Let me tell you . . . this shot at full resolution takes my breath away (I have a 30 inch screen).
This is my best effort to date at blended layers. Try at least the X3 view, but if you can, click on the "O" for original.
Early 1900s binocularsOld Binocularsgrandfather's binocularsBlended Layers example
I would imagine it's glass, but don't know for sure. Glass is very stable, and hence why I was surprised.
. . . and I never did more research after I write this. One of them "when I have time" things . . .
I have seen this crystal pattern in old lens before but I do not know why it occurs. I think it is a crystal or mineral growing in the lens..do you know is it glass or cut crystal for the lens?