PRU Spitfire

[Ed Russell]

This quite small picture came from the collection of a 451 (Australian) Squadron veteran. It appears to be in the dark blue (Royal Blue, mixed colour?) scheme apparently used in the Mediterranean. I believe I have seen similar pictures, perhaps the same one. Can anyone shed any light on it?

[Super Aereo]

The "Royal Blue" scheme is mentioned on page 181 of "Eyes For The Phoenix" and also reported elsewhere as a locally mixed "Bosun Blue" (in Malta, IIRC?).

[Test Graham]

IIRC, Bosun Blue was the name of the ICI colour that it was primarily made from. Possibly this implies a link with the dark blue seen on Captain's boats on HM Ships?

Edited March 27, 2013 by Graham Boak

[VG 33]

Could it be an orthochromatic picture? I say that because the blades yellow tip seem very dark.

Patrick

[Bear13583]

Looks very similar to the Sword 72nd PR IV Tropical kit. Should be able to give you some idea of tone as it has both the PRU and Royal blues.

[MilneBay]

Could it be an orthochromatic picture? I say that because the blades yellow tip seem very dark.

Patrick

Looks like that to me - the tone shift in the fuselage roundel is a giveaway.

[Michael louey]

Hi Ed,

From memory of reading some narratives, this plane was loaned to 451 Squadron by one of the PRU squadrons. It is painted in Royal Blue. Here is a link to another shot of the plane (or a similar one) at the AWM site

http://www.awm.gov.au/collection/P00869.012

I have some more photos at home from the 451 squadron history and the serial for the plane.

Cheers

Michael

Edited March 27, 2013 by Michael louey

[Super Aereo]

According to SAM Combat Colours 2, Hawker Hurricane 1939-45, The "Royal Blue" was mixed from 5 gallons of a colour called ICI Bosun Blue, 3 pounds of black pigment and 16 pounds of zinc and turpentine, the resulting colour being fractionally darker than FS 35109.

Edited March 27, 2013 by Super Aereo

[VG 33]

Hi Ed,

From memory of reading some narratives, this plane was loaned to 451 Squadron by one of the PRU squadrons. It is painted in Royal Blue. Here is a link to another shot of the plane (or a similar one) at the AWM site

http://www.awm.gov.au/collection/P00869.012

I have some more photos at home from the 451 squadron history and the serial for the plane.

Cheers

Michael

Hi Michael

With this shot I have no doubt : the yellow tips are "light". Anyway I have already built a very dark blue Spitfire PR IV, BR416 with a white wash under and on the side of the fuselage.

Patrick

[Giorgio N]

I believe the roundels had been painted with the blue lighter than usual to provide some contrast.

It can not only be a shift due to the film or any filter, as the airframe colour was dark blue and this would have been affected too. Pictures of other aircrafts with standard roundels show the two blues to be very similar, why would the roundel blue be affected only ?

Similar roundels can be seen on other meditarranean or SEAC based PR Spitfires

[Ed Russell]

I say that because the blades yellow tip seem very dark.

It may well be an ortho picture and close examination of the original photograph shows the tips to be pretty much the same colour or, if anything, a fraction lighter than the blades. Here's a higher resolution pic of the blade which doesn't help much....

Other pictures in the album are taken at Rayak so it may well be the same aircraft as the AWM picture. I think the roundel is consistent with being a B-type against a Royal Blue background.

[feropete]

Hi Ed,

I believe that Spitfire PR.IV(T) in your photo to be BP904, which visited 451 Sqn RAAF for a while. It was operated by 1 PRU in the UK before being ferried to 1 PRU(ME).

Attached are some more shots of it, I believe, taken on the same day in fairly close succession. I believe that the film used was probably Orthochromatic. First, a quick comment on the eye and interpreting black and white photos.

The human eye reacts particularly to wavelengths in the green-yellow range, whereas both Orthochromatic and Panchromatic films are more sensitive to wavelengths in the blue range. The anomalies between how the human eye perceives colour and the tones recorded by black and white film means that unless the viewer of a photograph has a preconception of what the colours should be, he will have no idea what they truly are. Conversely, this can also lead to problems interpreting black and white photographs where the viewer goes in with a preconceived idea of what he believes are the colours represented by the tones on the print and convinces himself that is so. A classic case is a photo of a nice red apple with a yellow banana and a bunch of dark blue grapes. A print from an ortho film will show the apple as black, the banana as very dark and the grapes as a light colour. This is contra-intuitive to what the eye perceives. Pan film is somewhat better but far from perfect. In other words don't rely on your gut feeling when interpreting b/w photos; take some time to study how the different film types render tones on prints and how lens filters can affect those tones. It is always best to start with known colours, blue, red and the ultraviolet blue of the sky, examine their reproduction tones on the print, and then make a guess at the film etc used. Other major factors can be the colour of the incident light, (time of day), angle of the reflected light, quality of reflecting surface, (smooth/rough, gloss/matt paint), and degree of shadow. Of course a careless printer who gets his exposures and contrast wrong can still bugger up your attempted interpretation..

The first three shots below show some RAAF blokes checking out “the knobs” on that Spit. The light tone of the Roundel Blue and the dark tone of the Roundel Red are consistent with the film used being Orthochromatic. What is not consistent is the dark tone of the fuselage paint if it is Blue as suggested but, more of that later. In the side view, note that on the wing undersurfaces the Roundel Blue now registers as a darker tone than the Red. This is because the wing underside is lit by diffused reflected light which contains less long wave length light, (i.e. reds), and is biased more towards the blue end of the spectrum than the direct sunlight on the fuselage.

Below are another two shots, also taken at about the same time, but presenting as dramatically different prints. The first appears to have been taken using the same camera set up as the three above. The second is dramatically different in its tonal values.

Both Orthochromatic and Panchromatic films are very sensitive to radiation with wavelengths of 350 to 450nm. This range covers from near ultra-violet to light blue. These give an abnormally high density image on the negative, resulting in an abnormally light-toned area on the print. The small difference in light intensity between the blue sky and white clouds is completely lost on the negative and, it is impossible to produce a print where clouds are visible. For this reason most photographers carried a Yellow filter in their kit. This filter reduces the amount of ultraviolet and blue light that reaches the negative, reducing the density of the image of the sky on the negative and, allowing it to print as a darker tone. The shorter the light wave length, i.e. the further into the UV spectrum the light is, the stronger the effect.

I believe that, after taking the first shot, the photographer has whipped out his Yellow filter and taken another from the same position, a matter of seconds later. (Note that there has been little movement of the blokes around the aircraft). As can be seen the sky has been considerably darkened in tone, as intended, as has the Blue in the roundel. The Red has been lightened slightly in tone as would be expected. The dark blue of the ‘erk’s overalls also appears as a darker tone while the khaki clothing remains much the same.

What is particularly interesting is that the tone of the fuselage paint has been rendered as a dramatically darker tone on the print. This would suggest that this paint is such that it has been formulated to strongly reflect light in the ultraviolet region. To me this makes sense for an aircraft flying at high altitude and, further, would also tend to suggest that this machine has been painted, not with a “common garden variety” paint from normal stocks but with a paint specially developed for PR aircraft.

Now I have launched the cat into the pigeon cage, I will sit back and wait for comments from the photographic and paint experts out there.

I do have a question of my own for Edgar and the Spitfire experts out there. What are those four fasteners under the windscreen, just in front of the door, intended for?

Peter M

Edited April 4, 2013 by feropete

[gingerbob]

Very interesting, Peter! If you hadn't shown me the last shot, I'd have been tempted to suggest that the center of the fuselage roundel was "fuselage paint"- the tone and reflectivity seemed to be in perfect agreement. And, to display my ignorance, is it therefore theoretically possible to "triangulate" by taking B&W pictures with different film types and/or filters and then know what sorts (not exact, of course) of colours are represented?

Not wearing my 'Spitfire expert' hat, but might those four spots be where (how) some sort of control box has been mounted on the port sidewall in the cockpit?

bob

Edit: Like this?:

Edited April 2, 2013 by gingerbob

[Edgar]

. This would suggest that this paint is such that it has been formulated to strongly reflect light in the ultraviolet region. To me this makes sense for an aircraft flying at high altitude and, further, would also tend to suggest that this machine has been painted, not with a “common garden variety” paint from normal stocks but with a paint specially developed for PR aircraft.

The flaw, in that argument, is that fighter Spitfires could (and did) fly to the same heights as P.R. airframes; also, in all of the files that I've looked at, there's never a mention of different formulae for different heights.

There are, however, several references to P.R. units being given permission to paint their airframes to suit their own requirements, and not follow strict guidelines; this is why discussions, on specific P.R. colours, are likely to lead nowhere, since we simply don't know (and probably never will.)

I do have a question of my own for Edgar and the Spitfire experts out there. What are those four fasteners under the windscreen, just in front of the door, intended for?

Enlarging the photo, as much as possible, they look more like bolt heads, so, as Bob says, they seem most likely to be something to do with cockpit "internals," rather than anything on the outside surface.

Edgar

[Nick Millman]

Correspondence on the testing and selection of high altitude paint colours circa 1941 between the RAE and MAP Director of Scientific Research (courtesy of Edgar) give no indication of the selection of specially formulated pigments relating to the ultraviolet region (which itself is expressed in a variable nm range*) but appear to have centred on standard observations from the ground and standard MAP paint reflectivity ratings based on Professor Merton's theory regarding reflectivity at 40,000 feet. This promulgated the view that in order to match the appearance of the sky at such altitudes the blues used would need to be very much darker than those used at lower altitude. Of course within this was the question of pigment type and particle size creating those appearances but the overall impression given is of empirical research rather than UV wavelength theory. The testing covered existing "blues" such as Sky and Sky Blue together with darkened blues referred to by various names including light and dark shade Ultra Blue and Deep Sky.

* Sometimes given as 12.5nm to 375 nm but also expressed as UV-A (315-400nm), UB-B (280-315nm), and UV-C (100-280nm).

I agree that it is difficult if not impossible to assess paint colour from photographic images, even by triangulation, since reflectivity is dependent on the pigment particle scattering, reflecting or absorbing light which in turn is dependent on particle size and wavelength. The pigment is a particulate compound dispersed in a medium without being dissolved or appreciably altered, chemically or physically. When paint is applied over a substrate the dispersed pigment will absorb and scatter light thus creating a uniform "colour" (up to a point). The degree of scattering, hence opacity, is controlled by the difference between the refractive index of the pigment and that of the medium. Therefore in theory two paints of identical or similar "colour" to the human eye can appear to reflect differently in film emulsion because they actually consist of different types of pigment or different proportions of pigments. One example of this is the proportion of iron oxide to chrome oxide green in typical "olive drab" camouflage paints which combine "red" and "green" reflectivity. This can cause problems for the human eye let alone for the film type and emulsion. I'm by no means certain that the characteristics of the different film types can be so closely defined to the point of hard and fast "rules" about images since there seems to be significant debate about the effects caused using very general colour terms that do not encompass the subtleties of colours like MAP Sky or Olive Drab.

Nick

[gingerbob]

A bit of an aside, but the other consideration (in high-altitude camo) that I hadn't thought about until I read the files was relative position of the viewer. Seems obvious, but the difference between viewing from the same altitude, versus from beneath or somewhat below (at which angle?)... it just goes to show how hard it is to find the "perfect" camouflage!

bob

[ben_m]

And, to display my ignorance, is it therefore theoretically possible to "triangulate" by taking B&W pictures with different film types and/or filters and then know what sorts (not exact, of course) of colours are represented?

Off topic, but early many colour photographs were taken on black and white film using three exposures each with red green or blue filters. This is an example: (see here for a version with the three original black and white images).

Other colour processes used tiny colour filters (grains or lines of colour) over a black and white emulsion to create a colour image (e.g. Autochrome, DufayColor), which is also the technique used today on digital cameras with a Bayer pattern array of coloured filters over a CMOS or CCD sensor.

[feropete]

Not wearing my 'Spitfire expert' hat, but might those four spots be where (how) some sort of control box has been mounted on the port sidewall in the cockpit?
bob

Enlarging the photo, as much as possible, they look more like bolt heads, so, as Bob says, they seem most likely to be something to do with cockpit "internals," rather than anything on the outside surface.
Edgar

Seems like a logical explanation to me! Edgar, you appear to have misunderstood my use of the word 'fastener'. I was using the word in the engineering sense to describe a range of devices, screws, bolts, nuts, rivets, various propriety products, etc. used for fastening. I was deliberately vague in specifying the type of device. I did not mean to imply they were there to fasten an object to the outside of the aircraft. I had never noted them on a Spit before. Will have to look more closely in future.

If you hadn't shown me the last shot, I'd have been tempted to suggest that the center of the fuselage roundel was "fuselage paint"- the tone and reflectivity seemed to be in perfect agreement.
bob

Also my reaction when I first saw photos of that aircraft. I was forced to revise when I got that last shot.

And, to display my ignorance, is it therefore theoretically possible to "triangulate" by taking B&W pictures with different film types and/or filters and then know what sorts (not exact, of course) of colours are represented?
bob

In short, and as pointed out by Nick, no! On the other hand, if you have shots of the same subject, in much the same time frame, in both Ortho and Pan films or, in either film with and without a Yellow filter, it can be extremely helpful in assessing basic colours used. One example that comes to mind is that of a series of Official photos of a line up of 3 Sqn RAAF Kittyhawk IA aircraft preparing to take off. The undersurface colour renders as a dark tone on the print. Some artists have interpreted this as Being Mediterranean Blue or a similar colour. A look at the sky behind the aircraft shows it to be fairly dark in tone with a lovely cloud scape. The photographer, being a pro, has used a Yellow filter to get this effect. That in turn has darkened the blue of the roundel and the undersurface colour. Other, amateur photos without the use of a filter, of these aircraft show the tone of the undersurface colour to be much lighter, more in keeping with the expected Azure Blue. I can post some of those photos if they are of interest to you.

. This would suggest that this paint is such that it has been formulated to strongly reflect light in the ultraviolet region. To me this makes sense for an aircraft flying at high altitude and, further, would also tend to suggest that this machine has been painted, not with a “common garden variety” paint from normal stocks but with a paint specially developed for PR aircraft.

The flaw, in that argument, is that fighter Spitfires could (and did) fly to the same heights as P.R. airframes; also, in all of the files that I've looked at, there's never a mention of different formulae for different heights.
There are, however, several references to P.R. units being given permission to paint their airframes to suit their own requirements, and not follow strict guidelines; this is why discussions, on specific P.R. colours, are likely to lead nowhere, since we simply don't know (and probably never will.)
edgar

I should have said 'for an aircraft flying at high altitudes for long periods over enemy held territory'. I am, of course, aware that Spitfire fighters could achieve these altitudes. Maybe not different formulae but different colours. The UV reflectivity of colours increases as they approach the shorter wavelengths: Red reflects very little, very dark blue reflects quite a lot. I am also aware that PRU aircraft were a law unto themselves and agree with you that we will never know the full story on all their colour schemes.

Correspondence on the testing and selection of high altitude paint colours circa 1941 between the RAE and MAP Director of Scientific Research (courtesy of Edgar) give no indication of the selection of specially formulated pigments relating to the ultraviolet region (which itself is expressed in a variable nm range*) but appear to have centred on standard observations from the ground and standard MAP paint reflectivity ratings based on Professor Merton's theory regarding reflectivity at 40,000 feet. This promulgated the view that in order to match the appearance of the sky at such altitudes the blues used would need to be very much darker than those used at lower altitude. Of course within this was the question of pigment type and particle size creating those appearances but the overall impression given is of empirical research rather than UV wavelength theory. The testing covered existing "blues" such as Sky and Sky Blue together with darkened blues referred to by various names including light and dark shade Ultra Blue and Deep Sky.
Nick

I take your point that UV is not mentioned in RAE and the MAP DSR correspondence. However they seem to have recognised the fact that at high altitude the light spectrum is much stronger in the lower wave lengths, moving into the UV. Hence the selection of colours such as dark blues and violets for use at these altitudes would make sense. I suspect that the latter hue is probably close to what is on that Spit, rather than just a dark blue as has been suggested.

I agree that it is difficult if not impossible to assess paint colour from photographic images, even by triangulation, since reflectivity is dependent on the pigment particle scattering, reflecting or absorbing light which in turn is dependent on particle size and wavelength. The pigment is a particulate compound dispersed in a medium without being dissolved or appreciably altered, chemically or physically. When paint is applied over a substrate the dispersed pigment will absorb and scatter light thus creating a uniform "colour" (up to a point). The degree of scattering, hence opacity, is controlled by the difference between the refractive index of the pigment and that of the medium. Therefore in theory two paints of identical or similar "colour" to the human eye can appear to reflect differently in film emulsion because they actually consist of different types of pigment or different proportions of pigments. One example of this is the proportion of iron oxide to chrome oxide green in typical "olive drab" camouflage paints which combine "red" and "green" reflectivity. This can cause problems for the human eye let alone for the film type and emulsion. I'm by no means certain that the characteristics of the different film types can be so closely defined to the point of hard and fast "rules" about images since there seems to be significant debate about the effects caused using very general colour terms that do not encompass the subtleties of colours like MAP Sky or Olive Drab.
Nick

I agree with your comments about paint construction. I would be silly not to since your expertise is in this area. My own experience comes as a result of doing much scientific photography in R&D in aerodynamics, specifically flow visualization. In that period I learned quite a lot about film types, their construction and emulsions, filters, lighting and many other factors including taking photos to record a particular state of flow.

As to interpreting sixty year old b/w prints, if, and that is a very big if, you have some knowledge of photographic techniques you can make some educated guesses about colours from b/w photos. The first thing you do NOT do is look at a print and try to evaluate what colours the tones represent. Tones on B/W prints, (even those from Pan film), are not perceived naturally by the eye. First you must try to background the photo: photographer's experience, good camera or box brownie, plate or roll film, type of film, lighting, condition of subject and its finish, (as described in your comments), conditions in which film has been stored, quality of film processing and quality of print making, age of film and/or print, to name a few. Very rarely can we ever get this range of information but we can make estimates in some cases. Next you need to have any eye witness accounts and what colours that you may expect to see. By using some basic known colours, particularly dark blue and red as well as looking at sky and shadows you can get some indication as to film type and posible use of a filter. (Yellow and Orange/Yellow filters were the most common type used with B/W film but, beware others may have been used. Then you can try and interpret what you are seeing on the print, and always remember that your interpretation is little more than a guess.

Unfortunately many people writing about aircraft colours have little knowledge about photography. This includes some artists who interpret B/W photos with an artists eye for colour and tone which is often quite contradictory to what the tones on the photo are telling him/her. When a salesperson tells me about the wonderful colour illustrations in a book, I tell him I that I am not interested, as far as I am concerned the books value lies in its text and photos.

My apologies for waffling on so. To finish I am appending a photo issued by Kodak some seventy years ago to show how wonderful their 'new' Pan film was. It helps illustrate some of the tonal differences between Ortho and Pan films for those that may not be familiar with them. Left is Ortho, right Pan. I also recommend a look at the website that Ben has put up to see how much filters can change the appearance of a B/W print.

Peter M

Edited April 4, 2013 by feropete

[PFlint]

"Sorry.

This person moved or deleted the image.

Photobucket"

please re-post a working link to a photo.

[feropete]

"Sorry.

This person moved or deleted the image.

Photobucket"

please re-post a working link to a photo.

Mr Flint,

Your wish is my command!

B'gered if I know why Photobucket deleted the photos and put up that message. The originals were neither deleted or moved. This time I have moved them to another folder and re-posted, hope they last a little longer.

Peter M

[PFlint]

Yeah , if it was photobucket BETA it is just one big pain in the .......

that is why most people are now putting their images somewhere else.

(thanks for the repost of the image)

[Giorgio N]

Peter, thanks for the information you have posted !

However I'm left with a doubt now: what about the roundels ? Would it be possible for roundels in the standard blue to show up so differently if the aircraft is painted in overall dark blue, considering that it is unlikely that any of the paints have particular properties in the UV part of the spectrum ?

Alternatively, the aircraft might not be dark blue, however there are quite a few mentions of the use of such a colour, and other pictures hint at the use of this very dark blue.

[Nick Millman]

However I'm left with a doubt now: what about the roundels ? Would it be possible for roundels in the standard blue to show up so differently if the aircraft is painted in overall dark blue, considering that it is unlikely that any of the paints have particular properties in the UV part of the spectrum ?

Alternatively, the aircraft might not be dark blue, however there are quite a few mentions of the use of such a colour, and other pictures hint at the use of this very dark blue.

Not to usurp Peter's reply but in a word yes.

MAP Dull Blue has colour differences to Deep Sky, Dark Mediterranean Blue and PRU Blue (for example) of 7.86, 7.19 and 18.2 respectively (where less than 2.0 is a close match). RAE reflectivity figures for Dull Blue were 4%, for Dark Blue ('royal blue') 6%, for Deep Sky and Dark Med Blue 8%, and for PRU Blue 14% so all things being equal one could expect to see different tones for these colours in a monochrome image but the roundel should usually appear darker not lighter - unless it was painted in a different blue... The pigments used in the paints could have different reflective properties even though generically blue. In the first three photos shown in this thread the centre disc of the roundel appears exactly similar in tone to the airframe but we know that was probably not red...

Was the mystery colour a "very dark blue"? I have seen it described as "Bosun blue" and "royal blue", both of which could be legitimate colloquial descriptions for Deep Sky and Dark Med Blue. Geoff Thomas matched it to BS381c 105 Oxford Blue which is not as dark as 106 Royal Blue!

Nick

[Giorgio N]

Thanks Nick !

So assuming that the aircraft in the picture is in a dark blue, it's relatively safe to say that the blue in the roundel is indeed a lighter blue than usual, and not the effect of the use of different films and filters, right ?

Of course if the aircrafts are not painted in overall dark blue then if the blue of the roundel looks light because of film and filters, it would be interesting to try and understand the overall colour.

Regarding the MTO (and SEAC) PR Spitfires (and Hurricanes as well), the term bosun blue was not a colloquial description but was an ICI made paint used as part of the mix. According to "Eyes for the Phoenix", the mix included 5 gal. of bosun blue, 3 lbs of black pigment, 16 lbs of zinc powder and turpentine. Royal blue was indeed the colloquial description for the resulting colour.

The same book however mentions that use of deep sky and dark med blue on other aircrafts.

[Nick Millman]

Hi Giorgio

It is mysterious that the airframe appears darker than the blue of the roundel in all versions of the image shown here, suggesting that either the roundel is not a very dark blue or the airframe is not blue! The impression I got from Peter's comment above was that he thought the airframe might be more violet, e.g. the paint containing red pigment. Could the roundels have been painted in a lighter blue to show up better?

Re the blue formula it is not clear whether the "zinc powder" was zinc oxide or zinc sulphide. Both are white pigments that have chemical change qualities I won't go into here but zinc sulphide is a brilliant white that causes luminescence in some circumstances. Zinc oxide as a white pigment mixed with Prussian blue was long reported to catalyse colour fading but more recently there have been conflicting views on this prompted by experiments at the Doerner Institute which found that other white pigments were actually worse - so it is by no means cut and dried. Without knowing what the mix was precisely intended to achieve or the actual colour of Bosun Blue the suggested effect would be to "grey" the Bosun Blue slightly without necessarily darkening it. For modelling purposes probably enough to take Geoff Thomas' approximate match of FS 25051 but the fly in the ointment is Profile 14 of a PRU Hurricane in his 'Eyes of the Phoenix' (page 196) which is supposed to be in 'royal blue' but looks distinctly greyish-blue!

In Methuen Royal Blue (19C7) references Indigo Blue (18F3) the description of which is "the uniforms of the king's men" which might be a clue to Bosun Blue.

Nick