In a 6 Jan 2018 article at ieee.org, Celia Gorman reports on the casting
of the seven mirrors for the Giant Magellan Telescope (GMT) at the
University of Arizona.
The work takes decades and the first mirror was cast back in 2005.
Each mirror cost US$20 million and takes more than two years to make.
Story and video here :-
https://spectrum.ieee.org/video/aero...gest-telescope