As it turned out

This project was actually fun.
A client sent me 3 factory painted O scale brass PRR hoppers to be weathered.
He included rather specific requests for the different looks he wanted for the 3 cars, along with some very useful colour imagery.

These are just 2 of the images provided.
The challenge for me was to replicate the various looks with the mediums I had at hand.
I started by giving all 3 cars an India Ink wash. From there each car was sprayed with different tones of dirty rust colours, varying each car.
Once that dried, out came the artist oils for 2 of the cars. I blotched the sides in a random fashion varying the colour and dirt patterns between the cars and then pulled it together with some more overspray.
The third car wanted that blue/gray steel look from washed away paint. This was the look that I struggled with the most in my mind. It's easy to apply paint, real hard to remove. I made a mask from cardstock and held it off the car side about 1/4" and sprayed a blue/gray mix through it. The mask softened the edge and the thinness of the paint captured the look. The car I worried the most about turned out to be the easiest to do.

I'm rather pleased with my efforts and I've no doubt the client will be as well. That's cause I've been sending him progress images as this job went along.
I'm always careful with "heavy" weathering. So easy to go too far.