RE: ATM Pyrex glass questions

["Bertapelle, Ken" <Bertapelle.Ken@tci.com>]

Thanks to all who responded to this.  I've been calling suppliers to 
further research this question, and came across one that sounds
interesting.  If anyone can comment on this, I'd appreciate it.
Here's the story:

The company offers a competitive product to Pyrex, which they call
"Boro Float".  Both products have similar (low sensitivity) thermal
expansion properties.  Pryex is produced by "rolling", which has a
net effect of leaving more occlusions (bubbles) trapped within the 
material, and also a surface which is less flat (ripply).  Boro Float 
is produced by pouring the liquid material onto the surface of another, 
denser liquid.  The claim is that this produces a surface which is 
flatter, and an internal consistency which is freer of bubbles.  
It is also claimed that Boro Float is less expensive, although I 
don't yet have a price quote.  A down side is that the maximum 
thickness for Boro Float is 21 mm.

I asked the vendor to spec out a mirror blank with dimensions of
diameter = 20", and thickness = 2".  He is going to research the 
question of whether they can fuse several pieces to make up a 
thickness of 2".

My question is:  Does this sound like a good avenue to pursue?  Does
anyone have familiarity with this product that they can comment on
the correctness of the claims as to physical properties?  Does it 
seem likely that the process of fusing several pieces together would
upset the thermal insensitivity of the material?

Thanks.

- KenB

> -----Original Message-----
> From: Bertapelle, Ken 
> Sent: Tuesday, June 15, 1999 4:17 PM
> To: ATM
> Subject: ATM Pyrex glass questions
> 
> What kind of pyrex should one ask for when purchasing a pyrex 
> telescope
> blank?
<snip>