dry brushing

All the above is excellent advice. My rule of thumb is, when you think you have taken enough paint off the brush, take off a little more (you can always add more. It's tougher to get it off once it's on). You'd be surprised how much paint a brush will hold. Pete

The only thing I would add is "easy does it" with a little patience. Its way to easy to leave too much paint on the brush or go over an area too many times. Do it a few times with very little paint will give you fine control over the effect.

Here is another often overlooked use of dry-brushing:

Feathering edges of brush painted finishes and camouflage patterns.

Many uses to it, the limitations are only defined by your imagination.

QUOTE: can this technique be used to say....simulate worn off paint?

Yes, that too.
But I think the main purpose is to highlight the edges and raised detail. In 1:1, they (edges, details) are highlighted naturally by the light. In small scale models, this effect is not present (because the objects are so small) and the shapes do not seem so well defined. Modeler must "help" this by
- applying dark wash (to represent shaded areas) and
- drybrushing with lighter tone of the basic color (to represent edges etc that stick out)
Other uses for drybrushing are also on large areas of models (airplane wings & fuselage, AFV exterior plates) for emphasizing different color tones within panels or applying various stains (fuel, oil, exhaust, gunsmoke stains) although for this other techniques can be used

can this technique be used to say....simulate worn off paint?

i have a tank with a mine plow and i might try this to show the teeth on the plow have been used and some of the paint had come off and shows "bare metal". like dry brushing some steel and rust on the teeth.

That is basicaly when you take a paint brush, dip it in the color you want, and then wipe most of the color off onto a bounty. (hence "dry" brush) Then you lightly move the brush acroos the area you want to dry brush, and slight residue of paint is left along the raised detail.