Has anybody tried a coat of transparent yellow/orange after the bluing to get the brassy color?
As long as the bluing process isn't "oily" it should work, though I wouldn't recommend it. It would look like you had encased the "blue" in yellowish plastic (and it probably wouldn't take much to peel it off).
If you go with the tinted clear coat method , you really want to put the bluing on the outside.
Here's the method (as posted in the first Sidkit thread):
1. Get a two-part automotive (matte if at all possible) clear coat paint and a GOLD CANDY pigment additive (or whatever color you want the metal to be). There are colored clears available in cans and from Tamiya, but they're not nearly as durable as a two-part, and you will want that durability later. Alsacorp has one called "clear4chrome" that also has candy pigments available, but there are others as well.
2. Spray the parts until you get your desired shade of gold/brass/bronze. The more layers, the darker and less transparent it will become. The metal will shine through the clear/candy preserving the look.
3. If you had to get a
glossy clear (quite probable... I've never heard of a matte 2-part clear paint) then you need to buff it with a good, gritty rubbing compound. Get one of those meant for SOLID auto paints that aren't supposed to be used on metallics and clears (we want to
destroy the gloss). Make sure you wash off the compound thoroughly with soap... you don't want any wax to remain. You can also use very fine grit (2000) paper to dull it down, but if you're working on a complex shape with lots of small spaces and corners, using rubbing paste/compound is easier.
4. Assemble your gun and spray the entire thing with an acrylic (water-based, like Tamiya acrylics) matte black, mixed with a little blue or brown depending on what effect you're after.
5. When it's cured, get a polishing cloth (or paper that won't easily break apart when wet) and get it moist with Ajax dish washing liquid (the regular kind) or a mild alcohol and then gently rub over the parts. After a while, the alcohol will take off the airbrushed acrylic coat, but not touch the gold automotive clear underneath.
I've used this technique lots of times with good results. It also works on things like Pulse Rifles if you substitute the first clear coat for a silver metallic. I used it on my Phillippes Mal pistol cast, substituting the clear with gold and on my Jayne LeMat, adding a black additive to the clear to give it a smoky appearance.
The finished result (with wood grips):