Spatter:
I forgot to mention a technique I used to get the detailed weathering to look right. There's a lot of spatter on the original ILM models. Here's a shot of the real Red 3 showing a pretty clear example:
I first tried replicating this by flicking brush bristles, but that tends to get paint everywhere. I masked off areas where I didn't want paint to go, but I was rarely happy with the results. It's too unpredictable. Then I tried blasting air from my airbrush across a paintbrush dipped in paint. I had good luck with this technique on my AT-AT build, but it's very dependent on the thickness of the paint. If the paint is too thin it just goes on like it was airbrushed. I had to wipe off the fuselage a couple of times while I was trying to replicate this specific bit of spatter with that technique.
I should mention that after I was happy with the wash and the misting coats, I did apply a coat of matte varnish to protect everything I'd done so far when it came time to start doing the serious weathering which allowed me to wipe off mistakes without damaging what I'd already done..
I don't know how they did the spatters at ILM, but here's what worked best for me. With a double action airbrush, if you don't let the trigger forward to it's stop before you lift up to shut off the airflow, paint will build up around the tip. Then, when you next push the trigger down (but don't pull back!), that extra paint will blast out in a splatter of dots. It looks perfect! I discovered it by accident because I was trying to figure out a way to start and stop my airbrush while it was still pointed at the model without getting spatter. Then I thought I could use that spatter for good! Here's a detail:
Earlier in this thread I said it's really hard to match something that's a result of a random technique and this is a good example. I wasn't about to try and match every dot of paint to the original. My spatter is perhaps a bit overdone, but it gives the model the same general feeling as the original I think. If that makes any sense. And also, at 1/72nd scale, the dots are almost invisible to the naked eye, but you'd miss them if they weren't there.
Anyway, I recommend taking some scrap plastic, or even just paper, and trying to develop a good spatter technique with a double action airbrush. Again, the trick is to release the trigger abruptly while spraying. Then aim where you want your splatter and press the trigger down, but without pulling it back (that would spray paint everywhere). You should get a blast of air that blows out the trapped paint in the tip and gives you a nice small, and semi-controllable, spatter of dots.
I should mention that I use an Iwata Eclipse HP-CS with a .35mm needle, because no doubt that will affect things.