The field of optical studies at high pressures has been limited to a range of a few thousand atmospheres not because glass would not withstand a higher pressure but because the proper window support had not been used in order to utilize the maximum strength of the glass.
Proceedings of the Iowa Academy of Science
©1930 Iowa Academy of Science, Inc.
Wilson, Robert and Poulter, Thos. C.
"Some Recent Developments in High Pressure Windows,"
Proceedings of the Iowa Academy of Science, 37(1), 299-302.
Available at: https://scholarworks.uni.edu/pias/vol37/iss1/72