[R-390] What is on the 390 chassis anyway

[Scott Overstreet]

I don't know where all this zinc chromate stuff has come from. True, 
zinc chromate paint has been used for years and years on aircraft 
aluminum but I've never seen it on 390's.

The finish on 390 aluminum is "alodine" This is a very much still in 
use, aluminum finish that , believe it or not, is available in quart 
bottles in most automotive paint stores for a very affordable price----I 
can't remember just what I paid for the last bottle I bought. There is 
also "clear" alodine but this is not what you may want or was used on 
the 390's.

Commercially, the process is a dip in caustic (lye) to clean and etch a 
bit and then in a "bright dip" (?) to clean up the impurities left 
behind (usually a bit gray) and then into the alodine tank. The 
immersion period is usually about 45 seconds with fresh alodine and up 
to several minutes for near dead  alodine. The longer in the tank, the 
darker it gets which can be pretty dark brown. Ask Google for process 
details.

Alodine on a rag can make things look better but things have to be very 
clean for uniformity------wear rubber gloves, alodine stains.

Scott