Re: ATM making a different kind of mirror

[The Silent Observer <silent1@ix.netcom.com>]

Ina Ron Lippard Renaissance Reproductions wrote:
> 
>     Let me begin by saying my clientele is shall we say a bit on the
> interesting side.
> I have a contract to make a mirror out of Labradorite. It must be polished
> with a slight
> dish to it. I'd say the Sag should be about 1/16" at the center.The shape
> of the piece
> may be round or irregular, since it will have been cut from a rough rock.
> My expertise in
> optics is just enough to get me in trouble. The client wants this to be a
> 'gazing glass'.
> So what is the most straight-forward way of generating a spherical mirror
> on a rotating
> lap? I want a polish you can easily see yourself in. The material will be a
> highly colored
> Labradorite that is about #6 on the Mohs scale. I will be filling any
> cracks or holes with a
> water clear epoxy. Any help is most grateful.
> regards, Ron

I've got no expertise in polishing minerals, but at Mohs 6, it should
grind very much like glass or quartz.  The same techniques that get you
from roughly flat to spherical and polished should work, and in this
case you don't particularly care if the irregular edge gets turned a
bit.

In general, if working with the material on the spindle, you just need
to grind the center a bit more than the edge and keep the work
randomized.

-- 
It is well to approach all wonders and miracles by gradual stages or
degrees . . .
                                                           Fritz Leiber

Donald Qualls, aka The Silent Observer           NAR # 70141-SR Insured
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Opinions expressed are my own -- take them for what they're worth
and don't expect them to be perfect.