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I don't have that Detrot (mentioned by Mc Neal above.

On 10/13/2013 8:10 PM, Hall, Hayward wrote:
> 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.
>
> Thanks.
>
> Guillaume
>