Few "natural" metals exhibit significant diffuse reflection, as that requires subsurface penetration or a very rough surface, and it simply doesn't happen with polished metal.

Nevertheless, for purposes of fantasy materials, you can mix diffuse and specular reflections. Some examples in green here.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)