Exhaust stains

Alclad makes a really nice Smoke shade, too. Tamiya's seems to be warmer/browner, and Alclad's cooler/bluer. 

My exhaust technique depends on the plane. I'll usually use Smoke of one form or another as a base, then go over with pigments, slowly building it up with a small brush. I'm a big fan of Mig's Burnt Metal Blue. Adds a nice touch to the whole affair.

On my recently completed Spitfire, I went with grayer tones to match the references I had, and used an Aqualon Wisp brush to do the vertical streaking:

I use red brown overlayed with flat black. This is for the FW 190, which had pretty big exhaust streaks from the radial engine.

I don't recommend paint of any type..

I use soot for soot... Or charcoal and pastels...  I get far more control that way... Plus, the exhaust stains on blue-camouflaged aircraft call for more greys...

I was using my airbrush for exhaust stains until Tamiya released their weathering "compacs". Those are my sole tool for that now. Each comeswith a little applicator and I use a micro brush for any smaller or harder to reach spots that the kit supplied applicator wont do properly.

  Stikpusher, those look fantastic; just the right amount without overdoing it. I'm doing my current build with a small piece of sponge on tweezers and heavily diluted Tamiya smoke. So far, so good. I'm going to try those next.