Colour Considerations ~ 9-shi Single-Seat Fighter (Mitsubishi Ka-14)

Some considerations pursuant to several queries about the colour of the Mitsubishi Ka-14 - 9-shi experimental single seat fighter (九試作単座戦闘機). Hitherto commonly depicted as natural metal (as in the first Fine Molds 'magazine issue' kit released with Model Graphix Issue # 350 in January 2014) but recently revised to become grey-green. Jiro Horikoshi described the Ka-14 prototype as being painted 'ash green' (grey-green):-

" . . . the skin had a quilted appearance caused by the unskillful application of the flush rivets. These dimples were especially noticeable in contrast to the rest of the shiny alumin surface. We solved the problem by filling the depressions with putty and painting the airframe with a thick coat of Navy specification ash green paint. Then the airframe was polished." *

Photographs of the aircraft do suggest a smooth finish but are somewhat ambiguous as to its very light looking colour. Japanese aviation researcher Mr Fumio Komine suggests from Mitsubishi records that the first and second machines were treated with polishing powder (磨き粉) to smooth the surface and then probably finished with grey-green paint, perhaps to J3 standard or similar (see discussion below). The original prototype had a black or blue-black painted cowling whereas the improved type had the new cowling painted in the airframe colour. Both had red painted tails. The tailfin fillet in the revised Fine Molds kit appears larger than in some representations depicting a much shallower and more subtle addition.

 Note dark painted wingtips

These details give rise to a number of questions. If at that time (1935) there existed an IJN specification ash green paint then why were subsequent production A5M delivered in natural metal finish? Up to about that time IJN biplane fighters (A2N) were reportedly finished in aluminium dope or camouflaged and most photographic images bear that out. However, a photograph** of a Saeki Ku A3N1 サヘ-191 (SaHe-191), manufactured by Nakajima in May 1936 is ambiguous. The wing, strut mounting and aileron connection rod of the aircraft in the foreground do not appear to be painted aluminium but rather in a pale, glossy paint and dope. With that in mind the two aircraft flying alongside could easily be envisaged to be finished in the same colour, a light non-metallic paint or dope rather than aluminium dope.

The first iteration of the IJN Provisional Standard (仮規格 - Kari Kikaku - abbr. Kariki) 117 for aircraft paint colours was dated 26 November 1938, three years after the Ka-14 was painted, which makes Horikoshi's reference to an 'IJN specification' paint puzzling. The most well known and publicised version of this document is the Air HQ (航空本部 Kôkû Honbu - abbr. KuHon) # 2943 Revision of 10 April 1942. It is possible that the IJN was already experimenting with or trialling grey paints before 1938 but the Army had standardised its own # 1 Hairyokushoku colour in 1922 with a revision in its application method from 1936 for aircraft such as the Ki-15. That is just after the testing of the Ka-14, but Mitsubishi were already applying paint to Army aircraft such as the Type 92 Reconnaissance aircraft (Mitsubishi 2MR8), presumably to the Army's # 1 specification, but again appearing very pale and 'bright' in photographs.  

Many Japanese reference sources and kits refer to the IJN paint colour as mei-kaishoku, mei-kai hakushoku or mei-hai-hakusho meaning light ash or light ash-white and one researcher*** has suggested that the colour was "IJA J1". It is unclear whether that was intended to mean the Army # 1 colour hairyokushoku (ash green colour) or the IJN Kariki 117 'J1' which was in a series simply called ash colour. The conflation of Army and Navy colours is long standing and even today some kit instructions suggest the Army # 1 colour for painting the A6M2. The colour J1 seems far too dark for the description light ash white, at least as it appears now, being similar to Munsell N4 (close to FS 26132) with a slight greenish undertone. The Kariki 117 J3 is close to FS 36307 in appearance.

 IJN J3 vs Army # 1

The Army colour seems much lighter and brighter on examples of the same vintage as the Ka-14, for example the experimental Ki-18 fighter (completed by Mitsubishi for the Army in August 1935), than on later Pacific War era aircraft. The Army Kôkaku 39 colour standard for # 1 is approximate to FS 26496 but a little darker, more greenish and saturated. It is also a little darker and more greenish than RAL 7032 Kieselgrau (Pebble grey). Confusion over this colour is also long standing as it has often been described on aircraft as blueish or blue-grey as well as greenish-grey. Those well-known colour photographic images of Toryu can easily be visualised as showing a blueish-grey but when the colour is closely analysed it proves to be close to the standard for # 1. Likewise the A6M has often been described and depicted as a distinctly light blue-grey colour.

FS 26496 

FS 26496 is a Munsell GY - Green Yellow and designated as Green Gray. Official pigments are Rutile Titanium Dioxide (white), Phthalocyanine Blue (Red Shade), Natural Raw Umber and Phthalocyanine Green (Yellow Shade). 

FS 36307

Interestingly the chip of this colour in a 1989 FS 565B fan deck now appears a slightly more blueish or neutral grey whereas the current appearance of the colour, now called Bulkhead Gray, is a definite Munsell GY - Green Yellow - a grey with a greenish-brown undertone. I have verified the colour values of FS 36307 across a number of sources, including the CIELAB D65/10 L*a*b* values reported in Aerospace Material Specification AMS-STD-595 of 02/17 and the spectrophotometer based colour measurements reported in Technical Report ARWSE-TR-17001 of the US Army Research, Development and Engineering Center of 10/17, all of which are consistent with the Munsell GY value. The official colour pigments for FS 36307 are Rutile Titanium Oxide (white), Phthalocyanine Green (Blue Shade), Natural Raw Umber and Carbon Black (Blue Shade). There is an odd optical effect at work here because when that old 1989 chip is visually compared to Methuen colours it still compares to the green rather than blue range of greys on the 1-2 scale. It has a very low and subtle colour saturation between blue and green.  

J3 and # 1 

The proximity of J3 and # 1 is borne out by the fact that when the Army and Navy colour standards were reconciled in the Aircraft Manufacturers 8609 document of February 1945 colour # 2-6 became the direct successor colour to J3 and was deemed similar to # 1. A swatch of 2-6 examined in 1975 was compared to Munsell 5 GY 6/1 and FS 36307. The closest FS value to 5 GY 6/1 is FS 16307 @ 2.07 (where < 2.0 = a close match). FS 16307 measures as Munsell 4 GY 6/0.8. 
 

* Eagles of Mitsubishi - The Story of the Zero Fighter' by Jiro Horikoshi (Orbis Publishing, 1982), p.21-22

** The Imperial Japanese Navy Fighter Group Photograph Collection (Kaiga Co. 2011), p.25

*** Out of Ameiro Cloud Into Hai-ryokushoku Sky by Yoshihito Kurosu (j-aircraft.com)    

Image Credits: Ka-14 box art © 2018 Fine Molds Corp.; Ka-14 photos via web; Colour chips © 2018 Aviation of Japan