Massimo,
For TsKB-54-1 you have
All surfaces were unpainted metal...
More preciselly, this is an example for
anodized dur-aluminium exterior. Unpainted anodized dur-aluminium is also mentioned in SB link - it was actually against 1937 regulations, so very rarely seen on operational planes.
For TsKB-54-2 you have
This aircraft was painted of
silver dope.
In 1939 it was probably painted in silver AE-8.
AE-8 is enamel paint, not a dope! Nitro -cellulose AIN was a clear dope.
Dope definition from
http://www.thefreedictionary.com/dopeA type of lacquer formerly used to protect, waterproof, and tauten the cloth surfaces of airplane wings.
Dope impregnates fabric, paint forms a layer...
HTH,
KL