I've had some questions about how I'm currently doing my old/worn/rusty/dirty metals such as those on the orks and skeletons (I'll post some close ups of the effect on the skeletons soonish).  Here's what I do.

- All metal areas are blocked in with boltgun metal (over black primer)

- I give the metals a light chainmail drybrush. This is to create a highlite from beneath the washes that follow.

- This is the key step: all the metal is given a special wash. I say "special" because it's not 1 product, it's a mix I've created using a variety of things. The base of the mix is called "Kel's Magic Sauce" (currently called "Didi's Magic Ink") from the Warstore. To that I'm adding various Vallejo Gamecolor Inks: Sepia (lots of this), green, some yellow (not much, it's very strong), some brown.  I do this until it's "about right". That's the problem - I dont use specific measurements.  I just throw it in.  As with all washes, I'm careful to keep it from pooling. It tends to do a great job of "glazing" and filling in recesses without pooling, I suspect based on being a mix of wash and ink.

- after that I dapple/dab on (like, dots from the end of a somewhat flat old brush) Vallejo Dark Rust and Light Rust (basically, only in very small amounts)

- finally, Im using that MIG pigment (standard rust) and applying it very sparingly in recesses and other areas until things look "about right"

- depending on if I think it's needed or not I sometimes do a very light chainmail highlite to the larger areas or edge highlites

Thing is, it's not an exact science to apply, but these are the steps I'm using.

One thing that's awesome about this is I find "orange" metals like bronze, brass etc go on beautifully over top of the second stage wash.