How do major studios fake the effect of "wear & tear" on the edges of guns and other things? I've always wondered this, but today it got to the point where I figured, why not just ask you guys. I"ve tried painting a greyscale mask, where the edges show a rough concretelike texture (Painted white and use lerp in ue4) but for some reason I feel like There is something im missing. Then, today I noticed sometihng playing BO3 - the edges seemed to have some more specularity on guns. Is this my answer? What process would you go through to show roughed edges? What goes into that effect?
Certainly when there is some kind of 'finish' worn off of a surface the albedo/diffuse texture changes, but what is also important is, as you note, the specular highlight as well as any glossiness or reflectivity. This is normally done with a grey-scale texture used as a mask to make the worn off sections look matte while the pristine areas remain glossy.
Edge effects are generally produced by using multiple surface materials (texture sets) and blending between them with hand-painted or generated edge textures. Note that these materials only exist in the artist's workflow, as they're rendered to a single set of textures for the game.
Textures that may contain edge information are curvature maps and ambient occlusion maps.
You can see how it's often done by artists in this video: https://www.youtube.com/watch?v=4fCF5HPc5_c