OK, so I'm painting this ridiculously large painting in photoshop for a project due this Thursday (darn thing is 9000 x 7000, have NO IDEA how I'm going to get it all done, ahh well

).
Anyway, here is a tiny fraction of what I'm working on so far (I'm calling it a bar):
It's a sort of bar that's attached to the right side of a futuristic chair, and this is a portion that comes up over the head (as you can see, I haven't gotten to the rest of the chair

).
Now I want to put rust on this thing, mostly around the screws and where the "holders" of the bar, if you will, meet right up with the bar.
Anyone got any idea of how to do rust? I mean, I found one photoshop tutorial that didn't work because my image area is too small (and it wasn't quite what I was going for). Anyone got any ideas?
Thanks,
~Jen