Does anyone have references to period grinding of optical glass or metal, specifically concave mirrors.  I've see DaVinci's grinding machine (too difficult to produce), various post-period techniques, and sphere production for eyeglasses, but nothing really relating to the large concave "burning mirrors" described both in antiquity and in late period.  Birringuccio talks about casting them but really doesnt go into how to produce the parabola.

I'm currently employing techniques used by current Amateur Telescope Makers however, while primitive, I don't know their origin.