Jorge Nabel on tue 8 apr 08
I have been talking to another ceramist who told me to use silica fume
in glazes.
He says that it might control green shrinkage and help with crazing.
Has anyone used this coloidal silica on glazes ? How do you work with it as
it is very hard to mix with water. Does this sound like a reasonable advise?
We were talking teoretically but I thought it could be a good question
for Clayart.
Thanks
Jorge en Buenos Aires
Steve Slatin on tue 8 apr 08
Jorge -- I only know of silica fume being used in
concrete work -- I've never seen a reference to it
being used in ceramics. I can't think of any reason
why it would react differently from the kind of
silica or flint normally used in sourcing silica
into a glaze.
All silica will lower COE/CTE in a glaze, unless
the glaze is already overloaded with silica (then
it can actually have the opposite effect). Since
the colloidal silicas generally convert to crystalline
forms under heat well below glazing temperatures,
I'd suspect there's no difference in final effect.
Just my opinion -- Steve Slatin
Jorge Nabel wrote:
I have been talking to another ceramist who told me to use silica fume
in glazes.
He says that it might control green shrinkage and help with crazing.
Has anyone used this coloidal silica on glazes ? How do you work with it as
it is very hard to mix with water. Does this sound like a reasonable advise?
We were talking teoretically but I thought it could be a good question
for Clayart.
Thanks
Jorge en Buenos Aires
---------------------------------
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Jim Murphy on wed 9 apr 08
Hi Jorge,
"Silica Fume" is a by-product of steel or other industrial production.
Accordingly, there may be many 'impurities' in silica fume. Relatively cheap
if you can get it and may still be used in glaze ... in small amounts.
OTOH, "Fumed Silica" is a 'pure' precipitated form of silicon dioxide that
is produced chemically.
"Fumed Silica" is one form of synthetic amorphous [non-crystalline] silica.
Typically, only ~1-2% amorphous silica is added to a glaze to help control
expansion/contraction. The extremely small [submicron] particle size may
present viscosity-related mixing problems, though it's quite possible to
handmix small glaze batches using a metal spatula [IF we're talkin' only
1-2% addition].
Best wishes,
Jim Murphy
Fredrick Paget on thu 10 apr 08
Jorge,
We used fume silica in adhesives and coatings as a thickener before I
retired. In non - aquaous mixtures a very small percentage will
thicken up a liquid mixture and make it thixotropic. But then you
probably know this.
In water mixes it acts weird and at first it thickens but as time
goes by - a few minutes it thins out. .About 3 percent by weight in a
liquid epoxy will make a stiff paste. In water it does at first but
goes all lumpy and weird.
Also the stuff is expensive. It is sold in 10 pound bags that are I
would guess about 3 or 4 cubic feet. It is so light and fluffy it
floats in the air.
The trade name is Cabosil.
I suppose you could mix up a glaze with oil, alcohol, or paint
thinner instead of water and use Cabosil but it would be hard to get
enough in there as you would have a dry lump with enough in the mix
to do any good. Use regular silica for the bulk of the requirement
and just enough Cabosil to thicken it up like cream and such a glaze
might work.
Fred Paget
Twin Dragon Studio
Mill Valley, CA, USA
fredrick@well.com
Charter Member Potters Council
>Steve, silica fumes are an important portion of the rigidizer.
>On thermal ceramics you can read "Kaowool Rigidizer is a colloidal
>silica compound for treating. surfaces of Kaowool ceramic "
>So I thought a similar effect could have on glazes on green.But it
>might be a small
>fraction,some drops,perhaps?
>On the other hand, its particle size is very small. Its obtained from
>the fumes of silica
>on an electric kiln. Hence, its surface is huge and can be combined
>more easily and
>at lower temperatures.
>But this is theoretical for me.Wanted to know if anybody has some experience.
>Anyone?
>Regards
>jorge en Buenos Aires
>
>www.jorgenabel.com
>
>
>
>
>
>
--
Jorge Nabel on thu 10 apr 08
Steve, silica fumes are an important portion of the rigidizer.
On thermal ceramics you can read "Kaowool Rigidizer is a colloidal
silica compound for treating. surfaces of Kaowool ceramic "
So I thought a similar effect could have on glazes on green.But it
might be a small
fraction,some drops,perhaps?
On the other hand, its particle size is very small. Its obtained from
the fumes of silica
on an electric kiln. Hence, its surface is huge and can be combined
more easily and
at lower temperatures.
But this is theoretical for me.Wanted to know if anybody has some experience.
Anyone?
Regards
jorge en Buenos Aires
www.jorgenabel.com
Steve Slatin wrote
Jorge -- I only know of silica fume being used in
concrete work -- I've never seen a reference to it
being used in ceramics. I can't think of any reason
why it would react differently from the kind of
silica or flint normally used in sourcing silica
into a glaze.
All silica will lower COE/CTE in a glaze, unless
the glaze is already overloaded with silica (then
it can actually have the opposite effect). Since
the colloidal silicas generally convert to crystalline
forms under heat well below glazing temperatures,
I'd suspect there's no difference in final effect.
Just my opinion -- Steve Slatin
Jorge Nabel wrote:
I have been talking to another ceramist who told me to use silica fume
in glazes.
He says that it might control green shrinkage and help with crazing.
Has anyone used this coloidal silica on glazes ? How do you work with it as
it is very hard to mix with water. Does this sound like a reasonable advise?
We were talking teoretically but I thought it could be a good question
for Clayart.
Thanks
Jorge en Buenos Aires
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