Re: [ATM] Clay based mirrors from dental material

["Geoff Nelson" <gjnelson@absamail.co.za>]

My wife is studying dental technology at the moment. Give it another 
two years and she will have completed the course. I will then 
hopefully be able to confirm this idea with some practical 
experience.

Just some comments on shrinkage (term she uses for change in size 
after firing or casting of metals) There are tables distributed with 
all the materials so that you can compensate for the shrinkage in the 
alloy that you are casting by changing some parameters in the casting 
material. It should be possible to calculate what ratios of shrinkage 
there are and design for the end result that is needed.

Personally I think the final result is very dependent on the 
thickness of the glaze and how much you will be able to polish before 
you go through to the clay support. In principle I think it will be 
possible and may have benefits for the final product. Costs may not 
be less than or manufacture easier than glass.

Geoff

> Schott's data site shows that there are dental materials available for
> use on both the core mirror blank and the glass coating. Both appear
> to exibit almost zero thermal expansion when cured. I did not dig
> deeper into the process other than to find that their glaze for
> porceline dentures requires only 800 degrees.to fire it 
> 
> That's comparatively cool relative to the temps needed to melt or
> "slump" Pyrex  and well within the reach of amature telescope makers
> with a backyard kiln.
> 
> I've yet to explore the actual material from which the porceline tooth
> is made. I seriously doubt it shrinks much if at all OR, it's possible
> that they make the replacement larger so it fits right after it
> shrinks. I don't know.

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