Hi Jody,
Having done a bit of this 'chipping' lark in Braille scale I hope I can help. I use standard ladies hairspray, best get the unscented if you don't want your hobby area smelling like a hairdresser's salon. I paint the model in its basecoat, this will depend on what you are doing and want to represent. I take my hairspray and decant some into my airbrush cup, then use it neat and give the model a few sprays, either to cover it if I am doing extensive chipping, or in localised areas if I am doing discreet chipping. I then spray the topcoat, now this is where you will have to be careful, only wet the area you are immediately working on and do your chips for that area before you move on. If you don't take time and do this you will probably not get the desired result you want. I use old paintbrushes, some cut down to make stipplers, toothpicks and pins to get the desired effects. After you have finished seal it all with varnish.
Here are some I did earlier...
Panzer Grey basecoat and Desert Yellow topcoat...
Three colour camouflage basecoat and dirty white topcoat...
Panzer Grey basecoat and Desert Yellow topcoat...
This one took a long time as there were so many elements to do, but it was fun.
Hope this helps, all the best,
Paul