- Lime glass CTE: 9-10 PPM per Degre C - Build from a 5 mm sheet of glass - Cooling time 10 to 15 time faster - It will require a 6 - 9 - 18 points mirror cell - Back face curved convex - Back face a bit wavy, result of the fusing process - Expected mirror figure change during cooling : 1/13 wave per degre C.
The back face is a bit wavy. To achieve a good fusion of glass, it must be at the required temperature. But at that temperature the glass flow under it's own weight. So beware, in sandwich format, that are totally flat and said to be fused. For the figure change, since the frontal layer of glass is 5 mm thick, the rate of cooling will be very fast and within a few deg C of equilibrium, a very low figure change is what you should experience. On a differential of temperature higher then 5 deg C, the segments will strart to exchange heat and a print-through figure will appear on the parabola. The accurate figure will re-appeared at the rear 5 deg C cooling threshold.