[ATM] Clay based mirrors from dental material

[artbianconi@blast.net]

Richard, I've no experience in pottery making and, as I indicated, this is 
merely an intellectual exercise that is not likely to get explored for a 
while given current interests and commitments.

Yes pottery clay does exibit a lot of shrinkage. I only used that as an 
example of the methodology because it's a process many have some 
awareness of. 

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.

A friend of mine is an Dentist and teaches at Penn State's College of 
Dentistry. I've copied him this post. I will ask him to give me a crash 
course in the materials and processes dental labs use to make prostetic 
devices.
An astronomical mirror, made from a material like fine china or similar 
vitreous material and glazed would not be breaking any new ground. It 
would simply be cross transfer of existing technology.
I may be on to something here.
Wouldn't it be funny:
For decades we have been using dental plaster for making the tools we 
grind glass with. It would be a hoot if we discovered that a viable 
alternative to heavy and expensive Pyrex blanks were also to be found in 
the dental lab.
Art

On 13 May 2004 at 4:22, Richard Schwartz wrote:

In my early attempts at mirror technology,  I tried to make clay 
grinding tools. This is not as easy as it seems. When the clay 
dries, it shrinks up to 15%.    If you are extremely lucky, it does 
not crack, and you get to fire it.   Then it shrinks another 10%.   
The shrinkage prevents you from having accurate dimensions.   
Based on my limited experience, I am not optimistic on
this one.

... Richard

> [Original Message]
> From: <artbianconi@blast.net>
> To: <richas@earthlink.net>
> Date: 5/12/2004 5:46:55 AM
> Subject: Alternate Mirror Blank materials

> I started a conversation at the STAR astronomy web site that is very
> much up your alley.
>
> It's speculation about one day being able to bake a clay based
> mirror blank in your oven at home, glazing it and figuring per
> normal.
>
> http://www.starastronomy.org
>
> Art


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