Another option that is very popular is a "Sludge Wash." Essentually, it is acrylic paint thinned with water and dish soap. This was a feature article in FSM, specifically; November 2001, page 42, by Paul Boyer tittled, "Quick and Easy Weathering." I believe you can find on this site under Techniques:
http://www.finescale.com/fsm/default.aspx?c=a&id=294
I use this technique all the time for my models and it works great. What I do is similar, only I use Van Gogh artist acrylics:
1. After the model's color coats have been applied and are thoroughly cured, I airbrush a protective coat of Future all over the model.
2. I mix the color(s) I need for the shade of wash for the model
3. I add approx one eye-dropper full of water and mix it with the paint in an empty film canister.
4. I then add 1/2 half eye-dropper of dish soap and slowly stir the mix until well blended. *Note: Depending on how much dish soap you add, the consistancy will be thick or thin. I tend to mix mine on the thin side as a matter of preference.
5. With a soft paintbrush, I paint the wash over details, panel lines, landing gear, etc. The beauty of this technique is that, if you make a mistake, or don't like the color, the wash can be safely and completely removed with a damp napkin or cloth and try again.
6. After the wash has been left to dry for approx. 15 min., I use dampened Q-tips and small folded napkin squares, I wipe off the excess wash from around the selected panels, recesses, etc.
7. When I'm satisfied with how things are looking, I finish by airbrushing a sealing coat of gloss or flat (depending on what your project calls for.)
Give it a shot, you'll get a kick out of how easy it is! Good luck.
Greg Williams
Owner/ Manager
Modern Hobbies LLC
Indianapolis, IN.
IPMS #44084