Ron Roy on fri 15 feb 02
I have several papers on bubbles in glazes - which I have not been able to
work on - some are in French and even though I have had help with those I
still cannot deem to really get the specifics.
Two factors I do know about -
1. Alumina will help keep the bubbles smaller because it reduces viscosity.
2. Unmelted silica particles will anchor bubbles - preventing them from
getting out.
I have done some experiments along those lines but have not been able to
get any observable results. I don't know how important they are either.
Some bubbles are thought to be water - some CO2 and I'm sure there are
other kinds - Tough problem I think - especially at cone 6 were boron -
because it melts so soon can add to the trapping.
As for the crazing - if those edges are raised - body compressing the glaze
- that either means it is the opposite problem to crazing - a low expansion
glaze - or maybe brought on by cristobalite which inverts around 200C -
could also be the lithium effect seen sometimes in glazes with more than a
little lithium Carb.
Or maybe those cracks just look that way.
The only way I know how to see what is really happening is to measure the
body and the glaze separately with a dilatometer and compare the charts.
RR
>Dear Jim.
>
>I did send a copy to Ivor at iandol@tell.net.au. Hope he gets it.
>
>You mentioned about your microscopic observations on "Bubbles". What is
>your scope objectives' magnifications?
>When I was looking at crazed areasof pots under my 'scope, which is 30X, the
>crazing lines were bulged up, as if the glaze was once crazed, but later it
>tried to smooth out and couldn't for some reason. Of all the crazing lines
>I looked at, there was no exception. Can you explain this phenomenon?
>
>Mariko Cruse
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
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Margaret Barlow on wed 20 feb 02
>1. Alumina will help keep the bubbles smaller because it reduces viscosity.
>
I am trying to understand this. I am sure you meant that Alumina increases
the viscosity. So I am assuming that because of the increase in viscosity
it is more difficult for the bubbles to expand as the pressure exerted on
them would be greater in a glaze of high viscosity than in one of low
viscosity. does this make sense? Is this in fact what you are saying?
Margaret
Ababi on wed 20 feb 02
I think it is all wrong.
If use alumina oxide to make a glaze matte, I shall get the glaze
matter, dryer.
If I use Alumina Hydrate, in the some molecular parts, I will get it
matte too. But: The Hydrogen bubbles out like the gas in the soda
water, except, that the bubbles are smaller and cuter, that is what
giving the soft look to the glaze. Because of this reason whenever I
have to add alumina to a glaze, I add the last.
Ababi Sharon
Kibbutz Shoval- Israel
Glaze addict
ababisha@shoval.org.il
http://members4.clubphoto.com/ababi306910/
http://www.milkywayceramics.com/cgallery/asharon.htm
http://www.israelceramics.org/
---------- Original Message ----------
>>1. Alumina will help keep the bubbles smaller because it reduces
>viscosity.
>>
>I am trying to understand this. I am sure you meant that Alumina
>increases
>the viscosity. So I am assuming that because of the increase in
>viscosity
>it is more difficult for the bubbles to expand as the pressure exerted
>on
>them would be greater in a glaze of high viscosity than in one of low
>viscosity. does this make sense? Is this in fact what you are saying?
>Margaret
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