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3 - In the beginning I was searching for a glass blank but I had some trouble find one of the size 16inches and then I was thinking of the problem of aluminizing the final product.
Why would you think that aluminizing marble will be easier than glass?
Before you start, make sure you find an optical coater who is willing to aluminise a marble substrate for you. Make sure you get overcoating because you may never be able to re-coat the mirror. Old coatings are removed with highly corrosive liquids some of which are acidic and that will dissolve the optical surface.
I was looking also at the refractive index of a general glass and marble and I would say that in a "good range" of wave lenght are comparable.
Light does not pass through a mirror so the refractive index of the material is irrelevant.
So what I have is basically this piece of marble of 495x403x30mm that I am planning to machine with my cnc.
I machine many piece of marble doing relief and incision and never had problems so I am thinking to have a go.
I am still thinking as I will proceed to smooth the surface to the final result.
You can probably chomp out the surface to make the two curves. CNC machining is only any good for very coarse machining, it isn't nearly an accurate enough machining method for something like this.
Depending upon the quality / grade of CNC machine you have, you need a surface accuracy 1000-10000 times more accurate than a CNC can provide.
You will still need another piece of marble to use as a tool to grind and polish the surface in the conventional way.
Good luck
Joe
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