I have started grinding of the mirror, but the tool have problems. The concrete dissolve under the grindingprocess, the consume of grinding powder went to heavy and the mirror-grinding don’t succeed. I will make a new tool, in iron I have made a 2 mm sheet which will be mounted upon the concrete.
The mirror is grinding on a block of concrete, other ATM’s use stone, piece of iron bar, plate glass or something else wich is more hard than the pyrex glass.
After four hours grinding sagitta (the hollowing) is 0.9 mm, it shall be 2.9 mm.
This new tool will be casted into the concrete. And then it will be easy to hollow out material from the plate glass.