Hey, I have weathered a PC/Conrail Hopper, and I had this walthers CSX quad hopper kit that I built, and I thought I should weather it. Well Here it is, I went off CSX prototype photos. 
Looks good. If that was on a layout, I would have thought it was real. [tup][tup]
Looks good. What medium(s) did you use to weather the hopper?
Nicely none…[tup]
Its good to see realistic weathering versus the often overstated “rust bucket” weathering…
dry brushing, craft paints, washs on black
Very nice. I am weathering my rolling stock as we speak, and I just did a C&O hopper. The one thing that I might recommend is to get rid of some of the yellow markings. I have used very fine sandpaper to remove some of the yellow. Then I rub on some black chalk to cover up some more of the yellow and it also covers up the sanding on the black part of the hopper. Not sure if this is the best way to do it, however. On my old C&O hoppers I also use white chalk on and below the lettering to make it look like it the paint is fading and running. (The rust on the springs do not look that bad in real life!)
go to all sizes than, go to the box that says something like post to website
Each one you do is better than the one before, and this continues the trend. Best one yet. Keep at it!
The weathering looks good on the car. I do find that most modelers forget the trucks and wheels. I always paint the trucks with a mixed brown paint and a little lighter for the wheels. Have you dull coated it so the weathering won’t rub off?
Really nice.