GN 3529, an Athearn BB 40 Footer, was airbrushed using dust, and I painted the trucks. The western roads rolling stock would normally show different weathering patterns over their eastern counterparts. Most eastern stock will show rust, and abuse, where the western stock will show element wearing such as dust, dirt, fading, etc.
Here's a Reading Boxcar that just showed up on the property, Hard to believe it seemed like just yesterday it was bright and shiny
This was weathered using a product called Rustall, but you can make your own wash using Isopropyl alcohol and paint at a ratio of approximately 8 to 1, depending on how much color you want to add to the victim, er, project!
BEFORE:
In the upper right of the picture, you see an unusual color boxcar from the Erie Lackawanna. It's in the color i bought it, and the EL played with some different schemes.
AFTER:
And here's the car with a few years weathering added. This project took about thirty minutes to get it to this point. Not much time, and not much material make the car look a lot more realistic. It's not hard to do, either, as the wash settles around the raised areas. It's a trust thing!! But it works.