Thursday, 28 October 2010

On Accuracy, Purple Rufes and The Real Colours of Zero B11-124 s/n 5349

A couple of threads on other forums have given me pause for thought on the subject of accuracy in modelling. Of course that concept is a stretchable piece of elastic which can look very different depending upon which particular angle you approach it from. I suppose that modelling in the main consists of both imitative and interpretative strands, the former being concerned with verifiable fact and the latter with speculation. Of course the line is blurred and interpretation itself covers not just informed conclusion but half-truths and also wilder, more adventurous forays. If you come at the "elastic" from one particular angle there is a tendency to frown at those who might approach it from others. But it is all a moving feast.

The subject of Japanese model aircraft accuracy is beset by a multitude of unknowns, but almost uniquely this air of genuine mystery appears to have obscured much of the verifiable fact too. I'm not sure why this is. I can't imagine seeing a thread pertaining to the Bf 109 develop in the way of that thread concerned with an aotake-primed Zero model. On the one hand a desire for knowledge was eventually professed but on the other hand, when it was given, the provider had been roundly condemned for spoiling the fun. Apparently it was all about the manner of delivery. When you criticise the accuracy of a model you must do so courteously and politely - or you'll be subject to a vehemently rude gang attack! And all that talk of "the usual suspects" had me smiling; "The creatures outside looked from pig to man, and from man to pig, and from pig to man again; but already it was impossible to say which was which." 

The model above depicts the mortal remains of Mitsubishi A6M2 Zero BII-124 s/n 5349 as it sat derelict on Melville Island in the 1970's. This Zero, from the carrier Hiryu and piloted by Hajimi Toyoshima, was shot down during a raid on Darwin on 19 February 1942, crash landing on Melville Island. The model was made by Owen Veal and the image kindly provided by Bob Alford in response to earlier "Purple Rufe" musings. Owen made the model in balsa then first primed it with a colour match to the red primer used on the real aircraft. A top coat was then applied, matched to the weathered grey of the aircraft finish at that time, then the whole was deliberately abraded to represent the aircraft exactly as it then appeared - weathered after some 30 years in the harsh environment of tropical sun and two seasons - wet and dry. Remind you of anything?

And above is the actual aircraft as it appeared on display in the Australian Aviation Heritage Centre in 2009.

Zero B11-124 on Melville Island in 1942

Contemporaneous intelligence reports describe this Zero as follows:-
  1. "Markings on rudder BI-124 (sic). Number on fuselage 5349. Aircraft finished grey, with red circles on mainplanes and fuselage. Two blue bands encircling fuselage at rear of red circle" (Sgt W A Beatty Fitter IIE 13 Sqn RAAF 7 March 1942)
  2. "From visual observation today, the opinion has been formed by the IO (Intelligence Officer) that the wreckage is not recent, it presented a somewhat bleached appearance, but in contradiction the red roundels . . . (do) not appear to have faded." (PO J A Evans IO 52 OBU Darwin - observation made from a B-25 of 18 NEI Sqn circra March 1943)
  3. "The remains of the Zeke were in remarkably good condition. Very little rust was observed. The anti-corrosive paint used is evidently very effective, wing tips showing red roundels were found. The red paint of the roundel was still very bright. A piece of the red roundel was brought back to show colour. . . the wings and body were silver grey in colour." (FO C D Pender IO 15 Fighter Sector 28 April 1943)

Zero B11-124 on Melville Island in 1942

Sample of paint surface from Zero B11-124 s/n 5349

Various samples of paint from s/n 5349 were examined and analysed. The paint surface which had oxidised and "chalked" was found to be similar in appearance to the Tamiya paint XF-76. However when buffed back to remove the oxidisation and chalking the paint surface was revealed to be glossy, darker and a different hue. The measured colour value of this surface was found to be almost exactly between Munsell 5 Y 5/2 and 5 Y 6/2 or very close to FS 595B value 16350 @ 1.51 (where a difference calculation of 2.0 or less = a close match) and to RAL 7034 Gelbgrau (Yellow Grey) @ 1.64. Further analysis suggested that as a result of thermal ageing this paint surface was probably slightly darker and yellower (browner) than the original had been. In other words the original paint was slightly lighter and greyer - with the emphasis on slightly. The "greenish" appearance of the paint is largely illusionary and the result of an interaction between two of the constituent pigments. The paint colour is also highly metamerismic, its appearance to the human eye significantly shifting under different forms of illumination.

Schematic of compared paint colour values

Rather surprisingly the remnants of Aotake extant on the reverse side of these pieces was found to be a brilliant, almost emerald, green rather than blue-green or blue, with an evident "metallic" appearance (see below).

Comparison of extant paint surface to Tamiya XF-76 (showing Aotake)

So, there are two verifiable facts here. The current appearance of the oxidised/chalked paint surface and the current appearance of the buffed back paint surface. To take this further involves making presumptions and/or conclusions drawn from experimental analysis. In order to believe that the buffed back paint surface accurately reveals the original paint colour we have to presume that:-

a) The concealed/protected surface colour has not shifted in colour; and

b) That the buffing back process has revealed the original surface appearance and not something else.

If we are to believe instead that the oxidised and chalked paint surface reveals the colour of the original paint then we must presume that the paint surface has not oxidised or chalked! In reality both positions are tenuous and almost impossible to insist on without further analysis, especially remotely where the dependency is on imagery rather than physical handling. Even after further analysis any conclusions that are drawn must depend on the perceived validity of that analysis. Those who have a strongly pre-determined opinion will not be swayed by any evidence, always finding reasons to question, challenge or disbelieve it. This response is also related to the approach where evidence is selected or presented in order to support a pre-determined, wished-for outcome. Unfortunately both are prevalent, especially in the world of modelling.

In fact the paint is on a journey the moment it leaves the tin and changes will depend not just on external factors, active and passive, but also on the inherent characteristics of the paint composition itself. Seeking to identify the precise original paint colour just from its current appearance is akin to asking someone where they were last Wednesday and receiving the answer that today they are in Basingstoke. That fact may or may not be relevant.

In pure modelling terms this probably doesn't matter too much, because an individual modeller might legitimately determine to paint his Zero to represent paint at any point on this journey. In that sense the two "camps" (there may be more than two!) are not that far apart, each championing a paint colour based on a specific point in the journey. However, for those interested in the likely identity of the original paint colour as specified and mixed for the tin, further work is necessary. 

Much more important than appearance in the consideration of real paint is composition. This is surprisingly overlooked even by those passionate about the subject, who tend to focus on paint standards and visual appearance matching. The interaction of known pigments, additives and solvents is quantifiable both by established principle and by experimentation. When pigments are brought together in a certain combination there is very little variability in the inherent character of the resultant hue. In this case the original pigments in the paint sample were identified. Identical pigments were then procured and used to create paint in a sample range of ratio formulae, with appropriate solvents, additives and binders. These paint samples were then applied to a set of plates and each plate compared to the extant samples. None of them matched, either visually or by measurement. An identical set of plates was then subjected to artificially induced thermal ageing. After this process the thermally aged plates were compared to the extant samples and this time two of the plates were found to match to within an 80/20 tolerance, both visually and by measurement. The conclusion drawn was that the ratio formulae for the two plates and their pre-aged condition probably matched the ratio formulae of the paint originally applied to the airframe and possessed an exactly similar colour appearance. The most significant difference factor which emerged in this analysis was brightness  rather than hue or chroma. The difference in visual appearance was more significant than the difference in measured, colour science values.

Of course, this won't stop the arguments . . . 

With grateful thanks to Bob Alford for kindly making these artifacts available for detailed laboratory examination and analysis. (To be continued).

Image credits: Heading picture Punch magazine Feb 1860; Photographs of 5349 model and museum exhibit Owen Veal via Bob Alford; Intelligence reports courtesy Bob Alford; Artifact photos and rendered chips ©2010 "Straggler"


Anonymous said...

Thanks as always for the post. Something I found most distasteful (and ironic) in that aotake primered Zero thread was how the self fancied "experten" when it comes to German subjects, were mocking their counterparts whose expertise is in Japanese aviation. I suppose one could spend hours trying to figure out what drives people to be as such- but then again we all have better things to do with our time.

Thank you for providing a home for those of us who prefer a different approach....

James F. Lansdale said...

Nicely done Nick!

I hope you will also compare the colors as found on ReiSen relics which were removed from such crash sites within hours (PEARL HARBOR ReiSen 21) and a few weeks (BUNA ReiSen 32) after the crash. These pieces are still bright and shiny and have not weathered for many years! It would be interesting to compare the color shift on these pieces without the need to "buff back" any oxidation.

Also a comparison of the two different color as found on the metal surfaces compared to the color found on the fabric surfaces would be valuable since the paints used on these two surfaces were different as to the binder type used.

Keep up the great work!

Jim Lansdale

Arawasi said...

Thanks Nick. Interesting article. Occasionally too technical, though.
How big are the artifacts you have examined? Do you know which part of the plane are they from?

As for the request of our good friend Mr. Lansdale, I would assume that a serious researcher with a 40-year experience like him would have already done all the comparisons he mentions. If that's the case I would very much like to see the publication that has featured his research.

Joe Youngerman said...

Very informative as always. I was really turned off by that thread as well. The accused wrote a fairly "edgy" comment on my Claude some time ago but we had a good discussion off-line about it and other things. We didn't agree on everything but it was a good, civil discussion. I just hate seeing personal attacks...effective communication stops when that begins.

Mario Holly said...

Thanks for the very informative posting. I think I need to reconsider my fancy for RLM02 and start liking Tamiya XF-76 more! (ha-ha).
Since I triggered (unwillingly) that infamous "aotake primed Zero" thread I keep wondering what was so wrong with my "delivery". I re-read my own posting couple of times and besides little sarcasm at the end (about salt) I'm just not finding any sign of personal attack, trashing the model or anything else. Maybe you, or visitors here who read the thread, can help me to improve my "horrible communication/social skills"? And by the way I better turned the blind eye on aotake painted cockpit and landing gear (!), crooked landing gear and big gaps between wings and fuselage.
I cann't agree more with you that such a thread never evolved around Bf-109 matters. Interesting!