Re: [ATM] Worm track update

["Thomas Janstrom" <thomas@moiler.com>]

Hi Dale,

In that case they are "feathers" these are indeed from the casting of the
blank, they are minute swirls of either furnace dust, glass pouring ladle
primer (similar to kiln shelf primer) or entrained mold release (kiln shelf
primer). So long as they are not huge and very dense (optically speaking)
they won't be problem, just a bit unsightly. Striae are a bigger problem as
they a change in the homogeneity of the glass itself and so they affect the
local COE and so can cause stress related issues.

Thomas. 
"I cast glass, either hot or cold!"

-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Dale Eason
Sent: Saturday, 2 June 2007 11:25 AM
To: atm@atmlist.net
Subject: [ATM] Worm track update

I looked at the 10 f5 60 year old uncoated Pyrex
mirror under different lighting conditions last night
when I took it back to the makers shop.  I could see
what looked just like a worm track but it was inside
the glass.  It did not show up in the Foucault image. 
So now with that info and the interferometry info I
believe the worm tracks are structures in the glass
that the grinding and polishing carved down into. 
Probably no amount of polishing will remove them. 
They are caused by the way the Pyrex was poured into
the mold.



Dale Eason


 
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