I got an email from a reader asking me how I did my chipped metal look on the Master of the Ravenwing.
I also used this technique shown in the Stompa yesterday. It's super easy. Simply take a piece of foam, for small models use a bit of foam that comes in a blister, for bigger ones you can use a bit of foam from a transport pluck-n-pull or whatever they call them.
Tear it at an angle. You want it to be a bit jagged but not too much or it will be splotchy. Test it out on a piece of paper or something first. Then, just dip it in your paint starting with Boltgun Metal. Wipe it off on the paint pot so that you don't have too much on the foam. Then dab it on the edges where metal is likely to chip. Be sure to rotate and move the foam in different directions or else all the chipping will have the same pattern. When you're done dab a bit with Chainmail, then a final dabbing of Mithril Silver (each one uses progressively less paint just like a highlight).
By the way, once the paint dries on the foam if you want to reuse it you'll have to tear it anew. The dried paint drastically affects its absorption and texture.
You can also do rust with this technique but that's already been covered by many others. I have yet to decide which I prefer but once I figure it out I'll be sure to post about it.