yes, claims of painted frames as a general practice [all plants] need documentation that I've never seen offered other than the anecdotal "mine was"
but this pickling thing prompts some thoughts:
pickling various metals as a final manufacturing step is/was a universal practice, using different baths depending on the type of metal and intended use - I believe the frame components would have been treated with hydrochloric acid to remove the oxide scale, resulting in a layer of flash rust
GM trucks were consumer goods, made as cheaply as possible, but rust surfaced frames in the show room wouldn't be a big selling feature, so something would be worked out to deal with the result of the usual pickling process, and that 'something' needing to be as cheap as possible
painting directly over surface rust doesn't work well, and cleaning the surface, then priming and painting ain't cheap, but a quick
phosphoric acid dip would convert that iron oxide coat to a nice satin black phosphate coating requiring no further attention to provide an attractive "workman like" appearance for the first few months or even years -
it would look as if it had been painted, even if a few years of service subjected to road spray in a wet climate would have it back to the lightly rusted surface most of these frames are now - and any reference I've seen to a frame treatment calls it "chassis black" without the word
paint .... that's my take, and I really doubt anyone can make a better case for GM spending the extra dollars per vehicle to actually paint the frames
Bill
