I've started to address this with the coal hopper cars. I've studied a lot of techniques, and tried many, and have come up with a method I'm happy with, that won't take forever. With adjustments in color, it will work on many different kinds of rolling stock, and on locomotives. I'm not brave enough to try one of my locomotives yet, but I'll get there as I do more and more. Practice, practice, practice!
I mentioned it won't take forever, and that's important! I was showing some photos of the finished portion of my railroad to a friend at work, who's never seen anything like it, and he remarked that he thought it was "museum quality". I had to argue that it really was not, and pointed out some flaws and some things that could be better or more realistic. Most attempts at modeling anything in a small scale will involve many compromises, and you have to stop and move on when you feel it is "good enough". My weathering method is no exception - my trains aren't destined for a museum display (nor should they be); I run 'em, and I want to get the weathering done in a reasonable amount of time, and move on!
Enjoy the video. In real time, from setup to cleanup, this lot of 10 cars took me about 3 hours. As I get better (and don't fart around filming it!), I'm sure I can cut this time in half, maybe a little more.
