No, there is no clear coating. It's bare metal that gets polished:
> The metallic fuselage skin of modern airplanes is made of alclad aluminum alloy.
The word “alclad” means a thin layer of pure aluminum is applied over the entire aluminum alloy fuselage skin, generally a variant of 2024 alloy, at manufacture.
This pure aluminum layer almost immediately turns into aluminum oxide: and then begins its magic.
A bit of polish applied periodically keeps the pure aluminum layer at a silver shine, otherwise it grows dull — but still continues to protect.
> Alclad has been most commonly present in certain elements of an aircraft, including the fuselage, structural members, skin, and cowls. The aluminium alloy that Alclad is derived from has become one of the most commonly used of all aluminium-based alloys. While unclad aluminium has also continued to be extensively used on modern aircraft, which has a lower weight than Alclad, it is more prone to corrosion; the alternating use of the two materials is often defined by the specific components or elements that are composed of them. In aviation-grade Alclad, the thickness of the outer cladding layer typically varies between 1% and 15% of the total thickness.
> The metallic fuselage skin of modern airplanes is made of alclad aluminum alloy.
The word “alclad” means a thin layer of pure aluminum is applied over the entire aluminum alloy fuselage skin, generally a variant of 2024 alloy, at manufacture.
This pure aluminum layer almost immediately turns into aluminum oxide: and then begins its magic.
A bit of polish applied periodically keeps the pure aluminum layer at a silver shine, otherwise it grows dull — but still continues to protect.
https://www.quora.com/Why-did-American-Airlines-stop-paintin...