TheBaron, not to go off on a tangent, but you brought up the pastel chalk.I've used it with varying success. The one thing about the chalk is the prep on it. Someone recently suggested picking up a cheap coffee grinder to make the powder. Have you heard of that? Seems like a pretty easy way to make up decent batches of the pastel powder. Especially if you do what I do & blend different chalk colors for dust or earth tones. I've never tried dullcote or hairspray to apply it. I've either applied it right after painting to the still slightly wet paint (works great for rust effects) or used a light ink wash & then dusted on the powder. the ink wash seems to do a good job holding it in place. The only drawback to that is the ink wash can obscure the base paint job if you're not carefull or don't want it to look to "dirty" and weathered.
The coffee grinder is an interesting idea, but I suspect it would end up looking more like a Three Stooges short than a workbench

I can't imagine needing that much powder at once, and while I can see laying up a supply and storing it ground, I've always gotten by on grinding what I need at the time. I just take the chalk stick and scrape along an edge, using the knife blade, depositing it into a cup on my palette. A couple of passes usually gives me enough. Then I blend it, like I would blend paints, or apply colors one at a time.
On the P-40, for example, for the engine exhaust staining, I started with the lightest color, which covered the largest area of the stain, brushed that on, then added each successively darker color, in a smaller and smaller area, until I hit black in the very center. I did the machine gun exhaust stains the same way, except with fewer colors (brown and black), and on a smaller area. For the wing and fuselage surfaces, I mixed on the palette a very light gray shade with white and black chalk, and brushed it on with a wide brush.
I've also used the chalk to make mud, by adding a drop or two of liquid soap, a drop or two of water, and stirring till mixed, then applying it to the model. The soap helped keep it from running, and I could use a lot, to look like mud clogged in the road wheels and tracks on a halftrack, or I could also add a drop more of water to thin it, take a little on the brush, and streak it to look like mud spattered on the fenders and sides of the vehicle. But I like how easy they are to handle.
I got an inexpensive (maybe $10?) set of earth tone chalks at an art supply store, but I think Michael's or AC Moore might sell them, too.
I have an airbrush, but I'm afraid to use it

One of my modeling goals for this year, though, is to overcome that fear, because of the things you can do with an airbrush.