What color should A/C exhausts be? Black, rust, or a mystery color called burned iron? Or a clever combination of all three?

It depends on how new they are. Brand new, they're bare metal, but once they've been heated up for a little bit they turn a rusty-burned metallic blackish-brownish colour. I ususlly paint mine flat black, then rub on rusty brown pastel chalk powder and pencil graphite.

Jet exhausts are sooty black on the inside except when they're off-white ceramic with sooty streaks, and bluish-orangish "hot metallic" colour on the outside.

Thanks Jessica. I painted mine a rusty brown then applied a black oil wash which probably resulted in a simlar result as yours. Just wanted to check on the choice of colors.

Burned iron is a mixture of flat black, copper and rust brown. I add Testors orange brown 1166 to the edges.

Depends on the aircraft but the photo above is a fair selection. Light aircraft are a grayish brown but we have to be careful as modern exhausts are usually stainless steel, WW2 exhausts were not intended to last so were often cheaper material.

Agreed - depends on the your subject and it's condition, length of service, and whether you're building it brand-new off the line or after a lengthy tour of service.


Generally I paint my exhausts Nato Black, or Alclad's wonderful Exhaust on the outside, straight flat black on the interior of the exhaust, and then I'll use MiG Pigment's rust on to give the outsides life - making sure to keep the inside of the pipe black.

Lets not forget what the exhausts are made of as well. Cast iron, alloy, stainless steel all take on a different color when exposed to heat over time.

Don't forget Alclad's pale burnt metal either, that and the above mentioned exhaust.
Julian

Also notice that on the picture that Edgar has posted that the forward pipes have less discolouration to them, probably because it is cooled by the air flow? Basically no exhaust pipe is just one colour, but the cobination of effects of heat and moisture etc. I try and replicate the effects by starting with the metallic colour of the exhaust and then adding the effects, black, brown, blue, rust etc. Have fun

The lighter colour is caused by a thin layer of lead deposited by the exhaust gases. It is derived from the additive lead tetra ethyl.

Exhausts do not normally rust. Rusting is an electrochemical process that requires the presence of moisture. Rust is an amorphous, flaky, porous material consisting of hydrated red and brown iron oxides.

e.g., hydrated iron(III) Fe2O3·nH2O and iron oxide-hydroxide FeO(OH)·Fe(OH)3.

Heat oxidation results in a thin, hard patina of black (magnetite, Fe3O4 ) and brown iron oxides. These provide a measure of protection against rusting and it is called a passivation layer. Skilled blacksmiths can control this oxidation to produce a protective layer of magnetite in a process called 'bluing'.

Usually I paint my exhausts with true metal paints , adding some Dark Earth BS450. It's not so cheap but looks like real.

all depends what you mean by "exhaust". The exhausts of piston engines are totally different things but the exhausts of jet engines (but that is kicking in an open door).

Forjet engines it largely depends on the material (sometimes quite exotic) used and whether the jet is frequently using afterburner (resulting in high heat of the exhaust pipe).

I ususally prime jet exhausts in grey, and then aplly alclad "jet exhaust". In some cases I add some detail with a mist of alclad Aluminium, or "heated exhaust blue".

For reference I can only refer to pictures of the real thing. there is no overall solution or color. some exhausts are even white on the inside.

Another line of discussion is the colour of exhaust collector rings such as on the Bristol Mercury radial engines (Gloster Gladiator, Fairey Swordfish etc.). The material isn't iron.