The 1951 MiG-9 maintenance manual ? Ремонт Самопета МиГ-9 ? may cast some light on the aircraft finishing practices of the VVS in the early fifties.
Page 226, the section titled РЕМОНТ ЛАКОКРАСОЧНОГО ПОКРЫТИЯ САМОЛЕТОВ, Подготовка лакокрасочных материалов перед их применением ( AIRCRAFT PAINTING DURING REPAIR, Preparation of paint before application - roughly the equivalent of the Section VII of the US Erection and Maintenance Manuals), states
Грунт 138А разжижается:
а) при нанесенни его непосредственно на металл ? разжижителем РДВ;
б) при нанесенни его на грунт АЛГ-1 или АЛГ-5-скипидаром или сольвентом .
This should roughly translate into
Liquid primer 138A:
a) When applied directly over the metal, use RDV thinner
b) When applied over primer?s ALG-1 or ALG-5, thin with turpentine or solvent
Thus it appears that the primer 138A, could not only be used as an alternative to the two zinc chromate primer's, but even be used in conjunction with them!
Page 227, section ПРАКТИЧЕСКИЕ МЕТОДЫ ОПРЕДЕЛЕНИЯ ЛАКОКРАСОЧНОГО, ПОКРЫТИЯ НА САМОЛЕТЕ (PAINT PRACTICES, AIRCRAFT FINISH) states
Проверить грунтовку покрытия. Окраска самолета нитроэмалями большей частью производится по грунту 138А коричневого цвета; масляные покрытия наносятся по грунту АЛГ-5 серо-зеленого цвeta или по грунту АЛГ-1 желтого цвeta.
This, in turn, should roughly translate into
Type of coating by primer type. Use aircraft nitro-enamel over brown primer 138A. Use oil-paint over grey-green primer ALG-5 or yellow primer ALG-1.
The above, along with the fact that both the primer 138A and the two ALG primer's are in the Albom Nakrasok, leads to the following considerations.
Primer 138A, specifically called liquid primer, must have been red-brown in color (it is called red primer 138A in an article in
Wunderwaffe) and somehow translucent, not unlike the
Prussian Blue Lionoil primer,used by the US aircraft industry (especially by Curtis) alongside the yellow and the green zinc chromate primers, or the
Aotake used by the Japanese aircraft industry.
Zinc chromate primer ALG-1, was greenish-yellow in color, not unlike the US zinc chromate primer, and its color variations were within the yellow-green range only.
The same applies to the ALG-5, given that it was a 50% mix of ALG-1 and grey A-14.
The wild variations in the color of the ALG-1 found in the aircraft wrecks - leaving aside the weathering and the state of preservation of said wrecks - may therefore be attributed to the application of one or more layers of primer 138A over the ALG-1.
My two cents only?
Best regards,
Pete57