Re: [ATM] convex secondary

[Ken Hunter <atm_ken_hunter@yahoo.com>]

In the old days, Pyrex blanks were moulded in forms
and were very full of in-homogenities and striations
(SP)? These could be easily seen on most any blank
from several y. Lately, I've not seen visible (by eye)
defects in the Pyrex disks that are currently
available. I would think that testing through the back
would be possible with today's glass.

Ken Hunter


--- Greg Jones <gregj888@comcast.net> wrote:
>  "Pyrex is not homogenous and has a lot of fine
> grain boundaries.."
> 
> I've read this in all the old texts too but am
> wondering if it's true (or still true).  Has anyone
> checked a Pyrex blank in the last 10 yrs?  Seems
> like to be low expansion it would need to be
> homogeneous, and how do you make it so it is not? 
> Has to be annealed too.  I'm not saying it's any
> better now than 40 yrs ago, just suspicious.
> 
> It's on my "to do list" to check, but still a ways
> from the top.
> 
> 
> Greg Jones
> http://home.comcast.net/~dac20/dac_001.htm
> 
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 


		
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