Unfortunately, I'm not exactly sure how I ended up with the crackling effect. My theory is that the hairspray layer was too thick, my final coat was too thick, or a combination of both. More experimentation will be required to know for sure...
Here is a quick summary of the "Hairspray Method":
- Paint basecoat of rust colors (spray or brush, acrylic or enamel)
- Seal with a non-water based clear sealer
- Spray with hairspray
- Spray acrylic overcoat (with an airbrush so the hairspray doesn't melt away prematurely) the color the piece would be when 'new'
- Using a stiff bristled brush, wet the areas you want to have worn and brush away the overcoat to reveal the rust