M Richens on mon 7 apr 97
In article <2.2.32.19970329182946.006f74e4@mail.lglobal.com>, Gavin
Stairs writes
Hi again Gavin,
brief Follow up.
The important thing about enamels being fully fritted is that all the
reactions, except the one with the body, have completed.
Using glazes with a lot of RAW you have to complete all the reactions
during the glaze fire. The trouble with cones is they operate on a
time/temperature combination. A fast High fire will slump the cone but
you won't necessarily have completed the proper glass formation, just a
skin of the most fluxable elements and therefore a lower chemical
resistance.
Max
--
Max Richens max@richens.demon.co.uk +44 (0) 1925756241
Enamel Consultant - Ceramist - Analyst programmer
Software for Batch Formulation and Millroom control.
Gavin Stairs on tue 8 apr 97
At 12:24 PM 07/04/97 EDT, Max Richens wrote:
....
>The important thing about enamels being fully fritted is that all the
>reactions, except the one with the body, have completed.
>Using glazes with a lot of RAW you have to complete all the reactions
>during the glaze fire. The trouble with cones is they operate on a
>time/temperature combination. A fast High fire will slump the cone but
>you won't necessarily have completed the proper glass formation, just a
>skin of the most fluxable elements and therefore a lower chemical
>resistance.
....
Yes, I've twigged that most glaze systems are far from equilibrium. It
would be surprising, after all, with the very viscous, or even refractory
"pure" materials about. Much easier with low fire glazes and enamels, or
with very highly fluxed crystallines and wood ash. And it must be the case
that many of the fine effects people strive for are in fact transient
conditions and gradients of one sort of another.
On a slightly different track... Do you know why the oxygen bond angle is
widened in siloxides? Seems most peculiar. And is it followed in the
Si-O-Al-O- of kaolin? Presumably. It would seem that this is a strained
bond, but that would weaken it. So perhaps some sort of hybrid, but I
don't see it.
Gavin
=================================
Gavin Stairs
http://isis.physics.utoronto.ca/
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