Gold leaf is very very thin and much less expensive than you might think. I don't have any personal knowledge of the chip-maker's process but it is very possible that gold leaf rather than the currently used 'gold colored' foil on plastic was used in the early days. This would be even more likely if you consider that gold was only $35 an ounce back in the sixties and earlier. This could explain how some of the old hotstamp chips from the early days look so bright today. There's no way that 24k gold could age to silver.

There was once more pride in product that there is today with the hot-stamp chip makers.