glass to check for cracks and such and one thing I notice alot in older hot stamps is tarnishing. I cannot say for certain whether or not yours is, in fact, tarnish, but if I had to make a judgement based on these scans I would say it is. The zero on the chip to the left and inconsistency throughout the color of the letters would be an indicator.

This is only a guess on my part, though.

Here is one of my chips which shows why I believe it is tarnish. Hope this helps