For this technique to work, the model must be ready painted and varnished to a completely flat finish. Matt surface is necessary for the pastel pigment to adhere. The process itself is straightforward. First, a piece of pastel chalk is ground to powder. The powder can then be picked up by a dry paintbrush or Q-tip, and gently smeared onto the surface of the model.
Pastels work best for simulating exhaust stains, gun powder residue, and dirt in general.
Drybrushing Drybrushing is a way to highlight raised details. A brush with slightly stiff bristles is dipped in paint, then brushed off onto a piece of paper towel or cardboard until it is nearly empty. The brush can be then lightly scrubbed over the raised detail you want to highlight. The sharp edges of the detail engraving will tend to scrape what little paint is left on the brush onto the detail. For drybrushing, you will normally require a lighter tone of the base paint your model.