Red primer on RAF Strike Wing Beaufighters?

[Collin]

Staring the detailing and weathering stage of my Beaufighter. Noticed in a lot of period pictures with red primer scattered around airframes?  Was this a standard maintenance practice to prime bare metal or patched areas?  What about the gun ports?  
 

From the looks of it Tamiya red/brown is a good match? 
 

Thanks for any insight on the matter. 
 

Cheers

Collin 

[KevinK]

The first coat of butyrate dope used on aircraft fabric is there to tauten and airproof it. It's red because it contains iron oxide, which is there as a fungal inhibitor.

 

At a pinch, an aircraft is serviceable after only the red dope application, so you sometimes see photos of aircraft with red doped patches showing, although a full and complete repair would involve a further application of silver dope as a UV barrier, and then whatever final camouflage finish was necessary to match the overall finish.

 

Yes, a red/brown would work - it's iron oxide.

Edited November 9, 2023 by KevinK
missing word

[ClaudioN]

7 hours ago, Collin said:

What about the gun ports?

Yes, plenty of red primer on the gun ports, particularly 20 mm cannon. I assume it was for protection against dust and moisture, possibly applied regularly after servicing?

[Giorgio N]

I'd expect the application of dope on the gun ports to be due to the use of fabric patches to close the ports, same as done on the wing mounted guns of Spitfire Hurricanes etc..

 

[KevinK]

By the way, on fabric it's not really a primer at all. The purpose of a primer is to provide a paint layer which will adhere better to an unpainted surface than will a top coat: cotton fabric will accept any paint so it doesn't need a primer. The red dope is there to tauten and airproof.

 

That's why the gunports have a red coloured covering, and yes, it's to help keep the guns dry (icing protection) and clean until combat.

 

On an aluminium alloy surface, such as an aircraft skin, a primer can be one of several colours, but red is unlikely. The function of a primer on metal - adhesion - requires a specific chemistry to bond the primer to the skin. This is - and was most commonly in WWII - a chromate, usually zinc chromate. This is in the yellow-green colour range.

[rossm]

Some primer around wing roots too - busy today but can look up details tonight or check Terry Higgins articles in Airfix Magazine around the time the new Airfix Beaufighter was released - PM an email address for scans.

[Collin]

Thanks all. Any really good photos out there detailing the primer work. Most photos just show it from afar. 
 

Cheers

Collin

[Selwyn]

7 hours ago, KevinK said:

The first coat of butyrate dope used on aircraft fabric is there to tauten and airproof it. It's red because it contains iron oxide, which is there as a fungal inhibitor.

 

At a pinch, an aircraft is serviceable after only the red dope application, so you sometimes see photos of aircraft with red doped patches showing, although a full and complete repair would involve a further application of silver dope as a UV barrier, and then whatever final camouflage finish was necessary to match the overall finish.

 

Yes, a red/brown would work - it's iron oxide.

Beaufighters were not fabric coated.

Selwyn

[Phoenix44]

As far as I know (which isn't far), UK manufacturers used a grey primer where printers were required. Zinc chromate was not used at all. 

[Paul Lucas]

British Primers c.1944

 

Dark Grey 33B/207, 208, 209, 447.

This was a similar colour to Dark Sea Grey.

 

Light Grey 33B/260, 261, 262, 448.

This was a similar colour to the modern colour Light Aircraft Grey.

 

Both of these were Cellulose and intended for use under either Cellulose or Synthetic top coats on materials other than fabric and magnesium alloy.

 

Yellow DTD 911 33B/213. For Cellulose or Synthetic finishes on magnesium alloy.

This was something like BS 381 No.55 Lemon in colour.

 

Red tautening dope DTD 83A 33B/124, 125, 126, 416.

This was to all intents and purposes the same colour as the 'dull' Red Used in the national markings.

Aluminium tautening dope DTD 83A 33B/541, 542, 543.

Clear tautening dope DTD 83A 33B/537, 538, 539.

Transparent tautening dope for light structures DTD 83A 33B/614, 615, 616.

All of these were intended for use with Cellulose finishes on fabric and external plywood.

 

Bristol finished Beaufighters in camouflage to DTD 308 that was a Cellulose based finish. There is a nice photo on page 11 of the Wingleader Beaufighter VIC, X and XI book where the paint specification stencil is clearly legible on the fuselage above the trailing edge of the wing root. As a Cellulose finish, the DTD 308 camouflage would have been compatible with having fabric treated with the Red shrinking dope to DTD 83A applied directly to it without stripping the extant paint finish back to bare metal before applying the fabric. 

 

Whether the dark patches visible in the photographs are Red or perhaps fresh Extra Dark Sea Grey applied to either an aged Extra Dark Sea Grey or Dark Sea Grey finish might be open to question.

 

Edited November 9, 2023 by Paul Lucas

[Graham Boak]

1 hour ago, Selwyn said:

Beaufighters were not fabric coated.

Selwyn

Indeed not, other than control surfaces and covers on gun ports.  However for minor battle damage a fabric patch could be and often was applied and doped to retain it.  This seems to be what the initial poster is observing.

[KevinK]

4 hours ago, Phoenix44 said:

As far as I know (which isn't far), UK manufacturers used a grey primer where printers were required. Zinc chromate was not used at all. 

 

Except on a few lesser-known types?

 

 

... and

 

 

[dogsbody]

This is from Aviaeology's decal set AOD72002m, RCAF Beaufighters:

 

 

 

 

Chris

[wmcgill]

1 hour ago, dogsbody said:

This is from Aviaeology's decal set AOD72002m, RCAF Beaufighters:

 

 

 

 

Chris

May I present exhibit "A", M'lud

[Phoenix44]

5 hours ago, KevinK said:

 

Except on a few lesser-known types?

 

 

... and

 

 

Ah these old claims again! Didn't Edgar & Nick Millman & others address this some years ago?

[KevinK]

So - what is it, if it isn't a chromate primer?

[Paul Lucas]

I obviously did not make myself sufficiently clear in my previous post.

 

Yellow DTD 911 was a Zinc Chromate finish.

 

This Specification was dated November 1940 and paragraph 7(b) stated that 

"The priming coat shall be free from lead driers and shall contain not less than 7.5 per cent by weight of zinc chrome (D.T.D. 377). Pigment used in conjunction with zinc chrome must be one or more of the following : lithopone, barium sulphate, titanium dioxide, zinc oxide, kaolin, red oxide of iron or green oxide of chromium."

 

Most of these other pigments are white, which goes some way towards explaining the somewhat pale shade of yellow that looks something like BS 381 No.55 Lemon.

 

 

 

[KevinK]

30 minutes ago, Paul Lucas said:

This Specification was dated November 1940 and paragraph 7(b) stated that 

"The priming coat shall be free from lead driers and shall contain not less than 7.5 per cent by weight of zinc chrome (D.T.D. 377). Pigment used in conjunction with zinc chrome must be one or more of the following : lithopone, barium sulphate, titanium dioxide, zinc oxide, kaolin, red oxide of iron or green oxide of chromium."

 That's very interesting - thank you, Paul.

 

As the "active ingredient" from a chemical point of view is - in this case - the zinc chromate, would you happen to have the spec for what the corresponding ingredient was in the other two? :

11 hours ago, Paul Lucas said:

Dark Grey 33B/207, 208, 209, 447.

This was a similar colour to Dark Sea Grey.

 

Light Grey 33B/260, 261, 262, 448.

This was a similar colour to the modern colour Light Aircraft Grey.

 

[Paul Lucas]

11 hours ago, KevinK said:

 That's very interesting - thank you, Paul.

 

As the "active ingredient" from a chemical point of view is - in this case - the zinc chromate, would you happen to have the spec for what the corresponding ingredient was in the other two? :

 

I'm afraid not.

The 33B references given were taken from DTD Technical Circular No.360 Issue 2 of December 1943 and were originally those allocated to the primer for DTD 308 'Air Ministry Specification for Matt Cellulose Finishes and Primer', issued in July 1936.

 

Unlike DTD 911 which was a Specification for an entire process, including things like acid baths and not just a paint finish, DTD 308 does not specify exactly how it's requirements were to be met. Under the heading 'Description' it states that 

"The materials shall consist of :-

(i) a pigmented primer, suitable for direct application to metal or timber; and 

(ii) a pigmented cellulose finishing coating, which shall be a solution of nitro or acetyl-cellulose in volatile solvents in which suitable pigments are incorporated. The finishing coating shall be suitable for application over the primer."

 

Under the heading 'Ingredients' all it says is 

"Solvents such as chlorinated compounds or other substances which may cause injury or discomfort to operators during or after application, shall not be used."

 

Every individual paint manufacturer had its own proprietary formulas for the aircraft finishes  that they produced and provided that they met the requirements of the Specification, the Air Ministry does not seem to have been bothered how this was accomplished.

 

I have no information on the individual aircraft finish manufacturers proprietary formulas.

 

Aircraft manufacturers seem to have been free to purchase their finishing materials from wherever they liked. I suspect, but cannot prove that Supermarine at Southampton obtained theirs from Cellon. Where Castle Bromwich obtained theirs from I have no real idea, though there was a manufacturer in Wolverhampton named 'Manders' which might be a possibility.

 

I don't know from where Hawker obtained their materials either, but I am fairly certain that there was no such colour as 'Hawker Yellow', a term that I have seen being bandied about on this site from time to time. Hawker didn't make paint. . .

 

Clearly, some British aircraft manufacturers did use a Yellow coloured primer, but to find out all the whys and wherefores you would need to have access to the relevant aircraft manufacturers documentation for each specific type of aircraft and this is information I do not have.

[John B (Sc)]

Is the first aircraft in 'KevinK's message a Defiant? 

I recognise the second type obviously, but that first one has me slightly puzzled - both by the configuration and the impressivley oversprayed work - looks like some of my modelling !  I know they were having to knock stuff out at speed, but why not either remove the wheels or roughly maskthem. That piant may nitbe good for rubber.  Also, the entire undercarriage leg has been sprayed. Was there no chrome piston section for the oleo. which presumably you would not want to spray. Or did that type use another shock absorbing system?

 

John B

[Graham Boak]

It's a Hurricane.  My impression that this is a rig in the training school rather than a part on the production line.  It is still rather messy...

[KevinK]

Thank you again, Paul.

 

I know that we - as modellers - are usually involved only in the colour/appearance of the material, but the engineer in me thought that we could get at the answers via knowing the materials properties and chemistry: clearly, this has yet to be found, if it still exists at all.