Patina!! Thats easy, well not easy easy but much easier than a perfect glossy paint job. The best look I've seen is to put a coat of light gray down then some red primer then a couple of different colors ie burgandy/green/red or whatever you want. Spray the last color the color you want the car to be, then start to rub it with a scotch brite pad paying particular attention to the high crown areas and heavily used or handled areas, such as the door tops and the crowns of the fenders, fender lips etc. anywhere that the paint would normally wear thin. Rub it thru the various coats of paint to give it the painted several times before look. The light gray will give a bare metal look while the red primer will give a rusty look thats appearing to be on top of the bare metal, the other coats will give it the worn look. When you get the look you want you can rub it out and bring a semi glossy dull shine to the whole works. I saw this done on a 34 Ford Roadster and it looked really good ( if you like that look, and I do ) Just take your time and have fun. The nice part is you can't really mess it up. I'm going to do my 29 this spring when the weather warms up a little.