Aluminium forms an oxide on its surface when exposed to air. Aluminium Oxide. *
BUT* no frame is pure aluminium, it'll be one of various alloys.
I always fancied copper plating a steel frame. (Very easy to do with copper sulphate)) Which will turn green if you dont protect it from air/oxygen: ) But varnish it and it should be OK..... Maybe.
Aluminium forms an oxide on its surface when exposed to air. Aluminium Oxide. *
BUT* no frame is pure aluminium, it'll be one of various alloys.
I always fancied copper plating a steel frame. (Very easy to do with copper sulphate)) Which will turn green if you dont protect it from air/oxygen: ) But varnish it and it should be OK..... Maybe.