Ron Roy on sun 14 mar 99
Hi Barn,
First of all - don't try to make glazes without alumina - they will just
run off your ware - just keep it on the low side - It's not hard to get
that blue flush. It's from calcium borate crystals and much easier to get
on iron bearing clay - come to think of it I've never seen it happen on
porcelain.
The reason you need less alumina - alumina prevents (slows down) the
formation of crystals. The blue is a direct result of the the
calcium/borate devitrification.
So if you are getting the blush and don't want it - add more alumina.
RR
>----------------------------Original message----------------------------
>I'm thinking of trying to get a boron blue at cone 6. I've had some
>success with some existing glazes but I'd like to get just the boron
>blue if I can. From my reading this seems to require a low alumina
>high alkaline glaze and probably the high end for B2O3. I've got a few
>recipes to work on and test, but it got me to thinking. Is it possible
>to find a glaze with no alumina that is durable and safe? Are there
>any other material that can be added to the glaze to replace the alumina?
>I've read that crystal glazes have been formulated without alumina, and
>I can imagine they were runny. If I kept the CaO and MgO high would the
>CaO give me enough durablity and the MgO stiffen it enough to make it
>usable? The silica would be high and then I'd probably need to push the
>KNaO to bring the co-eff of expn up. Or is the alumina component that
>critical?
>Barney
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
Barney Adams on mon 15 mar 99
Thanks Ron,
I take it from your answer that there is'nt another oxide that can fill in
or substitute for alumina. I was thinking that bringing MgO to it's upper
limit might make up for alumina being sightly low since it stiffens the glaze.
Or is what's going on too diffrent to apply this way? Is alumina only
providing for a stiffening of the glaze and adjusting the melt point?
in a similar way I would imagine that one should be able to adjust for
being low in silica by adding B2O3 since both work as glass-formers,
but I suspect that boron's dual role in the process is in a smaller window
(in regards to temp range) than alumina which is'nt really regard as flux
until very high temps.
I may have to re-read some of the materials.
Thanks
Barney
Ron Roy wrote:
> ----------------------------Original message----------------------------
> Hi Barn,
>
> First of all - don't try to make glazes without alumina - they will just
> run off your ware - just keep it on the low side - It's not hard to get
> that blue flush. It's from calcium borate crystals and much easier to get
> on iron bearing clay - come to think of it I've never seen it happen on
> porcelain.
>
> The reason you need less alumina - alumina prevents (slows down) the
> formation of crystals. The blue is a direct result of the the
> calcium/borate devitrification.
>
> So if you are getting the blush and don't want it - add more alumina.
>
> RR
>
> >----------------------------Original message----------------------------
> >I'm thinking of trying to get a boron blue at cone 6. I've had some
> >success with some existing glazes but I'd like to get just the boron
> >blue if I can. From my reading this seems to require a low alumina
> >high alkaline glaze and probably the high end for B2O3. I've got a few
> >recipes to work on and test, but it got me to thinking. Is it possible
> >to find a glaze with no alumina that is durable and safe? Are there
> >any other material that can be added to the glaze to replace the alumina?
> >I've read that crystal glazes have been formulated without alumina, and
> >I can imagine they were runny. If I kept the CaO and MgO high would the
> >CaO give me enough durablity and the MgO stiffen it enough to make it
> >usable? The silica would be high and then I'd probably need to push the
> >KNaO to bring the co-eff of expn up. Or is the alumina component that
> >critical?
> >Barney
>
> Ron Roy
> 93 Pegasus Trail
> Scarborough, Ontario
> Canada M1G 3N8
> Tel: 416-439-2621
> Fax: 416-438-7849
>
> Web page: http://digitalfire.com/education/people/ronroy.htm
mgsmith on tue 16 mar 99
A better move than re-reading might be to test the strength of the glaze bond
(with itself and with the body.). You should find that alumina is ten to one
hundred times stronger that B2O3. The effect of changeing the viscosity of the
melt is like putting on an heavy overcoat- be sure that you want the protection
from the envirment. You might want your oxides to "feel" the wind on their skin.
Miles G. Smith
http://home1.gte.net/mgsmith/index.htm
Barney Adams wrote:
> ----------------------------Original message----------------------------
> Thanks Ron,
> I take it from your answer that there is'nt another oxide that can fill in
> or substitute for alumina. I was thinking that bringing MgO to it's upper
> limit might make up for alumina being sightly low since it stiffens the glaze.
>
> Or is what's going on too diffrent to apply this way? Is alumina only
> providing for a stiffening of the glaze and adjusting the melt point?
> in a similar way I would imagine that one should be able to adjust for
> being low in silica by adding B2O3 since both work as glass-formers,
> but I suspect that boron's dual role in the process is in a smaller window
> (in regards to temp range) than alumina which is'nt really regard as flux
> until very high temps.
>
> I may have to re-read some of the materials.
>
> Thanks
> Barney
>
> Ron Roy wrote:
>
> > ----------------------------Original message----------------------------
> > Hi Barn,
> >
> > First of all - don't try to make glazes without alumina - they will just
> > run off your ware - just keep it on the low side - It's not hard to get
> > that blue flush. It's from calcium borate crystals and much easier to get
> > on iron bearing clay - come to think of it I've never seen it happen on
> > porcelain.
> >
> > The reason you need less alumina - alumina prevents (slows down) the
> > formation of crystals. The blue is a direct result of the the
> > calcium/borate devitrification.
> >
> > So if you are getting the blush and don't want it - add more alumina.
> >
> > RR
> >
> > >----------------------------Original message----------------------------
> > >I'm thinking of trying to get a boron blue at cone 6. I've had some
> > >success with some existing glazes but I'd like to get just the boron
> > >blue if I can. From my reading this seems to require a low alumina
> > >high alkaline glaze and probably the high end for B2O3. I've got a few
> > >recipes to work on and test, but it got me to thinking. Is it possible
> > >to find a glaze with no alumina that is durable and safe? Are there
> > >any other material that can be added to the glaze to replace the alumina?
> > >I've read that crystal glazes have been formulated without alumina, and
> > >I can imagine they were runny. If I kept the CaO and MgO high would the
> > >CaO give me enough durablity and the MgO stiffen it enough to make it
> > >usable? The silica would be high and then I'd probably need to push the
> > >KNaO to bring the co-eff of expn up. Or is the alumina component that
> > >critical?
> > >Barney
> >
> > Ron Roy
> > 93 Pegasus Trail
> > Scarborough, Ontario
> > Canada M1G 3N8
> > Tel: 416-439-2621
> > Fax: 416-438-7849
> >
> > Web page: http://digitalfire.com/education/people/ronroy.htm
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