An Aluminization

The process of applying the reflective coating to the objective mirror in the reflectors. This is best done under very clean conditions and under close to vacuum conditions, to avoid impurities on the surface. The chamber in which this is done is called an aluminization chamber. Typically the effects of dust and oxidation result in telescopes needing a new coating every few years. So, large telescopes generally have aluminizing chambers near the telescope.