Based on what I’ve read, Hairspray is used a lot. You can check our How To archives here, because many have said how exactly they get the results they want!
I’ll be making my second attempt with the Ki84 Frank I’ve got underway. My first attempt was with this Raiden and I made some mistakes. I went down the hairspray technique. Prime, alclad aluminum coat, hairspray, then color coat. Hit it with a toothbrush to your liking. I think I didn’t let my coats cure enough or the alclad was affected by the hairspray as I got down to primer/bare plastic in some cases. I’ll keep trying
I usually paint on chipping, but I’ve used the salt technique, too:
Once you have on the color you want the chipping to reveal, eg, a natural metal color, and it’s dried/cured, apply a little water to the surfaces where you want chipping to show
Using salt with large granules, like kosher salt, for example, sprinkle the salt over the wet areas, and let it dry
Apply your next color coat to the area. Spraying will be ideal, rattlecan or airbrush
When the color coat has dried/cured, use a brush (eg, an old paintbrush, or even an old, worn toothbrush) and brush off the salt, leaving areas of “chipped” paint showing the material underneath
I also used table salt on one model. It worked OK, but it was a little more difficult to get the kind of chipping look I wanted.
It really depends on you, the effect you’re looking for, and your own familiarity with the techniques and your skill, to say whether one chipping technique is better than another. For example, if I want to show a little wear on the wing walks of a US Navy SBD, I might just paint the chips by hand. It’s not worth it to me to apply the effort of the salt or hairspray techniques for that effect, when I can just dip the brush. But for a Zero that was stranded at Rabaul in 1943, I want to cover larger areas, and then those techniques work better for me and the effort is worth it.