There’s several ways you can create a bump map. For this roborb model I used photo textures of grimy scratchy metal. The reason I choose this most of this time is convenience. We could paint anything by hand, but you have to be good at hand-painting and you have to be patient during that painting process. At least compared to simply loading a photo of the texture that mostly fits what you’re after.
But yes, you can easily lay out UV’s in Blender, take a UV snapshot image, open that image in Photoshop and paint a custom scratch/grime texture. That’s a fairly old-school way of texture painting but it’s still plenty viable. You can also paint directly on your model in Blender.
