Re: [ATM] Worm track update

[Dale Eason <atmpob@yahoo.com>]

I think they are Striae.  They look just like what
happens when you pour a viscus liquid into a pan and
some look like frozen stir marks inside the glass. 
They do not look like foreign material in the glass
but look like different densities of the glass.  The
ones I call worm tracks are gutter shaped.  Steep
sides with flat valley floors. These usually have one
right angle turn in them and are comma shaped . There
are several in the Foucault image.

Dale Eason
 
--- Thomas Janstrom <thomas@moiler.com> wrote:

> 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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