The salt technique I use sometimes, mostly in WW2 airplanes...japanese mostly!! is as follow:
I paint the base color I want to see in the "chiped effect", it could be silver,gray,red-brown or steel, then after is compleatly dry...usualy and in my experience 48 to72 hours...I wet with water with a soft medium paint brush the model areas I want to create the effect, sprinkle the salt in those areas, working in small areas/patches of the model surface, cleaning any unwanted salt particles from areas that will remain "unchiped". Then after the salt/water is dry, paint the top final color....via airbrush is the best since you can control the amount of air preassure and not blow off the salt particles...or if you need to use a spray paint bottle, do it at a distance, like spraying a mist coat. After the paint dry compleatly, take a old paint brush and begging to sweap/clean the salt one spot at the time, a 2000 grit sandpaper is also handy for final cleaning, but be very,very gentle in it's use. You should experiment in an old model kit body, like a car,plane or even a piece of plastic so you can get the feel of the salt/water/paint combination....but trust me is quite easy once you get the hang of it.
The you should have the chipped effect, you can finish it off with some chrome silver(work best for me in my humble opinion) very small and shoft chips using a very fine paint brush, the combination will look very nice indeed...again in my very personal opinion and technique. Here is a 1/48 scale Tamiya Kawanishi N1K1 finished in the above description. The top wings and fuselage was done with salt, the lower parts/floating devices where made by brush and testors chorme silver bottle paint. Hope it helps!!
