iandol on mon 3 feb 03
Dear Earl Baum,=20
I think your question should be extended into a general question about =
the instability of glazes.
First though, apart from having very low values for Silica and Alumina, =
as well as an unbalanced ratio, I would expect this to be a pretty good =
Saturated Iron Glaze, and because you have not used any materials which =
might leave a surplus of free Alkali oxides there appears to be no =
reason for dissolution. This only leaves the high GB content as the =
culprit causing the problem.
Now the general question, one which I have asked before and to which no =
satisfactory answer has yet been given. How are we able tell if a glaze, =
which is mat on cooling, has reached the point in its progress where all =
of the ingredients have dissolved so that everything is incorporated =
into the vitreous melt when the cone flops over?
Discounting the Cone 6 recipes in the book published by Ron and John, =
because they were designed to be stable and have been tested to prove =
this is so, I would be suspicious about any cone six recipe unless it =
had been designed from first principles to mature at that level. I =
suspect that many ^6 recipes which are given out to the public at large =
are derived from higher cone glazes by adjusting the Si:Al ratio and =
adding a borate melter to bring the temperature down a few cones.
If, in general, people are prepared to acquire recipes I suggest they =
ask for the pedigree as well.
Best regards,
Ivor Lewis. Redhill, South Australia.
Lily Krakowski on tue 4 feb 03
iandol writes:
I suspect that many ^6 recipes which are given out to the public at large
are derived from higher cone glazes by adjusting the Si:Al ratio and adding
a borate melter to bring the temperature down a few cones.
Just a minute, folks. There was a wealth of very good, sound c4-6 glazes
around long before Gama-globulin hit the American clay scene. The CM Hand
book of Behrens glazes has original copyright 1971. As this is a
compendium, I am sure the glazes go back much further. The Scheirs fired at
c. 4 or so. At S.A.C. in 1951 that is what we used and fired, as did our
teacher, Hobart Cowles.
For reasons unknown, when fuel costs rose and many potters decided that they
wanted to fire lower, THEY decided to adapt THEIR glazes to lower temps,
rather than use existing c. 6 glazes. "Everyone" was following the boradly
given advice to replace feldspar with NephSy. And I remember a piece by
Thomas Gallucci (I hope I have spelling's right) in which he suggested that
firing at c. 6 was lowering one's aesthetic! Mine not being temperature
related, I wrote back pointing out all the above.
If you go to Berhrens or to Cowles, and I expect many others' glazes--check
old issues of CM-- they will have all the virtues a glaze can have. Those
people knew just as much about glazes as the current digitally oriented
ones.
Yours at c.6,
Lili Krakowski
P.O. Box #1
Constableville, N.Y.
(315) 942-5916/ 397-2389
Be of good courage....
Baum on tue 4 feb 03
All of your points and the questions that flow from them are very well
received. Let me see if I can stretch a bit and answer, based on my own
(very limited!) understanding...
I believe that the glaze reacts as it does mostly due to the lack of
silica (as someone mentioned earlier, B2O3 is also a glass former, but
it's not as durable). The low silica is obvious from the unity formula,
but it gives me a starting point from which to build towards a more
functional glaze. The challenge here is to keep the desirable qualities
of the glaze - the MgO Matte surface, color and fit - while increasing
both silica (and alumina where necessary) enough to make the glaze into
a stable and durable glass. One catch here is that I have to keep the
alumina relatively low to keep both the color and surface that I find so
attractive in this glaze.
My understanding of the MgO matte surface is that it's caused by
crystallization during cooling, rather than immaturity. I will do
additional tests to verify this, including deliberate over and
under-firing and draw rings, just to be on the safe side.
As for ^6 glazes in general, so long as they are well-crafted with
regard to the established limit formulas, properly tested and used
accordingly, then their source and ancestry is not an issue. Obviously,
it doesn't work to take a glaze from *any* source and use it on
food-contact surfaces without some testing in your own environment, with
your clays and firing schedules.
???
Earl
-----Original Message-----
From: iandol [mailto:iandol@tell.net.au]
Sent: Monday, February 03, 2003 1:56 AM
To: baum@CHARTER.NET
Cc: clayart@LSV.CERAMICS.ORG
Subject: : ^6 Iron Red Question. Make that a general question
Dear Earl Baum,
I think your question should be extended into a general question about
the instability of glazes.
First though, apart from having very low values for Silica and Alumina,
as well as an unbalanced ratio, I would expect this to be a pretty good
Saturated Iron Glaze, and because you have not used any materials which
might leave a surplus of free Alkali oxides there appears to be no
reason for dissolution. This only leaves the high GB content as the
culprit causing the problem.
Now the general question, one which I have asked before and to which no
satisfactory answer has yet been given. How are we able tell if a glaze,
which is mat on cooling, has reached the point in its progress where all
of the ingredients have dissolved so that everything is incorporated
into the vitreous melt when the cone flops over?
Discounting the Cone 6 recipes in the book published by Ron and John,
because they were designed to be stable and have been tested to prove
this is so, I would be suspicious about any cone six recipe unless it
had been designed from first principles to mature at that level. I
suspect that many ^6 recipes which are given out to the public at large
are derived from higher cone glazes by adjusting the Si:Al ratio and
adding a borate melter to bring the temperature down a few cones.
If, in general, people are prepared to acquire recipes I suggest they
ask for the pedigree as well.
Best regards,
Ivor Lewis. Redhill, South Australia.
iandol on wed 5 feb 03
MessageDear Earl,
I agree with you all the way.
I would imagine Magnesium silicate will crystallise from a solution as =
Enstatite and Calcium silicate as Wollastonite. Hence a good mat =
surface. And I would imagine that a glaze that incorporated these =
minerals would be stable to dilute organic acids
But the general question still remains to be answered.=20
How are we able tell if a glaze, which is mat on cooling, has reached =
the point in its progress where all of the ingredients have dissolved so =
that everything is incorporated into the vitreous melt when the cone =
flops over?
If I use your model, then I take things on trust.
Thanks for your contribution.
Best regards,
Ivor
----- Original Message -----=20
From: Baum=20
To: 'iandol'=20
Cc: clayart@LSV.CERAMICS.ORG=20
Sent: Wednesday, 5 February 2003 11:35
Subject: RE: : ^6 Iron Red Question. Make that a general question
All of your points and the questions that flow from them are very well =
received. Let me see if I can stretch a bit and answer, based on my own =
(very limited!) understanding...
=20
I believe that the glaze reacts as it does mostly due to the lack of =
silica (as someone mentioned earlier, B2O3 is also a glass former, but =
it's not as durable). The low silica is obvious from the unity formula, =
but it gives me a starting point from which to build towards a more =
functional glaze. The challenge here is to keep the desirable qualities =
of the glaze - the MgO Matte surface, color and fit - while increasing =
both silica (and alumina where necessary) enough to make the glaze into =
a stable and durable glass. One catch here is that I have to keep the =
alumina relatively low to keep both the color and surface that I find so =
attractive in this glaze.
=20
My understanding of the MgO matte surface is that it's caused by =
crystallization during cooling, rather than immaturity. I will do =
additional tests to verify this, including deliberate over and =
under-firing and draw rings, just to be on the safe side.
=20
As for ^6 glazes in general, so long as they are well-crafted with =
regard to the established limit formulas, properly tested and used =
accordingly, then their source and ancestry is not an issue. Obviously, =
it doesn't work to take a glaze from *any* source and use it on =
food-contact surfaces without some testing in your own environment, with =
your clays and firing schedules.
=20
???
=20
Earl
=20
=20
=20
-----Original Message-----
From: iandol [mailto:iandol@tell.net.au]=20
Sent: Monday, February 03, 2003 1:56 AM
To: baum@CHARTER.NET
Cc: clayart@LSV.CERAMICS.ORG
Subject: : ^6 Iron Red Question. Make that a general question
Dear Earl Baum,=20
I think your question should be extended into a general question about =
the instability of glazes.
First though, apart from having very low values for Silica and =
Alumina, as well as an unbalanced ratio, I would expect this to be a =
pretty good Saturated Iron Glaze, and because you have not used any =
materials which might leave a surplus of free Alkali oxides there =
appears to be no reason for dissolution. This only leaves the high GB =
content as the culprit causing the problem.
Now the general question, one which I have asked before and to which =
no satisfactory answer has yet been given. How are we able tell if a =
glaze, which is mat on cooling, has reached the point in its progress =
where all of the ingredients have dissolved so that everything is =
incorporated into the vitreous melt when the cone flops over?
Discounting the Cone 6 recipes in the book published by Ron and John, =
because they were designed to be stable and have been tested to prove =
this is so, I would be suspicious about any cone six recipe unless it =
had been designed from first principles to mature at that level. I =
suspect that many ^6 recipes which are given out to the public at large =
are derived from higher cone glazes by adjusting the Si:Al ratio and =
adding a borate melter to bring the temperature down a few cones.
If, in general, people are prepared to acquire recipes I suggest they =
ask for the pedigree as well.
Best regards,
Ivor Lewis. Redhill, South Australia.
BVCuma on wed 5 feb 03
>>How are we able tell if a glaze, which is mat on cooling,
has reached the point in its progress where all of the ingredients
have dissolved so that everything is incorporated into the
vitreous melt when the cone flops over?<<
________________________
Hi Iandol,
Hadn't given your request for an explanation much thought...
till studying the glaze grid test samples this morning.
I got some mats that were so... totally matt.
That I started wondering too....
for a second, if they even ever were melted at all!
I know they are because of the high unwashed ash and non fritted
calcium magnesium ulexate boron compound content.
This glaze on its own is a clear crackle where it gathers thick
with sparse but dense crystalline patches....
and a mat as mat can be where it runs thin.
It is fully melted no doubt...
I use it in combination with other well melted semi-gloss/gloss glazes
to get variegated surface texture built out of physically structured crystal
formation...
layered atop each other rather than just spreading horizontally..
...very cool ..er, make that... slooow cool!
Anyway...
Would not a simple draw trial of a sample at peak temperature
reveal the true status of the melt at the time of "cone flop"?
I mean I'm sure the sugar crystal mat I am getting is a high gloss,
transparent, fully melted and stable (?) glaze...
Actually, I doubt the stability....
Who knows... I mean,
I run all my tests on both top and bottom shelf..
because they don't resemble each other here nor there...
try to cut down on the variables and still get..no consistency.
So I am developing glazes for the top
independent from the ones for the bottom....
As if things were not complicated enough already.
Besides....
I have given up trying to search for the path I have come...
Having paced back and forth and walked in circles silly
trying to find my foot prints again...for a repeat.
Like waves from the sea..they are simply washed away...
vanished.
Now I just keep moving on..a step at a time...evolving
letting the past die....
just a few souvenirs to remind me that it ever was at all.
Coming to accept that..and beginning to trust it too...
..Letting go.
BVCuma
Baum on fri 7 feb 03
I think I see the point of your question...
If the melt is complete, with all ingredients dissolved/incorporated in
the glaze, the a draw ring pulled at peak temperature should be a glossy
glass. The draw ring can then be tested with the same criteria as the
mature matte surface. The matte surface only forms during cooling.
So a glossy surface would tend to indicate a complete melt, while a
matte surface at peak temperature would indicate an immature, unmelted
glaze.
Or am I missing something (not at all unlikely)?
Earl
And it's a rainy night in Georgia.....
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of iandol
Sent: Wednesday, February 05, 2003 1:43 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: : ^6 Iron Red Question. Make that a general question
MessageDear Earl,
I agree with you all the way.
I would imagine Magnesium silicate will crystallise from a solution as
Enstatite and Calcium silicate as Wollastonite. Hence a good mat
surface. And I would imagine that a glaze that incorporated these
minerals would be stable to dilute organic acids But the general
question still remains to be answered.
How are we able tell if a glaze, which is mat on cooling, has reached
the point in its progress where all of the ingredients have dissolved so
that everything is incorporated into the vitreous melt when the cone
flops over? If I use your model, then I take things on trust. Thanks for
your contribution. Best regards, Ivor
----- Original Message -----
From: Baum
To: 'iandol'
Cc: clayart@LSV.CERAMICS.ORG
Sent: Wednesday, 5 February 2003 11:35
Subject: RE: : ^6 Iron Red Question. Make that a general question
All of your points and the questions that flow from them are very well
received. Let me see if I can stretch a bit and answer, based on my own
(very limited!) understanding...
I believe that the glaze reacts as it does mostly due to the lack of
silica (as someone mentioned earlier, B2O3 is also a glass former, but
it's not as durable). The low silica is obvious from the unity formula,
but it gives me a starting point from which to build towards a more
functional glaze. The challenge here is to keep the desirable qualities
of the glaze - the MgO Matte surface, color and fit - while increasing
both silica (and alumina where necessary) enough to make the glaze into
a stable and durable glass. One catch here is that I have to keep the
alumina relatively low to keep both the color and surface that I find so
attractive in this glaze.
My understanding of the MgO matte surface is that it's caused by
crystallization during cooling, rather than immaturity. I will do
additional tests to verify this, including deliberate over and
under-firing and draw rings, just to be on the safe side.
As for ^6 glazes in general, so long as they are well-crafted with
regard to the established limit formulas, properly tested and used
accordingly, then their source and ancestry is not an issue. Obviously,
it doesn't work to take a glaze from *any* source and use it on
food-contact surfaces without some testing in your own environment, with
your clays and firing schedules.
???
Earl
-----Original Message-----
From: iandol [mailto:iandol@tell.net.au]
Sent: Monday, February 03, 2003 1:56 AM
To: baum@CHARTER.NET
Cc: clayart@LSV.CERAMICS.ORG
Subject: : ^6 Iron Red Question. Make that a general question
Dear Earl Baum,
I think your question should be extended into a general question about
the instability of glazes.
First though, apart from having very low values for Silica and
Alumina, as well as an unbalanced ratio, I would expect this to be a
pretty good Saturated Iron Glaze, and because you have not used any
materials which might leave a surplus of free Alkali oxides there
appears to be no reason for dissolution. This only leaves the high GB
content as the culprit causing the problem.
Now the general question, one which I have asked before and to which
no satisfactory answer has yet been given. How are we able tell if a
glaze, which is mat on cooling, has reached the point in its progress
where all of the ingredients have dissolved so that everything is
incorporated into the vitreous melt when the cone flops over?
Discounting the Cone 6 recipes in the book published by Ron and John,
because they were designed to be stable and have been tested to prove
this is so, I would be suspicious about any cone six recipe unless it
had been designed from first principles to mature at that level. I
suspect that many ^6 recipes which are given out to the public at large
are derived from higher cone glazes by adjusting the Si:Al ratio and
adding a borate melter to bring the temperature down a few cones.
If, in general, people are prepared to acquire recipes I suggest they
ask for the pedigree as well.
Best regards,
Ivor Lewis. Redhill, South Australia.
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