The ceramic will then be removed from the mirror producing a light weight piece of glass from which the mirror will be ground. Side view of mirror blank showing the honeycombed effect when the ceramic molds have been removed from the glass of the mirror. These pieces of ceramic would be removed with the mirror standing on its edge. Imagine a multi-ton piece of glass standing on its side towering 8 meters above the worker. The structure is rotated slowly for the entire heating process and the liquefying glass fills the cracks within the structure.
Computers monitor the entire process which takes several weeks to heat, melt and cool.
The blue structures visible in this image hold the structure together as the glass expands with the heat. This is a nearly finished 8 meter primary mirror blank waiting to be ground and polished. The long process of grinding and polishing can take as long as 6 months. This is actually the bottom of the mirror. Close up detail showing the edge of the mirror's surface.