The shell is carefully removed from the polished mandrel by using differential thermal expansion. The apparatus is sited within a clean "tent" purged with dry nitrogen to ensure the newly minted reflecting surface is kept in pristine state. In this close-up it is just possible to see the inside of the lower part of the mirror shell, with its gold reflecting surface. The gold was first deposited on the mandrel, but now comes off onto the nickel shell, producing a highly polished surface with roughness comparable with that of the original mandrel (about 5Å r.m.s.). The mandrel is then cleaned before the next replication cycle.

Photo courtesy of MediaLario.