WWII Exhaust Color (Rust)

'Rust' for exhausts seems to be one of those long-held tropes for modeling---but it's mostly wrong, especially for service aircraft. Depending on the machine in question, colors range from steel to dark black/brown metal tones. I'll usually basecoat a charcoal grey---drybrush with a lighter grey for tone and highlighting---then lightly drybrush with a bronze tone, for a slight metallic feel.

As noted, good color photos are your best guide; but it's better to go by 'real' photos, rather than models, unless you see an effect that looks good, and want to reproduce it---nothing wrong with that.

Cheers

I agree with Greg. Steel/bronze. Maybe a little flat black for soot

I agree as well. I think the rust is over done on many kits. Most AC are maintained it fairly good order, with exceptions. I would do as mentioned above but I would also add rust to the tips to simulate the condensation the would roll out when the engines are cold and then that area would have some rust, but again, not heavily. Those manifolds and pipes would have to be subjected to wet condtions like a car would in order to form very much scale on the pipes themselves. What passes for great weathering on models is not often the case in real life, but it looks good to the modelers eye, usually.

BK

Exhausts can rust.  Steel pipes seem to be a bit more resistant than cast iron manifolds, however.  However, steel pipes can still oxidize in other ways, even stainless steel.  Very thin coatings of various oxides can form, and while these layers are still thinner than the wavelength of light they create colors due to interference filtering.  These colors are often red or yellow or blue.  The red/yellow hues can look like rust.  If you can't find pictures of 190s, just look for any color photos of colored pipes, even on newer piston aircraft.  In fact, many jet tailpipes take on such colored appearances.  Since that type of operation does not affect operation, and may tend to be self-limitating, ground crews may not bother to remove it. It just slowly changes in color as the layer gets thicker.

Greg that's the same kind of technique I use. Thanks for the feedback. I figured it might be like you said...a certain look catches on in modeling and becomes the "norm". It seemed like anything rusting in a plane would be replaced whenever possible. 

I sort of get a clue looking under the car.

The exhaust is on the skin of the airplane which for a world war 2 airplane is made of either duraluminium or regular aluminium sheets. It behaves a little differently than steel. It has a bronze tint on it. I went out and looked at the muffeler on my lawn mower and that's what I saw. Rust has a more earthy brown look to it.

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'.

Though not pertaining directly to your question, please remember that the fuel used by the Allies during WW2 was highly leaded. This leaves a light grey residue inside the exhaust pipes and just aft of the pipes. It's more noticeable on inline engined planes but can be seen behind radial exhausts, too.

With a BMW 801, this may not be the case, due to the use of synthetic fuels by the Germans and different additional compounds to boost the octane levels.

 

 

Chris