Marty - 60's printing technology on offset presses would not have included metallic inks for the most part. So common practice would have to used the base of aluminum or gold foil and print black on top of it. The common issues with these types of printing jobs was either delamination of the ink from the metallic base, or scratching off of the printed top layer. I would think the base of those was originally a aluminum Mylar base as that was a common flexible base for tons of printing jobs including bumper stickers.