I'm trying to model a textured and anodized aluminum material (think Apple MacBook). I'm using the Principled BSDF node because my end target is a glTF for display in the browser. Whatever I do, when setting metallic to 1, it always comes out black (both in Blender, and when rendering with three.js/WebGL in the browser).
I tried to duplicate some of the examples here, and I get the same result. I believe the issue is something to do with not having the correct light sources or scenes to reflect, but I've tried variations of environment maps and actual scenes with various types of lights, and I never get anything other than solid black/dark grey.