The black is a phosphate coating, any other colors, greys, blacks reds etc are primers sprayed on in the paint booths
Mark. That's the first time I've heard phosphate mentioned for that.. Can you elaborate? was the entire body subjected to a phosphating process? or just some panels (like the floor) prior to assembly of the panels into the body? or? Any details you can provide based on fact, or conjecture based on evidences would be greatly appreciated.
The phosphate systems (both of them - Fisher's and Chevrolet's) are covered in some detail in the "First Generation Camaro Assembly Process" paper on this site, at:http://www.camaros.org/assemblyprocess.shtml#fisher
Here's an excerpt - go to the paper to read the details:
<<Fisher Body - Paint Shop Operations
The Paint Shop is broken down into phosphate, prime, sealing, and color departments; the body was suspended from an overhead conveyor with hooks at the firewall and at the ends of the rear frame rails through the phosphate system, and was transferred to a steel carrying truck before the prime system that carried it through the rest of the Paint Shop and through the Trim Shop.
Phosphate System: The raw body shell passed through a seven-stage phosphate system, where it went through a series of enclosed high-pressure hot spray stages where it was washed to remove all the oils and debris from stamping, welding, brazing, soldering, and grinding operations, then the body was coated with a hot iron phosphate solution which "etched" the metal and provided "teeth" for paint adhesion. The final stage was a de-ionized hot water rinse and blow-off, followed by a drying oven on the way to the prime booth.>>