I want to simulate exhaust stains on a airplane. Everybody told me about pastels. I do have some dark grey and black pastel chalk. Now what do i do with it?, Grind it up? and brush it one?, Its goes on after my gloss coat right?

I use airbrush to simulate exhaust fumes and things, but if you want to use pastel, make sure the surface is matt. to provide grips for the pastal chalks.

I use the edge of a #11 blade to "shave" the colors into the small round depressions in the Testors paint trays. Lids from take out Chinese food condiments (my favorite paint palettes) also work great for this. Use an old brush and lead the stays away from the exhaust stacks, keeping in mind airflow. As you drag your brush away, you'll get less chalk down, creating a very realistic fade pattern. As mentioned above, this works best on a matte surface and should be just about the last step in weathering, since the real life effect is being renewed everytime the engine fires up.

Should you then seal the pastel chalk in with a dullcoat?? What if you got oil pastels that look alot like chalk but arn't for your b-day?? Are they a waste of money?

If you're going to be handling the model a lot you might want to seal it, but this may affect the tone of the pastels.

Oil pastels are not good for this. You might want to take up flat art to use them up if can't return them for chalk pastels.

CRAP, i didn't think they would work. And I can't take them back without hurting somebody's feelings. What do u do when your models get covered with dust on the shelf if you don't seal in the pastels? Won't the chalk come right off with the dust?? Or is that how you super builders get such realistic looking weathering to your AFV's?? You let the model actually weather on the shelf??

Dust is the long-term enemy of your models. Best way to beat this enemy is to put the model in a dust-free environment. A glass "cage" is your best option...
Jan