Preparing the mandrel for the electroforming bath

The polished mandrel is suspended in its fixture ready for transport to the nickel electroforming bath. For the flight shells, the mandrel is first coated with the gold surface which will become the mirror reflection surface. In the electroform bath, a carefully controlled current defines the rate of nickel build up on the mandrel, ensuring minimisation of internal stresses. A horizontal black band is visible - this ring defines the end-plane of the mirror

Photo courtesy MediaLario.