Composite Optics. NASA old stock. Not sure exactly what this is. Please help identify. 3.965 Lbs. same glass that the Hubble telescope was made from. I do know it’s Corning ULE ultra low expansion glass. I believe it is 7972 . I have multiple pieces in various sizes and weights. Please email with questions or comments.

Thanks,

Mark

From the internet…

Corning® ULE® Glass (Ultra-Low Expansion Glass) 7972 is a titania-silicate glass with near zero expansion characteristics that have made it the material of choice in unique applications such as machine tool reference blocks, gratings, reference blocks, interferometer reference mirrors, to telescope mirrors.