[sibelius (Valerio)]

Hi everyone
I 'm thinking to make a new mirror for a new telescope and I am thinking to make it out of marble.
I have one question.
Let's suppose that I can get a parabolic surface for a fixed focal length that I previous decide and let's suppose that at this point I need to proceed to a fine grinding.

Now my question is, how can I proceed to fine grit to smooth the surface without loosing the surface shape?
I have already an idea but I would like to ear some other bell.

Thanks
V.