Thank You guys. And again for Rich, as it is not the first time You are helpful.
One more question. Am I right to assume the differencies of the fuselage panel shades seen on P-51 pictures of WWII era come as a result of light reflexing on aluminum alloy sheets? These would be coused by, let's say: different directions of final finishing of the tin, different direction of reflexies, different care taken by crews and so on, but not by different alloy types. Right?
There are some different alloys used on the wing fairings. There are also different directions the grain of the skins run. There are also differences in the heat treat on the skins that require deep forming of compound curves, such as the curved skins just aft of the canopy.
Certain areas have an acid cleaning done where spot welds are performed.
These are usually the differences you see in wartime photos of newer A/C.
After months of use the metal dulls a bit from oxidation and exhaust depending on where it is in service.