Getting ready for coating

Technicians at ESO’s Paranal Observatory, Chile, watch a mirror segment of the Extremely Large Telescope (ELT) be carefully lowered into a protective box for coating. This includes silver for reflectivity, and nickel chromium and silicon nitride to improve adhesion and prevent tarnishing. Each of the 798 segments that will make up the ELT’s primary mirror will need to be coated, as well as 133 extras, so that segments can be seamlessly removed for frequent re-coating.