wish i could learn to do that i have been colecting all the gear ie airbrushes videos powders and alike but yet to try them on anything 
maybe this summer
The nice thing about dry brushing is you do not need a lot of gear to do it. Just a brush and the surface you want to paint.
The trick is to get paint on the brush and then wipe it off so that the brush is just about dry - hence the term. Drag the brush across the surface allowing the brush hairs to catch the surface and leave light paint marks on it. That's the technicque - get an old brush, a piece of card board and a paper towel and give it a whirl. Try wiping more paint off and leaving more on, try more pressure and less.
Once you have tried the technique and got used to using it, the ways you can use it come thick and fast.
1. Highlighting
a) edges - dry brush edges in a lighter tone to highlight them.
b) surfaces - dry brush in a circular pattern to highlight the centre of a panel.
c) a quick dry brush on a figure will highlight clothing/uniforms to save work on bulk painting.
2. Weathering
a) mud/dust - use earth tones to add dirt and dust to a model
b) wear and tear - use a silver colour to show wear on edges and steps and where people have walked on painted surfaces.
c) rust - stipple first, then dry brush in successively lighter oranges to get rust on un-painted surfaces.
d) waterline - mask off the waterline and then dry brush the under hull with dirty colours to show algae and rust.
