My daughter sent some pictures from a recent tour of the Steward Observatory Mirror Lab at University of Arizona where she is a graduate student. The ease that we can take and send pictures now makes it so much easier to share experiences across distances.
The picture at the left has some orange stairs toward the right of mirror being constructed; they give some concept of the scale of the place. These are large mirrors! The mirrors are made of borosilicate glass - which is what Pyrex used to be before the 1980s. At the very last their reflective surface will be coated with aluminum.
See the slide show below for other pictures of the lab.