I just finished a few CSX blue boxcars. CSX cars have a tendance to get incredibly chalky. I used some of the ideas in the "Fading Fast" thread for inspiration.
http://therailwire.net/forum/index.php/topic,16573.0.htmlMy solution included 3-4 parts zinc white, 1 part burnt sienna, 15-20 parts Tamiya thinner, 10 parts Testors Acryl semi-gloss, 10 parts Testors Acryl flat. The solution is very light and needs multiple coats to build up. I found the acrylics tube paints did a lot better than Tamiya transparent acrylics for some reason.
I first added some roof rust made from thinned burnt sienna tube paint. I applied it to the raised areas of the roof in some places to simulate areas where the galvanization has worn through. The color contrasts will be harsh, and that's okay.
I then sprayed the whole model with three to five coats of the fade mixture. The model will look chalky and flat. I added black powdered chalk around the doors and door rails to simulate rub-off from machinery during the loading/unloading process and dirt buildup. The cars were lightly dusted with weathering chalks and a "puffy" soft brush. The models were then sealed with a flat finish.
I hope to have pictures up soon.