“Next came an incredibly thin layer of silver weighing only 64 grams spread over the 8.4-meter mirror.”
The Rubin primary/tertiary mirror took seven years to make. The silver that turns it from glass into a mirror weighs 64 grams and went on in 4.5 hours inside a 128-ton coating chamber. The hard part is a protective layer thick enough to survive cleaning and thin enough not to eat photons. Seven years of glass, and the science rides on 64 grams of silver and a coat thin enough to wipe.