Thanks! On the scrap yards pieces, I sprayed them with a red oxide primer. Then lightly sprayed with black here and there.
Coated some parts with Beil-tan Green wash to get that copper corrosion look. Picked out other parts here and there with silver, washes and other colors.
If I had to do it over again, I should have primed them in black first, then sprayed them with the red oxide. That would have gave them greater contrast and depth.
Such a noob mistake on my part, but even so, they still turned out pretty nice.
For other pieces, I use lots of Fuegan orange wash. Especially on white paint spots left on the pieces.
Usually a thick wash sentiment is at the bottom of the bottle. Dig for it with your brush,
and you will get a really nice heavy rust color that will stand out. Yellow wash is good too.
Dry brushing or sponge also with red brown paint works well. Be sure to use only cheap brushes for such work.
If you really want to go hardcore, spray your piece with red oxide, and let dry completely.
Then spray it with hairspray, and sprinkle kosher salt (Its bigger and chunkier that regular table salt.)
Now spray you base color over that. When dry, use a toothbrush and scrape the salt off.
Where the salt is removed, it will reveal the red rust oxide underneath the base coat, and simulate paint peeling.
I used this method on my processor plant and first building.
It's a messy process, so be sure to have a cover over your table, or do it outside, as you will get salt everywhere.
The easy thing about doing scrap yard pieces is its is impossible to mess up. It's rusting decaying junk, after all!