Yesterday evening the Tucson Astronomy Association had the monthly newsletter folding party. Dean Ketelsen, who works at the Mirror Laboratory, gave us a tour of this huge place.
I show a group picture. The mirror on the right was cast in a rotary furnace, and then allowed to cool very slowly, over a period of months. The destination for it is the National Observatory of Mexico at San Pedro Martir in Baja California.
The Lab is under the University Stadium bleachers.