Previously shielded image intensifier faceplates have been manufactured by a method which has a number of disadvantages, requiring difficult and expensive machining, and introducing distortions.
These may be overcome by employing the invention, where a clear glass disc 13 and a black glass disc 14 are placed in a graphite mould 15 and located so that they fuse and form a block having a shape conforming to the internal configuration of the mould. Then the block need only be ground down to size and unwanted parts of the black glass removed.