For the spanish type 5 un 1937 I decided to paint interior in A-14 as say KL
The second plane is a type 10 in 1938 in China.
The interior AII blue as we can see in the I-16 Type 5 preserved at Chkalov Museum, have been repeinted after june of 1940.
I propose that if after 40, interior color is the same that the downside part of the plane (AII blue) it could have been the same thing before 1940.
Do you agree with that choise ?
Maslov (most likely based on technical manuals) says that: "in the beginning interior was painted with gray oil paint. After February 1939, in order to improve moisture resistance, fuselage interior was primed with yellow ALG-2 primer and then painted with AE-9.
From this we may conclude that interiors were primarily painted to prevent wood rotting - that is why they used oil paints, not nitro paints (AII paints were never used to protect wood...). In the beginning they used cheaper A-14 and from Feb 1939, better quality and more expensive light gray AE-9 & ALG-2 primer.