Christy Pines on thu 9 sep 04
flint and silica.
In every "recipe" I have in my spreadsheet that calls for Wollastonite,
the recipe also calls for Silica or Flint. So now you have me curious
about this. When I did Brian Gartside's workshop, one of the raw
materials that I liked a lot, in terms of the effects I got, was
Wollastonite. Plus I just like the name. But still, could I get rid of
Silica/Flint in the recipe if I could determine that the Wollastonite
was going to provide that piece of the puzzle?
christy in connecticut
cpines at ix.netcom.com
Lee Love wrote:
> John Reeve uses Wollastonite as a finer silica
> source in his synthetic glazes, like his synthetic Mashiko Kaki.
>
Lee Love on fri 10 sep 04
flint and silica.
Hi Christy,
He said that it added it for fine silica (I use nuka bai and
straw ash for this.). Of course, how much CaSiO3 you can use depends
on how much calcium your glaze needs.
Wollastonite forms from the interaction of limestones, that contain
calcite, CaCO3, with the silica, SiO2, in hot magmas. This happens when
hot magmas intrude into and/or around limestones or from limestones
chunks that are broken off into the magma tubes under volcanoes and then
blown out of them. It forms by the following formula:
CaCO3 + SiO2 ----> CaSiO3 + CO2
--
Lee in Mashiko, Japan http://mashiko.org
http://www.livejournal.com/users/togeika/ WEB LOG
http://public.fotki.com/togeika/ Photos!
Lee Love on fri 10 sep 04
flint and silica.
Ron Roy wrote:
>Yes again - amorphous silica is more easily integrated into the melt.
>Particle size as well - has an effect on how fast melting proceedes. Try
>making a glaze with silica sand and see how far you get for instance.
>
In the other direction: to get the finest silica, organic ash
is the best source. Here in Japan, rice straw ash and rice hull ash
is the main source. John Reeve uses Wollastonite as a finer silica
source in his synthetic glazes, like his synthetic Mashiko Kaki.
--
Lee in Mashiko, Japan http://mashiko.org
http://www.livejournal.com/users/togeika/ WEB LOG
http://public.fotki.com/togeika/ Photos!
Ivor and Olive Lewis on sat 11 sep 04
flint and silica.
Dear Christy Pines,
Wollastonite is a wonderful material, providing a way of getting Lime
into a glaze at lower maturity temperatures.
But Wollastonite will never provide all the Silica needed to make a
good stable vitrified glaze (Transparent and Glossy) at cone six, or
at any other temperature. So you have to include a source of free
Silicon dioxide to make up the difference.
I suppose this advice can be ignored if you intend experimenting
outside generally accepted limit values for the oxide groups.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Ron Roy on sat 11 sep 04
flint and silica.
Hi Christy,
This is where glaze calculation shines - subbing in materials and getting
the same glaze. In most glazes - if you try to provide all the silica you
need by using wolastonite you would not be able to have much of any other
flux because there would be so much CaO.
A typical stable glaze at cone 6 would have between 60 and 70% SiO2 and CaO
would perhaps be in the 15 to 16% range.
Wolastonite gives about 43% CaO and 53% SiO2.
So you can see why it would be practically impossible to get enough SiO2
from Wolastonite.
There are some exceptions - for instance high alumina mattes - which
require lower amounts of SiO2 - it is possible to then get all the silica
you need from Feldspars, Clays, Talc and frits. In fact I have worked on
some of those types of glazes where I had to take out some or all of the
Wolastonite - to get rid of some silica - to keep the SiO2/Al2O3 ratio down
low enough to get devitrification (matte surface) during cooling.
RR
>In every "recipe" I have in my spreadsheet that calls for Wollastonite,
>the recipe also calls for Silica or Flint. So now you have me curious
>about this. When I did Brian Gartside's workshop, one of the raw
>materials that I liked a lot, in terms of the effects I got, was
>Wollastonite. Plus I just like the name. But still, could I get rid of
>Silica/Flint in the recipe if I could determine that the Wollastonite
>was going to provide that piece of the puzzle?
>
>christy in connecticut
>cpines at ix.netcom.com
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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