Every two years, on average, the mirror in the telescope must be recoated so that its surface will be shiny. If not, it will oxidize and become blotchy, dimming the light coming into the cameras and limiting what the astronomers can do. The mirror is taken out of the telescope and lowered through an opening in the upper floor down to a tray, where chemicals are used to remove the old coating. A few grams of aluminum wire wrapped around heating coils on the right side of the chamber are rapidly heated such that they vaporize, sending a mist across the chamber that sticks to the mirror's surface and hardens.
Air is returned to the chamber, the surface inspected, and the mirror returned to the telescope.
The whole operation takes about three days. This chamber was also used for aluminizing mirrors in bomb sights during the Second World War.