Mix black with either dawnstone and highlight up in layers until you use straight dawnstone, or do the same thing with boltgun metal.

Check out this mini by reaper for an example of the black and grey method


http://www.reapermini.com/FigureFinder#detail/60118

That looks really good. Do you mix them together on like a plate, or just on the mini? And slowly add more Dawnstone to the mix to make it lighter?

Yes, I always use a pallet. Once the mini is primed put the first layer of color down, your base coat. I usually start with a 1:1 ratio of black:dawnstone. Once this dries add another dab of dawnstone (add a drop of water) then apply another layer to the mini leaving some of your base coat exposed in the recesses. Add another dab of Dawnstone to your mix and another drop of water. Apply your 1:3 mix leaving a little bit of each successive layer showing. The last layer you apply should be either straight up dawnstone, or dawnstone with a tiny-tiny bit of black. Remember that each successive layer added should leave some of the previous layer exposed, so you will be covering less and less of the mini each time.

The drop of water added with each drop of color helps with blending as it will make each layer less opaque. If you find that once you are finished and you don't like the look you can try again, or add an layer of blackwash over the entire armored area. This blends the colors a bit more while tinting them a bit darker.

In fact that is a "short cut" method you might try. Paint on your black/dawnstone base coat, add your dawnstone highlights (don't worry about blending) then edge the plates of armor with administrator grey and finally once everything is dry add a layer of blackwash to smooth everything out. I used to paint flesh that way. Basecoat, highlight, layer of wash to blend. It works alright.

Painting black armor isn't easy, but with time it will become easier.