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Ahhh. I cannot remember the name of the French artist who made a bunch of
sketches of industries right around the beginning or just before the
Industrial Rev. The mirror makers workshop is probably about as close to
what you're looking for. They were the glass grinders for centuries.

Diderot!! That's his name.

I imagine other then modifications for mechanization, the process would be
the same.
On Oct 14, 2013 10:39 AM, "Hall, Hayward" <[log in to unmask]> wrote:

>  Thanks Lief.  I'm not so much worried about the curve or sagitta as the
> precise focal point is marginally irrelevant in my case here.  I'm more
> concerned with how did they physically grind them.  DaVinci shows a several
> foot diameter grinding stone with a machine to work it across the surface.
> Curious if anyone has seen anything else.****
>
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>  ------------------------------
>
> *From:* Historical Recreation in the Kingdom of Calontir [
> [log in to unmask]] on behalf of David McNeal [
> [log in to unmask]]
> *Sent:* Sunday, October 13, 2013 10:38 PM
> *To:* [log in to unmask]
> *Subject:* Re: [CALONTIR] Grinding optics****
>
> Guillaume,****
>
> The measurement of determining the curve is called a diopter. I don't know
> the formula to determine the exact parabolic curve you may want, but Master
> Craig might be able to point you in the correct direction. Mundanely he is
> an Eye Doctor (I can't remember if he's an Optometrist, or an
> Ophthalmologist). He ought to know those formulae or be able to point you
> in the direction for them.****
>
> Lief****
>
> P.s. If nobody pipes up with his contact info, I think I know who might
> have it. PM me in that circumstance. Hope this helps.****
>
> On Oct 13, 2013 8:10 PM, "Hall, Hayward" <[log in to unmask]> 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.****
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> I'm currently employing techniques used by current Amateur Telescope
> Makers however, while primitive, I don't know their origin. ****
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> Thanks.****
>
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>
> Guillaume****
>
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