I thought I’d make a thread for this and show what I do while I’m doing some of this.
For the ruddy brown areas I use a four part process starting with Ace Premium Primer in Red Oxide. This is too red but establishes a base color.
I follow that with a light coat of Ace Rust Stop Ruddy Brown Primer. This may be hard to find now but something similar must be out there. I use very little so one can will paint quite a few props. What I do is make quick passes about six inches away to “dust” the prop until I like the result. Too close and you get too much paint, too far and the surface gets very rough from dried paint collecting. Anyway, what I’m looking for is a darker but mottled appearance.
A cap comparison for reference.
The third step is using plain old Testors, or Model Master Flat Black, in an airbrush. The spray pattern should be about 1/4" wide an inch away and the paint volume very light. This way you can make as many passes as needed until the saturation looks right with little fear of overdoing it on the first pass. I use this mostly over all the edges, borders, and details, but will also darken the overall prop to my liking to look like dirt accumulation from handling.
I’ll likely go over this one again with the black to make it darker after the rods are painted.
Here’s an earlier paint job using the black to make it look dirty from use, and showing the last step which is silver dry brushing.
I’ll get back to this with the current pieces in progress.