Thursday 19 October 2023

Japan Aircraft Standard 8609: Aircraft Paints, Standards by Colour of Feb 1945; Part 1

On 5 February 1945, following a review exercise by the Aviation Industry Association's (AIA) 6th Sub-Committee of the 2nd Chemical Industry Association a new single National Aircraft Standards was issued entitled ‘Japan Aircraft Standard 8609: Aircraft Paints, Standards by Color’. The AIA was a cooperative body of the Ministry of Munitions Air Weapons General Bureau formed in January 1944. This achieved a reduction from the 54 colours in the IJN Kariki 117 (revised) of April 1942 and the more than 40 colours in the Army Aircraft Materials Standard No.39 of 1935 down to 26 colours with some compromise. For example the Army # 27 Ao Midori iro - 青緑色 (Blue Green colour) was succeeded by the similar IJN D2 which was re-designated as 1-2. Colour D1 was not represented in the revised  system and it is apparent that by that time a dark green colour closer to D2 in appearance was being applied as the standard IJN upper surface colour. In the new numbering system the prefix indicated the hue and the suffix the specific colour value within that group, with greens represented by colour swatches 1-1 to 1-5 and greys by colour swatches 2-1 to 2-7. In each case the new colours were designated either as direct successors to the previous colours, and identical to them, or as being similar to them, and presumably acceptable as alternatives. The original colour swatches in the 8609 standard are 14.4 cm x 9.1 cm in size.

The respected Japanese researcher and film director Sunao Katabuchi has asserted (in Scale Aviation magazine, February 2021) that D2 was adopted by the IJN in November 1941 for the camouflage of aircraft flying over the ocean and in the later phase of the war was applied to the upper surfaces of almost all IJN aircraft including Zeros and trainers. However according to Yoshihito Kurosu: 'the 'Hiko-ki Keikaku You-ryou-sho Kaitei-an' (Proposal for the revisions of aircraft planning procedures) issued by Navy Air Command HQ in March 1944 has a table of standard colors and codes under "Kari- kikaku 117 Shiki-betsu Hyojun" (Provisional Standard 117 Color Norms). The table specified the upper-surface color as D1 'an-ryokushoku' (暗緑色 - dark green).

The official name for D1 was 'Deep Green Black' and not 'dark green' but the inconsistency of colour terminology in official Japanese documents, both IJA and IJN , is typical and can present ambiguity. D1 was not included in the 8609 colour standard of Feb 1945 but only D2 (becoming 1-2), which tends to lend credence to Katabuchi-san's assertion.

This year the Japanese Aeronautic Association Aviation Heritage Archive published a most magnificent book on the recent Kawasaki Ki-61-II restoration with amongst its many superlatively documented and presented details of the airframe and engine includes actual spectrophotometer measured L*a*b* values of the 8609 Standard colour swatches reported for the first time, and full size representations of the swatches. They include 1-2 the successor colour to the IJN's D2 and 2-6 the successor colour to their J3 (and reported to be identical). Those important measurements have now been converted to sRGB with the rendered swatches presented below. The swatches have probably become slightly darker and more brownish due to being stored out of light for over 70 years but as shown they are the most authentic and accurate reproductions of the actual 8609 swatches compared to many misleading photo comparisons and facsimiles in magazines, etc. Whether the J3 colour was deliberately made dark to allow for the inevitable chalking* and lightening of the paint surface is moot. But do please note that the 1942 0266 report on camouflage trials conducted at Yokosuka described the then currently applied Zero colour as 'J3 Haiiro (飴色 - ash colour, grey) leaning slightly towards Ameiro' (飴色 - amber, yellowish-brown). Other 8609 colour swatches will be analysed and presented here in due course. A full verification and comparison exercise to other colour standards, including Munsell, has not yet been completed due to personal circumstances.

The current 'go to' fad of using Gunze Mr Color 35 to represent 2-6/J3 is misleading. A better match is to use Mr Color 70 RLM 02, perhaps lightened a little.

One important point to bear in mind is the difference between a colour standard, representing the hue  as authorised, and the actual applied paints which could and did vary for many reasons, both as applied and from subsequent exposure and other cinditions in service. Also it is improbable that the swatches, intended simply to show colour, were created with the same pigments and components of the actual paint coatings applied to aircraft by manufacturing companies such as Mitsubishi, where protection and serviceability would be considerations beyond just colour hue. Another point to make is that the subject has long been clouded by an equivalence made between subjective opinion versus objective scientific facts and data. The resistance to the latter by the former, often driven by presumption and preference, is effectively impossible to overcome.  

In ‘chalking’ the polymer of the paint is eroded and a powdery patina appears over the surface. Where the white pigment titanium dioxide is present in the paint (in rutile form) as with the Zero the condition is usually exacerbated. “The photochemically active titanium dioxide is both a UV-activated oxidation catalyst and a UV absorber. Free radicals are formed at the surface of the titanium dioxide and these then oxidise the (paint) binder by photocatalytic degradation. This reduces the gloss and produces a friable layer on the surface of the paint film - the process called ‘chalking’.” - The Chemistry and Physics of Coatings, A J Marrion, Royal Society of Chemistry 2004. The effects of chalking, very prevalent in coatings exposed to persistent high temperatures and humidity as well as sunlight are often confused with the fading of colour pigments, an entirely separate process. 

 Image credit: Schematic © 2023 Aviation of Japan


WK said...

Hi Nick, could you elaborate more on "it is apparent that by that time a dark green colour closer to D2 in appearance was being applied as the standard IJN upper surface colour." I've always assumed D1, or whatever Nakajima painted their planes, whether it was D1 or a variation of D2, was used till the end of the war.

I'm looking forward to more installments in this series Thanks


WD said...

Yes, do please elaborate on this for us.
This is a wonderful post Nick!

Straggler 脱走兵 said...

Thanks for your comments Woody and WK. The lack of response to this blog article suggests many might prefer glossy books with misleading photographs so I might not spend the time to continue this exploration! For example the current 'go to' Japanese fad for Gunze H35 to represent J3, taken up in the West in the belief that any colour information from Japan must be gospel, ignores the fact that it is a warm grey and not a light, bright, blueish grey, even before a slight leaning towards ameiro is considered. And H35 is not even the 'neutral gray' beloved of that fad. It is a Munsell Blue.

As for D2 In addition to Katabuchi-san’s credible assertion about it the paint on Raiden artefacts is closer to D2, the Kyushu Hikoki company paint procurement records of 12 May 1944 for manufacture of the Q1W Tokai anti-submarine aircraft also mention only D2 - (p.116-117 of ‘Japanese Anti-submarine Aircraft in the Pacific War’ by Ryusuke Ishiguro and Tadeusz Januszewsk, MMP Books 2018). Also there is Robert C Mikesh’s examination and measurement of extant paint on NASM aircraft reported in the Asahi Journal many moons ago. That was presented in Munsell values but related to Thorpe’s table of colours. The majority of paints were deemed close to N2 but the Nakajima aircraft - A6M7, B6N2 and J1N1-S were all closer to N1. N1 correlates to both D1 and D2 quite acceptably but N2 is closer to a faded or chalked D2.

Given weathering of the paint surfaces the difference between D1 and D2 on a model is probably academic, with the real issue for modeller’s being the difficulty of scaling such dark and saturated black green colours convincingly. The bright, light greens often seen are not very representative of the majority of real paint.


Michael Thurow said...

I'm very sorry that I haven't responded in time, Nick, and that you come to such conclusion. A typical response to this type of blog, which are actually the ones I appreciate the most, like "great" and "most helpful" appears a bit trivial. But such information IS most helpful. If I weren't in the middle of my home move I would have already copied it into my private archive of Japanese colour data.
Thank you for your work, and please carry on. There was no colour update for quite a while.

Sincerely, Michael

Straggler 脱走兵 said...

Thanks Michael! ;-)

Dan Salamone said...

Hi Nick, I echo Michael's thoughts on this type of post. I have been quite busy with work, and just saw this today. Your thorough description and process is indeed appreciated!


Alex said...

Very interesting and important research for subject. As usual. Great thanks.
Will it be correct for modellers to use for IJN planes only D2 color?

Anonymous said...

Hello Nick,
I bought the book during a work trip to Japan a few weeks ago and was happy to see the info contained there and a bit confused as they used another colorimetric space with which I am unfamiliar. Your article is great and sloved the issue. I really hope you follow up on it and be reassured that, even if mostly silent, you have a following.

Thanks in any case for your excellent work


Straggler 脱走兵 said...

Thanks Dan. Alex and Carlo. Alex I'd use D2 as a guide but it does appear that the Nakajima applied green was darker and closer to D1. The Munsell measurement given for the NASM B6N2, for example, was not consistent with the N2 cited, being closer to D1 and towards FS 14077. Mikesh reported the G4M3 as (Thorpe) N2 overpainted with N1. Really I think you must choose dependent on your preferred paints and consider it a personal interpretation. Please note especially my comment about paint colour standards versus applied paints. There is leeway for variance.


Anonymous said...

Keep 'em coming Nick. So many more of us follow these types of articles than you know, we just don't comment.

Wind Swords

blitzkrieg_bop said...

As usual very interesting and useful post, thanks for your research efforts,Nick.

Claudio Moura said...


very thanks for your consideration about this so polemic and difficult topic!!! I hope your second part. ;-)

Have a nice week.

WD said...

Nick, I posted a link to this blog post on an interest group on Facebook, and it got a LOT of attention, so the interest by modelers is out there, I just think quite a few don't mention it.

Mark Smith said...

Thanks for this, Nick, very interesting how the ‘word’ from Japan in recent years is a return to ‘neutral greys’ for overall schemes / undersides of aircraft (even when certain model paints prescribed don’t qualify for the term). And can you share info about the availability of the Ki-61-II restoration book?

One immediate thought I had right after reading: imagine coming to this post as a newbie! It can still be confusing for one who has followed the subject for decades. One thing that would lend larger context, not just to newcomers but for me, is to go back to the guy who was the ‘starting point’ for many of us in the, uh, older demographic, Don Thorpe. His work was respected from the start in Japan and elsewhere because he obviously had some great sources. His two books by Aero Publishing covering IJN and IJAAF colors and markings books, with their printed color charts and with occasional quotes from Japanese wartime directives for paint finishes, hinted at these sources but particularities were largely lacking. They are remarkable books to have withstood sixty years of changing paradigms; but their absence of any critical apparatus, even a simple bibliography of primary sources, means that I grew up wondering exactly how, and by what, Thorpe was informed, to present such an arcane subject insulated by a significant language barrier with such confidence.
Here I’m not speaking of individuals, but sources such as Kariki 117 and JAS 8609. Did he have access to these (whether or not they were known as such then)? What were his sources in the mid and late sixties; and who allowed him introduction and access to them?

**In no way am I undermining Mr. Thorpe, his research, or his books. Anyone interested in our subject is in Don’s debt.** But I wondered about these things when I was seventeen. I’ll be seventy next year and would still like to know. And knowing might help me make some connections with the ongoing discussion. Thanks.

Straggler 脱走兵 said...

Hi Mark

Not really a 'return' to neutral greys as the 'word from Japan is still essentially the old 明灰白色 - mei hai (or kai) haku shoku - light/bright grey(ish) white colour, with an insistence on black and white pigments only which is not borne out by examination of the 8609 swatch or the various widely examined extant examples of paint by authorities such as the late Jim Lansdale and several others. Instead warm, yellowish greys, very similar to RLM 02 and RAF Camouflage Beige (Hemp) in character but which chalk with exposure to lighter and more greyish greys. The Gunze Mr Color No.35 fad which is supposed to represent this surprisingly light and bright 'neutral' grey 'word' actually measures as a Munsell B - blue. It is a bright blue grey, so although it looks attractive on Zero models I'm afraid that the 'word' from Japan is largely bunkum in terms of actual colour science and factual data. On the other hand the Aviation Heritage Archive book is the first serious attempt to actually measure with spectrophotometer and record in L*a*b* the colour values of the extant 8609 swatches in Japan. And the results fly in the face of recent glossy presentations and propositions.

As to Thorpe's approach to cataloguing the colours, he explained it in a letter to the British PAM News magazine in 1979 and I touched on it briefly in the Painting the Early Zero-Sen PDF. In 1975 the then editor of the Koku-Fan magazine Mr Toda sent facsimile swatches from 8609 to researchers in the USA (per the note on the schematic included in the blog above). I'll expand on Thorpe and post both the letter and accompanying table on the blog which might hopefully lay a few ghosts. Thorpe suggested his N10 Light Grey for the Zero colour, approximately similar to FS 26493 and a Munsell 'neutral' N 7.5/0, but his N9 Medium Grey was/is closer to the actual colour, a Munsell 10 Y (Yellow!) 5/1, a warm grey slightly lighter and greyer than its closest FS/AS value of 34201.

One of the ongoing problems is the subtlety of the colour and that so many seem unable to get their heads round the slippery and 'warm' nature of the grey and elusive greenish undertone involved. But that also pertains to the understanding of RLM 02, too often represented as a 'cool' grey green.