Thought I'd go ahead and throw in my two cents. Personally, what gives Star Wars such a unique look in the OT is the fact that everything has a weathered and old look to it. As a painter myself, there are a lot of techniques you can do to get that paint flaking look but in the whole scheme of things you want that weathered look to appear as authentic as possible. I think the best way to achieve this is by weathering it yourself through good old fashion layering and scratching. People have asked me in the past how you can get weathered effects when painting models, pottery, etc... and I usually tell them to find the simplest answer. In this case, if you want something to look scratched so that you can see a surface below it then why attempt to paint it when you can simulate the look yourself. Can't fake the real thing. Hope this helps.