Just as a very rough guide, consider looking at those weapons I reskinned from Mackie's collection, to see the techniques for edge highlighting and using AO (which is a concept, not necessarily a software thing; I use Meshlab for AO burns, but only as a starting point for most things); basically, getting the metal look right is like Barf says, and I can affirm that he certainly knows what he's talking about.
That guide to hard-surface painting is extremely useful as a guide towards concepts and technique and well worth reading. I use a similar technique, with a few wrinkles here and there to add more depth to the colors in metals and handle some specific issues, but basically I am following Morrel's guide, and it's very easy to become proficient at speed-painting metallic surfaces once you know the system.
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