1088629-A is referenced by 3 patents.
An optical element e.g. a mirror is formed by vapour depositing layers of alternately low and high index of refraction e.g. cryolite, MgF2 or SiO2, and ZnS or TiO on a curved glass substrate in an atmosphere of neon, xenon, krypton, argon or radon, and then heating at, e.g. 400 DEG C. The glass cups 1 are first cleaned by a glow discharge and the material is vapour deposited alternately from crucibles 4, 5, whilst a holder supporting the cups is continually rotated by a wheel 14. The process is controlled by a photo-electric cell 17.