Frederich, Tim on fri 19 jan 01
-----Original Message-----
From: Frederich, Tim
Sent: Wednesday, January 17, 2001 3:12 PM
To: 'Ceramic Arts Discussion List'
Subject: RE: quartz inversion and mold
Robin,
The quartz phase of silica has alpha quartz and beta quartz. Alpha quartz is
present below 1063 degrees F, the temperature at which quartz inversion
takes place. Any thing above this temperature is beta quartz. The difference
is in the bonding of the silica and oxygen. The bond changes at the point of
quartz inversion. It is usually reccomended to slow the firing down while
going through this point and most controller programs have this built in.
This inversion will continue to take place every time the quartz passes
through it as long as it is in a crystalline state. When the quartz becomes
part of the molten glaze or a glass form it is not crystalline any more and
is no longer subject to quartz inversion.
The reason that mold is said to add plasticity to a clay is that it helps
the flat platelets that clay consists of hold together. A plastic clay
always seems to stretch further and have better working strength. This is a
basic explanation and I hope it answers your questions.
Best regards,
Tim Frederich
-----Original Message-----
From: robin clifford [mailto:robinclifford@HOTMAIL.COM]
Sent: Tuesday, January 16, 2001 6:22 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: quartz inversion and mold
Hey, just wondering if anyone has some good information for me. It's my
first time teaching glaze calc and I was wondering if anyone knows of any
precice descriptions of what happens in quartz inversion. We've got the
basic alpha to beta crystals, but does there exisist a comprehensible
explanation of the how and why?
Also just wondering why mold is said to add plasticity to a claybody. Does
it just show that its well aged or is there something more to it? Please
respond to robinclifford@hotmail.com
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