I can't imagine a cotton ball working as well as open-cell foam - long, thin fibers won't give the desired random, splotchy effect. Also, if you try the sponge-weathering method, don't soak the sponge in paint. Instead, dab most of it off, as if you were doing a light stippling or a heavy-ish drybrush.
For slow and even metallic wear and tear, like that found on track links and ladder rungs, I'm a fan of using a soft pencil or graphite stick. Gives it a darker, more subtle metallic color than Boltgun Metal with a very even, muted sheen to it. Not necessarily the best for drawing on scratches, but it's great for textured surfaces and edges.
|