do both, but I just can't figure out how to do it. Hopefully all that makes sense.

Thanks for your help.

Answer 1

You can add up to 8 UVMaps in the Object Data Properties panel and use them independently in the Shader Editor. As you can read in the manual, each UVMap contains every face of the model, so if you wont unwrap any of them they will be at the bottom left corner in the UV Editor, so those whole faces will get the value of the bottom left pixel of the texture image. So I don't think this would be the optimal way for you. May be it would be better if you create a mask for the bump map.