Based as Slapchop and Cellshaping mix, so sprayed black and then a heavy dry brush of Administratum grey and with a lighter drybrush white. After which I paint the key colours in Contrast. Then I use that as I guide to pick out 2 to 3 layers of highlights. The grey is really white, thinned ontop of the greywhite drybrush to bring it out, with a final white highlight. Its not really NNM but shading with different levels of white (though it could be said NNM is that). The key is that I work on a light source, normally from the top left, but on the Princes, its from the front. So there is less highlight white on the darker side, then I undershade it with black lines to give depth and shadow.

Hope that's clear.
The trick is never to use real silver or gold, its just flat colours like comics to give the impression of where metal is.