I've not tried to do the hairspray for chipping though that does sound good. I've only tried it with worn whitewash on my T34/76. Not much chipping here.
On my T34/85 I did a bit more with chipping. I first painted a lighter color green in spots. After that I went over and near some of the spots with a dark red color, I think it was a Citadel games color called scab red. Then over and near that a very dark brown, again games paint called charred brown mixed very slightly with a steel color. The tow cables and lower front show this fairly well:
The Panzer IV/70 I did for the GB was done pretty much the same way for the chipping.
Using the sponge method is useful too though I think I got a bit carried away on my 234/1: