PC10

[Nick Millman]

As someone who has long believed the PC10 pigmentation to have been a mixture of yellow ochre and lampblack it was a surprise to find an AID approved 1916 RAF formula citing yellow ochre (40 lbs), umber (30 lbs), red ochre (40 oz), Chinese blue (25 oz for darkening) and lampblack ("few ounces" only where further darkening was required). It makes me think that there may have been alternative formulae approved at different times, perhaps in response to pigment availability. These proportional measures of fairly standard pigments allow a good approximate reproduction of the colour as intended by this particular formula. It is pretty "muddy" with very little green caste to it. The green appearance is produced by the interaction of the yellow ochre and Chinese blue but is highly dependent on the purity of the former and the mixing of the latter. Chinese blue is really a high grade and more expensive variant of Prussian blue (aka "Engineers Blue" approx RGB 0 49 83 as typical) but with a slightly greener appearance. It is an interesting colour because it can sometimes impart a "bronze" appearance dependent upon the proportional mix to binder and solvent which is critical to achieve clean colour.

Unsurprisingly, the way this colour is mixed can result in slightly more greenish or slightly more brownish variants.

The rest of the ingredients, for a 100 gallon batch, were 260 lbs of Nitrocellulose "syrup", 50 lbs of Castor oil, 20 gallons of Methylethylketone or acetone, 15 gallons of Butyl or amyl acetate, 15 gallons of methylated spirit, 15 lbs of Benzol and 74 lbs of pigment powder (as above).

Edited December 14, 2010 by Nick Millman

[SARowl]

Nick,

If SE5s of 1917 were PC10, it was definitely brown. On page 144 of 'Sagittarius Rising' Cecil Lewis describes the 56 Sqn SE5s "The Squadron sets out eleven strong on the evening patrol. Eleven chocolate-coloured..."

John

[Nick Millman]

Nick,

If SE5s of 1917 were PC10, it was definitely brown. On page 144 of 'Sagittarius Rising' Cecil Lewis describes the 56 Sqn SE5s "The Squadron sets out eleven strong on the evening patrol. Eleven chocolate-coloured..."

John

No, I don't buy that "definitely brown"! You are in danger of over-simplifying multiples based on a subjective, individual perception of one specific aircraft type at one point in time under a specific set of circumstances. If it was "definitely" brown one has to wonder why the dopes were not just described as "brown" rather than as "dark khaki". But then, many do still describe British Army khaki uniforms as "brown". Brown, like chocolate, comes in an infinite variety of appearances and whilst seeming at first glance to simplify the issue merely exchanges one set of imponderables for another. If it was "definitely brown" what shade of brown? If it was "chocolate-coloured" what type of chocolate?

The article on PC10 in Windsock International Vol.4 No.2 (Summer 1988) clearly evidences a range of revised pigmented varnishes where for example the requirements for the yellow ochre pigment changed in terms of the minimum percentage of ferric oxide required in that pigment, from 30% in early varnishes to not less than 60% in the later varnishes. This percentage has a direct bearing on the quality of the ochre and the degree to which "brown" is perceived in the appearance of the final colour, but there are several other factors at work, including the "ambering" effect of the clear varnish coats and the other constituent components which also varied.

The same article quotes Methuen values for a PC10 colour range as compiled in a useful table by Ian D Huntley pertaining to fabric condition and colour, based on both original fabric samples and reconstructed paint samples made to the original specifications. I won't cite the Methuen values as they are meaningless unless you have a copy of the Methuen book, but Mr Huntley's colour descriptions of appearances within the variable range are as follows:-

Lightest - Greenish-ochre

Normal - Greenish-brown

Dark - Brown-green

Darkest - Almost all brown

As you can see "chocolate-coloured" sits perfectly comfortably within this range but is not the whole story, whilst "definitely brown" as a description for all PC10 appearances does not. One cannot escape the "green" element in three of the descriptions given and, indeed, if you experiment with the original pigments yourself, you will understand why.

The same issue arises with the Japanese Army colour "yellow-green No.7" which was developed directly from PC10, first in dopes and then in paints for metals. An eyewitness also described one example of that as "chocolate bar brown" but it is not the whole story. The colour was effectively an olive or khaki drab, with an appearance ranging from more green to more brown.

The Windsock article only mentions yellow ochre and lamp black pigments, as do some other articles on the subject, which is why the AID approved 1916 RAF formula is interesting and, I thought, worth mentioning here.

[John Aero]

As Nick has pointed out this is a very difficult subject, I thought that the "modern thinking" was that PC10 was the early Greener end of the Khaki colour and that PC.12 was now thought to be the later produced "Brown" end of Khaki and not the Red middle eastern colour which has often been stated.

What I do know is that the tips of my very original Avro 504A propeller which are doped PC.10 over fabric are a very greyish Green.

John

[Test Graham]

There is another literary source - I thought it Winged Victory but have been unable to find it in two editions - describing the difference in falling weckage in a dogfight. German wreckage being multi-coloured but British being brown.

[SARowl]

I still no wiser which colour PC10 was. I think I'll stick to a darkish khaki, because I think the green that some modelers use is wrong...

[Trubbie]

Thanks for that information, Nick.

This really does show how it is possible to get such a range of tones, and I'm going to try some experiments with oil paints to see how it works out.

Also, the change of ferric oxide content in the yellow orchre pigment is a possible factor in the matter, although how I can replicate that is uncertain!.

Regards,

Trubbie

PS Should the '.....1916 RAF Formula' be the '.......RFC Formula'? Or was it written post WW1?

[Nick Millman]

Thanks for that information, Nick.

This really does show how it is possible to get such a range of tones, and I'm going to try some experiments with oil paints to see how it works out.

Also, the change of ferric oxide content in the yellow orchre pigment is a possible factor in the matter, although how I can replicate that is uncertain!.

Regards,

Trubbie

PS Should the '.....1916 RAF Formula' be the '.......RFC Formula'? Or was it written post WW1?

I should have clarified. In this case RAF = Royal Aircraft Factory!

Out of interest, over 30 years ago Ray Rimmel built a model of the S.E.5a as No.1 for his "RAF Museum Aircraft in Miniature" series in Scale Models magazine and described his choice of paint thus:-

"The Khaki colour of the model is mixed from two parts of Humbrol Dark Earth and one part of Black, once this has had a good coat of semi-gloss polyurethane, a shade similar to the full size is apparent; it even looks green in some lights!"

G.A.G.Cox's 1957 scale drawings accompanying the article refer to the top surface colour as "Khaki green" and I have seen this term given as the official colour description of PC10 in other references.

Sometimes the perception of these olive drabs is relative. A typical "average" sample of JAAF #7 viewed adjacent to true browns appears more green, but when viewed adjacent to strong viridian greens it looks more brown.

[Dave Fleming]

Humbrol's 106 (or was it 108?) was a very good match for PC10, being a browny-green. Too many have quoted the lamp black/yellow ochre formula as THE mix for PC10, when in fact there appear to have been several (One the 'experimental' formula, one the production? Or changing as time goes on?)

As John says, the red Oxide shade long thought to be PC-12 is more likely to be AMAPDT (or similar letters) the post war tropical shade - PC12 was red oxide and lamp black, but mix thoise two pigments and you get a shade that could easily e described as 'chocolate'

Bruce Robertson gives a good history of the RFC/RAF pigmented varnishes in his book on British Aircraft Colours for Windsock

[John Aero]

I feel that SARowl's approach is a little closed minded in view of the erudite answers from such as Nick.

I have on my desk the late Owen Thetford's personal copy of his book "Camouflage 14-18 Aircraft" (1943) with lovely colour illustrations by the great Rupert Moore.

In it he writes, ...1916..... the wartime Khaki Green camouflage dope had been standardised.... It varied in hue very considerably and ranged from a Dark Olive Green to a light Khaki and was seen in many intervening shades.

This suggests to me that the pioneers of modelling writing were well aware of the variations even then and they were closer by far to the event. The delightful Moore ilustrations , and bearing in mind early colour printing, all show a Greyish Green colour which match my Avro 504A prop tips very well.

Was it Cadburys, Bournville or Belgian chocolate and where was the light? Paint flying helmets brown leather, is the usual instruction, well my 1916 example is Orange Yellow.

John

[SARowl]

I feel that SARowl's approach is a little closed minded in view of the erudite answers from such as Nick.

John,

I was quoting from Cecil Lewis's book. As an SE5 pilot and accomplished author his words carry alot of authority. I accept that chocolate brown covers a very wide range of shades, tones and hues, and sounds better than

Eleven greenish-grey with a khaki hue aeroplanes...

.

This thread has just emphasised the problem that I was trying (badly) to explain. Talk to three different people and you will get three different colours for PC10. So I thought I would stick to Cecil Lewis's description, but I'm willing to be persauded otherwise.

John

[Nick Millman]

Talk to three different people and you will get three different colours for PC10. So I thought I would stick to Cecil Lewis's description, but I'm willing to be persauded otherwise.

John

Sometimes you just have to accept that colour is not as cut and dried as (some) modellers want it to be. I think it depends on which three people you talk to and what the three different colours are based on! As for Lewis' credentials, Ian D Huntley was a colour archivist who had based his analysis on both the original formula and extant samples of actual fabric. John Aero cites another credible source in C Rupert Moore who matched colours contemporaneously from real aircraft. To rule out the results of their analyses in favour of a single description (not an analysis) from a man who may well have been an SE5 pilot and accomplished author but whose colour perception is a completely unknown quantity does seem close minded.

And btw, my post was not intended to persuade you (or anyone else) to paint your models any way other than how you want. But "I use Humbrol xyz" is no real basis for a discussion of the historical record I'm afraid.

[avro683]

Humbrol's 106 (or was it 108?) was a very good match for PC10, being a browny-green. Too many have quoted the lamp black/yellow ochre formula as THE mix for PC10, when in fact there appear to have been several (One the 'experimental' formula, one the production? Or changing as time goes on?)

As John says, the red Oxide shade long thought to be PC-12 is more likely to be AMAPDT (or similar letters) the post war tropical shade - PC12 was red oxide and lamp black, but mix thoise two pigments and you get a shade that could easily e described as 'chocolate'

Bruce Robertson gives a good history of the RFC/RAF pigmented varnishes in his book on British Aircraft Colours for Windsock

106 is Ocean Grey so it's more likely to be 108? Also, according to the chaps at Wingnut Wings, Humbrol 155 (Olive Drab) is a match for PC10.

Tony

[Nick Millman]

106 is Ocean Grey so it's more likely to be 108? Also, according to the chaps at Wingnut Wings, Humbrol 155 (Olive Drab) is a match for PC10.

Tony

Humbrol 155 is a good match for JAAF #7 too.

[MilneBay]

Personally I mix a separate batch for each model. To my mind this captures the variability, so models I've built tend to range across from a colour close to Olive Drab through to a more brown version. All seem to fall within the various descriptions I've read. I wonder also if in service the colour aged to a browner shade than when it was fresh.

[Rowan Broadbent]

Personally I mix a separate batch for each model. To my mind this captures the variability, so models I've built tend to range across from a colour close to Olive Drab through to a more brown version. All seem to fall within the various descriptions I've read. I wonder also if in service the colour aged to a browner shade than when it was fresh.

I doubt that there was much ageing in service - as service was measured in months or weeks, generally. Colour change over the intervening 90+ years is another thing, but still massively overestimated, in my view. If one considers the colour changes to old master paintings, the actual colours have changed little over four or five hundred years but the varnish coatings and accumulation of general atmospheric filth are the things which change the appearance the most. I once had a pair of oil paintings from the sixteenth century, both painted on wood and after having them professionally cleaned the difference was frankly incredible - the paint colours were transformed and they could have been painted yesterday. Where aircraft colours used were subject to change (fading in this case, due to the effects of UV light), such as the early reds and blues of the RFC cockades, the formulations were changed to prevent this and VR2 and VB3 were almost totally resistant to such damage. Whether the changes to the PC10 formulae were for the same reasons seems to be unrecorded, or at least not revealed to date.

Of course, the accumulation of oil (particularly burnt Castor oil, in the case of rotary powered aeroplnes), grease, dirt and exhaust stains had a marked impact, but this was localised and wouldn't have affected those parts not subjected to either their direct effects or the effects of cleaning them off.

Admittedly the choice of paint pigments and the carrying medium will have an impact, but the compounds used in the manufacture of the pigments are, in the main, chemically stable and will change little over considerable periods. "Oxidation" is often named as a culprit, but oxidation of an oxide (many of the pigments were oxides of one sort or another) is almost a contradiction in terms (my A level chemistry is pretty rusty; some oxides can change, but that process needs specific and harsh conditions such as excessive heat and pressure, which would destroy the fabric in any case!).

[Dave Fleming]

Where aircraft colours used were subject to change (fading in this case, due to the effects of UV light), such as the early reds and blues of the RFC cockades, the formulations were changed to prevent this and VR2 and VB3 were almost totally resistant to such damage. Whether the changes to the PC10 formulae were for the same reasons seems to be unrecorded, or at least not revealed to date.

Added to which, the whole point of PC10/12 etc were as protective varnishes, to protect the linen from UV light - the colour was almost a by-product

[Nick Millman]

"Oxidation" is often named as a culprit, but oxidation of an oxide (many of the pigments were oxides of one sort or another) is almost a contradiction in terms (my A level chemistry is pretty rusty; some oxides can change, but that process needs specific and harsh conditions such as excessive heat and pressure, which would destroy the fabric in any case!).

There is more than one "culprit" and attributing (or ruling out) colour shift by citing just one factor is too simplistic. In addition to fading or colour loss/retention there is, for example, chalking of the painted surface and yellowing of the binder to consider. With the greatest respect a 16th century oil painting cannot usefully be compared to the protective coatings on a 20th century war machine. Look again at the ingredients of the dope listed in my first post and then compare that to what you might typically find in 16th century oil paint. There are many factors involved and they are usually interactive and cumulative. 16th Century oil paintings are not usually subject to long periods directly exposed to changing environments at different speeds, altitudes and temperatures or to a regular regime of maintenance and handling involving various solvents. They do not have hot engines discharging various pollutants over them and attached to them. Even oxide pigments can shift as a result of ageing or pollutants (and other factors) although they are not sensitive to light - q.v. Michaelski's "Light, Ultraviolet and Infrared" of the Canadian Conservation Institute. Paint changes from the moment it leaves the tin and continues to do so, from a combination of internal and external factors, the latter both passive and active, but the critical questions are always how much and how to quantify that change.

In the meantime I found some more details about Ian D Huntley's analysis:-

The analysis was conducted on behalf of the RAeS Historic Aircraft Maintenance Group, specification committee.

He based his findings on:

1) All of the Advisory Committee for Aeronautics reports and memoranda.

2) The differing specified methods for application of the coating.

3) The various "official" specifications for PC10.

4) A series of experiments intended to reproduce an "early war" PC10.

5) Paint chips from the Ripolin Paint Co. dated 1916, and found at Fairey Aviation in 1950.

6) Existing samples of preserved fabric.

The experiments were carried out by professional chemists and followed the specification attached to a 1915 Ministry of Munitions contract placed with Ripolin:

MOM contract A1791/44/c/1915 for Protective Covering PC10.

Nitro-cellulose Syrup 232 lbs

Butyl or Amyl Acetate 15 gallons

Alcohol 15 gallons

Benzol 15 gallons

Acetone 20 gallons

Castor oil 52 lbs

Pigment: 142 lbs Yellow ochre (34% Ferric Oxide) and 8 lbs Carbon black 8 lbs

They were allowed to add small quantities of red or brown ochre to get a match to the standard if necessary.

The result was described as "green tinged with brown". Subsequent experiments with a higher purity of Ferric Oxide resulted in what was described as "red-brown" when the purity reached 60% plus.

The differing specifications for application varied the number of coats of pigment and that would also have affected the appearance. With that in mind I think the Methuen values cited by Mr Huntley in the Windsock article and the paint chips included therein might be considered reliable.

What is not explained is why the Ferric Oxide percentage was increased over time, although a reasonable guess might be hazarded.

[Rowan Broadbent]

There is more than one "culprit" and attributing (or ruling out) colour shift by citing just one factor is too simplistic. In addition to fading or colour loss/retention there is, for example, chalking of the painted surface and yellowing of the binder to consider. With the greatest respect a 16th century oil painting cannot usefully be compared to the protective coatings on a 20th century war machine. Look again at the ingredients of the dope listed in my first post and then compare that to what you might typically find in 16th century oil paint. There are many factors involved and they are usually interactive and cumulative. 16th Century oil paintings are not usually subject to long periods directly exposed to changing environments at different speeds, altitudes and temperatures or to a regular regime of maintenance and handling involving various solvents. They do not have hot engines discharging various pollutants over them and attached to them. Even oxide pigments can shift as a result of ageing or pollutants (and other factors) although they are not sensitive to light - q.v. Michaelski's "Light, Ultraviolet and Infrared" of the Canadian Conservation Institute. Paint changes from the moment it leaves the tin and continues to do so, from a combination of internal and external factors, the latter both passive and active, but the critical questions are always how much and how to quantify that change.

Sorry if you found my comment too simplistic but the effects you quote, relating to wear, masking and erosion, are localised to the areas affected by oil, fuel, exhaust staining and subsequent cleaning - I thought I'd covered that in the part of the post you didn't quote? I nowhere sought to "rule out" colour change, I simply suggested that I believed it to be overstated as far as the pigments were concerned. As to dismissing the comparison with old paintings, the basics hold true, any change of colour was not limited to a change in the pigment (which I still believe was very minor) but mainly to the medium in which that pigment is suspended. WWI Aeroplanes were not hung on walls with generations of tobacco smokers filling the air with their noxious residues, or at least, probably not very often. I really don't think that we are arguing different points at all.

In the meantime I found some more details about Ian D Huntley's analysis:-

The analysis was conducted on behalf of the RAeS Historic Aircraft Maintenance Group, specification committee.

He based his findings on:

1) All of the Advisory Committee for Aeronautics reports and memoranda.

2) The differing specified methods for application of the coating.

3) The various "official" specifications for PC10.

4) A series of experiments intended to reproduce an "early war" PC10.

5) Paint chips from the Ripolin Paint Co. dated 1916, and found at Fairey Aviation in 1950.

6) Existing samples of preserved fabric.

The experiments were carried out by professional chemists and followed the specification attached to a 1915 Ministry of Munitions contract placed with Ripolin:

MOM contract A1791/44/c/1915 for Protective Covering PC10.

Nitro-cellulose Syrup 232 lbs

Butyl or Amyl Acetate 15 gallons

Alcohol 15 gallons

Benzol 15 gallons

Acetone 20 gallons

Castor oil 52 lbs

Pigment: 142 lbs Yellow ochre (34% Ferric Oxide) and 8 lbs Carbon black 8 lbs

They were allowed to add small quantities of red or brown ochre to get a match to the standard if necessary.

The result was described as "green tinged with brown". Subsequent experiments with a higher purity of Ferric Oxide resulted in what was described as "red-brown" when the purity reached 60% plus.

The differing specifications for application varied the number of coats of pigment and that would also have affected the appearance. With that in mind I think the Methuen values cited by Mr Huntley in the Windsock article and the paint chips included therein might be considered reliable.

What is not explained is why the Ferric Oxide percentage was increased over time, although a reasonable guess might be hazarded.

Very interesting stuff. As you haven't hazarded a guess on the additional Ferric Oxide, let me take the risk.... As has already been stated by Dave Fleming, the primary purpose of PC10 (Protective Covering), at least initially, was to protect the underlying materials from UV light degradation and the camouflage effect was secondary or at least serendipitous. Hence the red brown colour of AMAPDT used post-war in the middle east was due to increased concentrations of ferric oxide (amongst other changes) to combat the higher UV experienced there. This was later replaced by Aluminium dope, of course, which was far more effective, offering reflective as well as masking properties. The increased amount of ferric oxide could have been either to increase the protection from UV or to enhance the colour to improve camouflage. My bet is on the former. It would also explain the oft-quoted view that earlier PC 10 formulations were greener and later ones browner.

If you haven't read it, Bruce Robertson's WWI British Aeroplane Colours and Markings published by Albatros Productions provides further insights, including the recipe for PC10 in your original post. It also clearly sets out that the Admiralty-specified PC12 contained only Red iron Oxide and Carbon Black as pigments

[Nick Millman]

There are circumstances in which pigment mixes can colour shift because one or more of the constituent pigments (on which the colour appearance depends) has less (or more) sensitivity to light. That can compromise the appearance of the colour as originally applied - sometimes quite significantly. In extreme cases there is sometimes no clue to the original colour appearance unless constituent pigments can be identified using Raman microscopy. Combinations of extreme heat and moisture tend to break the integrity of the coating more quickly and can also cause significant changes. Colour shift is recognised even in very modern and sophisticated coatings where the maximum extent of any shift over a specified period is guaranteed. It would be wrong to consider all pigments as stable and subject to shift only as the result of active external factors. The whole subject is complex and somewhat "how long is a piece of string". The tendency in modelling is to over-simplify it by considering selective factors - sun fading, etc., and assuming their effects are hard and fast. My use of the term "simplistic" was not intended to give offence!

On the subject of how much even a relatively small shift will affect the colour appearance, again "it depends". In some colour spaces even very small shifts can change the perceived hue from one thing to another. The green-brown space is one of these.

Re the red oxide I tend to agree with your guess but it would be interesting to "see the working" behind the changes! I don't have the book but thank you (and others) for mentioning it.

[Dave Fleming]

This was later replaced by Aluminium dope, of course, which was far more effective, offering reflective as well as masking properties.

From memory, the aluminium was applied over a red oxide primer as well.

[John Masters]

On 12/14/2010 at 11:30 AM, Nick Millman said:

260 lbs of Nitrocellulose "syrup", 50 lbs of Castor oil, 20 gallons of Methylethylketone or acetone, 15 gallons of Butyl or amyl acetate, 15 gallons of methylated spirit, 15 lbs of Benzol and 74 lbs of pigment powder (as above).

Yes..."After we make our aircraft out of dried spruce and canvas, we'll varnish them.  Then we'll pat them with dried, coloured,  gasoline."  Amazing.

 

I love the PC10 conversation.  It just goes 'round and 'round...🤪

[europapete]

well, this is fascinating stuff and we all try our best to be as accurate as we can. Personally, I will be happy just to get a model to the painting stage! lol. Regards, Pete in RI

[wombat]

Reading Bloody Paralyser at the moment, which claims there are fragments of fabric from 0/400s still around that show PC10 is definitely green. Though unhelpfully supplies no pictures of the same.

[europapete]

That's a good book, Wombat. I still have a couple of tins of Xtracolour Enamel, and it is a brownish green. I think Aviattic nailed it when they produced their PC10 fabric decals in half a dozen different shades!!!!  Regards, Pete in RI