I’ve uploaded a video with a demonstration of how I paint and weather my propeller engine exhausts. I demonstrated using the supercharger on the 1/48 Tamiya P-38 Lightning.
I did not invent this technique! I first read about using thin coats of brown paint to simulate rust in JM Villalba’s FAQ book. I added Tamiya pigments to make the finish more random, blotchy and somewhat textured. I have been using this technique for years because it is quick, not messy and very controllable. I think it can be used for non aircraft subjects as well. For those wishing to see how I do it, here is a direct link to the video. Let me know what you think!