Trying to move beyond "ordinary" metals...
My technique for painting white metals (silver, platinum, steel, etc...) is based on the ideas of a member of the Mini-Painter E-group. I can't think of his name for certain, but Dirk Stiller comes to mind ... my memory frequently fails me though, so I may be wrong, in any case I'll find out for sure and put in here when I know.
When I first started, when painting (white) metals, I would just do a black base, drybrush gunmetal, then highlight with chainmail, and finally a highlight with mithril silver (these are all GW paint names). While this method can certainly achieve a very nice effect it has limitations, primarily in that the transitions are not always very smooth between shades.
So recently, I began using an ink wash technique that can really make your white metals look great! The solution that I use is composed of 1 part black ink, 1 part blue ink, 1 part green ink, 1 part purple ink, and 3 parts 50/50 future floor wax/water mix. This should end up looking like a super deep greenish, very thin ink. It should have very little covering ability. We are going for a subtle effect here and smooth transitions. Feel free to experiment with different mixes. Really neat effects can be achieved and I'm only talking about the mix I use most often here. Once you try the technique, if you like it, I recommend mixing up a bottle of your favorite mix. This will save you a ton of time in the future.
To start with, base coat the metal area with black paint. Keep it thin to avoid obscuring detail. Next paint on your medium white metal color, GW chainmail in my case. Give the whole area a wash with the mix and allow this to dry. Now it's time to put some highlights on. Using your white metal highlight color (GW mithril silver for me) pick out the high points and details you want highlighted (you should be using SLIGHTLY thinned paint for this). Now the highlights are done and it's time to add some depth. Give the whole thing another wash of your mix and let it dry. Now using the same slightly thinned mithril silver as before, go back over your highlights, just adding a tiny bit of paint to the very highest areas. You should leave some of the mithril silver tinted with the ink wash showing.
After your last highlight step it's time to begin shading the metal. Think of the shape of the object(s) and the directions the surfaces are facing. Surfaces facing the ground should be darkest (along with very deeply recessed bits) and you can achieve a nice result by shading the point where surfaces at different angles come together. Surfaces that are perpendicular to the ground would reflect the horizon, so you can use a dark line for the horizon, a slightly lighter shade below it and a much lighter shade above it.
As an example think of a sword blade. Imagine it is held parallel to the ground, but with the blade at a slight angle (the flat does not face the ground directly). Because the blade is a diamond cross section you can see that two surfaces face the ground and two face the sky. By shading these appropriately you can achieve a very realistic look for the metal of the blade. Since the four surfaces are all at different angles I would shade each to a different degree and then retouch you final highlights if need be. Those surfaces aimed directly at the ground should be darkest and those aimed directly at your imaginary light source should be lightest.
Finally, you can experiment with tinting your mix to show the colors the metal would reflect, so the sword in the example above might have a more greenish tint to the bottom surfaces (facing the ground/grass) while the upper surfaces might be slightly blue (reflecting the sky).
Above all, experiment, try new things, and do what YOU feel looks good!!