I tried to flesh out your words from a previous comment about making it look like an unknown metal.
... layers upon digital layers of textures and gradients here, ... trial and error, choosing one, rejecting it, choosing another, over and over until it felt right, ... adding an element here, adding an element there, ... nope not enough yet, ... is it too much?, ... does it need more?, ... should I stop now?, ... you know the drill.