Casting a lightweight hexagon back glass telesope mirror

This video shows nearly all the steps in the process of casting an experimental lightweight glass telescope mirror. It starts with a CNC cut foam positive mold, which is used to make a plaster negative mold. The plaster mold is used to cast a positive in glass in a kiln. Then a sheet of glass is fused on top to be the surface to be ground and polished. You can find out more about this project at