ARTMOLIN@ACS.EKU.EDU on tue 18 feb 97
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Subj: reformulating glazes to a lower cone
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From: shelford@mail.island.net (The Shelfords)
Subject: reformulating glazes to a lower cone
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Hi everybody -
Some friends and I are having to take some cone 10 reduction glazes and
reformulate them to something roughly equivalent and workable for cone 6
oxidation. I haven't tried to reformulate from reduction to oxidation
before, and wonder if there are pitfalls to watch out for, or useful tips
that anyone could share. We will be taking the following steps:
1. Testing the original recipes at cone 10 ox.
2. Testing the original recipes at cone 6 ox.
3. Using an early version of the INSIGHT glaze calculation program, I have
lowered the alumina/silica quantities to numbers within the cone 6 firing
range as indicated in the limit formula chart that came with the program,
trying to keep roughly the same ratio between them, and then we will test
those reformulations.
4. Studying all the tests to see what directions they need to be pushed in
(under- or over-fired, too glossy, too matt, crazing or shivering, colour
and surface activity etc.) and then attempt further reformulations and tests.
Questions:
- Any suggestions for what to do if some of the original glazes don't
calculate out to anything remotely resembling the limit formulas for ^10?
Obviously, a lot of good recipes are non-standard, but reformulating them is
tricky. In most of the cases I have on hand, the oddity lies in the silica
amounts being more appropriate for a ^04 maturity than ^10, but the alumina
is right up there at the top of the range. I have lowered the alumina to
the ^6 range, but if I tried to lower the silica to the same ratio, there
wouldn't be any left. At the moment, we are intending to test a lowered
silica, but not much lowered; and also just arbitrarily raising the silica
to the ^6 level. I suspect with the latter we will get a workable glaze
that bears no resemblance to the original, but what the heck, we'll see. If
anyone knows how these low-silica oddities work, I would love to hear from them.
- If there are any technical or non-technical tricks to modifying glazes for
different cones and different types of firing, it would be really
interesting to hear about them. I have not found any but the most
rudimentary comments on this subject in my various reference books.
I am REALLY enjoying clayart - it is keeping my spirits up while I am
"between studios" and unable to work. TIA for any help or comments. If you
want to e-mail me directly, please do so.
Veronica on Thetis Island in the Gulf of Georgia in BC
e-mail: shelford@island.net
PJLewing@aol.com on wed 19 feb 97
I have time to only post a very brief reply here before I head out to the
Seattle Home Show for my 10 hours of booth time today (day 4 of 9).
But on the subject of lowering the maturing temperature of glazes- 4 or 5
cones is a lot! It almost never works to use the standard rule of thumb of
keeping the Al/Si ratio the same, the flux balance the same, and lowering the
Al and Si both to about the same place in their respective limit formulas.
There's just not enough Al or Si in a a ^6 glaze to take it down that far.
So you end up introducing another element such as boron, which changes
everything. Then it's just not the same glaze. Remember, as Ken Stevens
always says, "When you change the glaze, it's a different glaze."
One trick you can use is to recalculate the glaze using a frit such as 3110,
which has almost no Al in it. Then you can take out Al from that and still
leave yourself enough clay in the recipe to keep it suspended.
I hope this helps.
Paul Lewing
ARTMOLIN@ACS.EKU.EDU on wed 19 feb 97
From: IN%"Tom.Buck@freenet.hamilton.on.ca" "Tom Buck" 18-FEB-1997 13:58:05.62
To: IN%"ARTMOLIN@ACS.EKU.EDU"
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Subj: RE: reformulating glazes to a lower cone/forwarded
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From: Tom Buck
Subject: Re: reformulating glazes to a lower cone/forwarded
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doing -bs
Veronica: 1) If the glaze is balanced (ie, the Silica/Alumina ratio is in
the ballpark for the firing range), then adjust the SiO2 and Al2O3 amounts
downward to C6 limits. But as you do so, recognize that the fluxes and
the colourants will have a bigger effect now, so the glze may become
runny, and you will have to change the flux oxide mix accordingly. (Or
increase the Al2O3 a tad.
2) If the glaze is beyond the C10 limits for Ratio, then what you
do is keep the silica where it is and raise the almunia substantially,
making CaO your main flux oxide, again compared to the usual C6 limits. If
the glaze goes to dry, add say 10% B2O3 to make it more satiny.
There are some other minor factors but these are the main ones.
I help if you need it.
Cheers Tom.Buck@freenet.hamilton.on.ca
Hamilton, Ontario, Canada
Lili Krakowski on wed 19 feb 97
A question. Why do you, like so many people, want to recalculate c.10
glazes to a lower temp. when so many excellent recipes for so many
excellent c.6 or whatever glazes exist? Definitely some glaze effects
seem to be unattainable at certain lower temps, while some lower temp
results cannot be achieved at hight temps. Some results cannot be
achieved in oxidation that can be had in reduction. And vice versa. Isn't
this a bit like all those Reduced Fat recipes and products that do not
even come close to the yumminess and scumptiousness of the Full Fat
ones? Why not just GIVE up the cookies and the icecream and enjoy what
Nature made low fat to begin with like fruit and yoghurt?
Lili Krakowski lkkrakow@edisto.cofc.edu
Dinah Collopy on thu 20 feb 97
I didn't recalulate the receipe, but I was told by someone who had taught
ceramics for many years to increase the amount of Gerstley Borate in a glaze
by 8% and that should bring the ^10 glaze down to a ^6. That did work on the
glaze I was working with.
I was a bit confused by adding 8%. I wasn't sure if the G.B. amount was 20%,
would it end up being 28% or 21.6% (8% of 20 is 1.6). It's the latter.
Dinah
ARTMOLIN@ACS.EKU.EDU on sun 23 feb 97
From: IN%"shelford@mail.island.net" 22-FEB-1997 10:35:08.64
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Subj: RE: reformulating glazes to a lower cone
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From: shelford@mail.island.net (The Shelfords)
Subject: Re: reformulating glazes to a lower cone
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Hi Lili -
Re your comments:
>A question. Why do you, like so many people, want to recalculate c.10
>glazes to a lower temp. when so many excellent recipes for so many
>excellent c.6 or whatever glazes exist? Definitely some glaze effects
>seem to be unattainable at certain lower temps, while some lower temp
>results cannot be achieved at hight temps. Some results cannot be
>achieved in oxidation that can be had in reduction. And vice versa
..> Isn't this a bit like all those Reduced Fat recipes and products that do not
>even come close to the yumminess and scumptiousness of the Full Fat
>ones? Why not just GIVE up the cookies and the icecream and enjoy what
>Nature made low fat to begin with like fruit and yoghurt?
I don't know why anyone else wants to do it, but for my part the point of
this exercise is that the Richmond Potters' Club, of which I am an
out-of-town member, is having a workshop with the British potter John Calver
in April. As you probably know, John specializes in beautiful functional
ware with a lot of the decorating effect coming from overlays of interesting
glazes. John normally works in ^10 reduction. the Richmond club works in
^6 oxidation. Although we will probably have to have a selection of known
^6 glazes on hand for him to use as substitutes, many of his best effects
come from the inter-play of his own, very idiosyncratic glazes. We felt it
was worth at least our best efforts, however futile, to try to reproduce
those very individual idiosyncrasies in bringing down the cone of his own
recipes. If we fail, we'll settle for the less interesting ^6 glazes at our
disposal.
And in defence of ^6, they will only be less interesting because the time
and experimentation has not been devoted to achieving Calver's particular
effects at that cone, not because it isn't possible. But we haven't had the
workshop yet, and haven't seen enough of his work outside of magazines, to
do that work ahead of time.
But your comments raise other questions for me. The comparison to reduced
fat recipes seems to carry a slight tinge of a moral question, as though to
try to carry glaze recipes across different cones or firing techniques is
not only probably pointless, but somehow intrinsically wrong. I don't have
any objection to moral questions, by the way, but in this case, isn't it
just a technical question, and indeed, for a new potter, part of the
learning process? In the end, one does tend to depend on the recipes
formulated for the appropriate cone, because they work better, generally
speaking. But the effort to translate something interesting into one's own
firing range, while it doesn't duplicate the recipe in question, greatly
adds to one's understanding of the process, and OCCASIONALLY results in a
very interesting new glaze.
I am a GREAT fan of the computer glaze calculation program, although I
haven't used it to anything like the degree that our various clayart experts
have done. But it got me over my first "fear of glazing", and started me on
making up my own glazes, greatly adding to my confidence as well as my
repertoire!
Veronica
Gavin Stairs on mon 24 feb 97
>I don't know why anyone else wants to do it, but for my part the point of
>this exercise is that the Richmond Potters' Club, of which I am an
>out-of-town member, is having a workshop with the British potter John Calver
>in April. As you probably know, John specializes in beautiful functional
>ware with a lot of the decorating effect coming from overlays of interesting
>glazes. John normally works in ^10 reduction. the Richmond club works in
>^6 oxidation. Although we will probably have to have a selection of known
>^6 glazes on hand for him to use as substitutes, many of his best effects
>come from the inter-play of his own, very idiosyncratic glazes. We felt it
>was worth at least our best efforts, however futile, to try to reproduce
>those very individual idiosyncrasies in bringing down the cone of his own
>recipes. If we fail, we'll settle for the less interesting ^6 glazes at our
>disposal.
Hi Veronica,
From my slight understanding of how glazes work, it seems to me that the
best bet to reduce the maturation temperature of a glaze without altering
it's esthetic characteristics (leaving aside the question of oxidation vs.
reduction) is to use a larger number of fluxes. The glaze program will help
you to do this, but it won't tell you what the new melting temperature will
be. The only way to do this more systematically (that I know of) is to go
to the ACA Ceramic Phase diagrams for the mixtures in question, and try to
understand the position of the high cone glaze relative to adjacent
eutectics, and then to try to find a lower temp arrangement with similar
structure. This is a lot of work, and you need to know how close to
equilibrium the original was, and so forth.
Sorry for the technobabble. I suspect that your best practical bet is to
add fluxes and then do line and area blends a la Ian Currey. I just got his
book, and it is a fine explanation of how to do this. If you start with the
cone 10 that you are trying to reproduce as one corner, and a balanced (same
ratio of flux to SiO2, Al2O3, etc) mix with two extra fluxes on the far
corner, and blend the two newcomers along the axes, you may come close. If
none of the trials come down far enough, or fail in some other way, you can
try blending by altering a set of three or four fluxes, two at a time, in
the same way. Or try substituting one flux for another. Even if you find a
fit, you may find that there are differences that have nothing to do with
melting temperature.
Good luck. Gavin
Lili Krakowski on mon 24 feb 97
Let me start somewhere. There has been a very holier than thouish
attitude among high-firing reduction potters for as long as I can
remember which goes back to 1949. There is not space here to go into the
whys, but part of it was the Nipponiphilia introduced by Leach and Hamada
and the people who wre able to go study in Japan becaue either they ahd
the GI Bill or the Yen was cheap. Be all that as it may: These potters
snooted it over those who had only electric kilns which in those days
rarely went about c.4, and sneered at the eathernware potters who were
"mere peasants. THE thing that mattes is the final piece; not the technique.
What I mind and question is THIS ATTITUDE. We are craftsmen and that
means that we do what we do with the materials at hand and develop WITHIN
OURSELVES the adaptability to workd with those materials. There is out
there a wonderful repertoire of c.4-6 glazes, and especially in double
application, they produce a depth and a beauty that is not identical to
but certainlyas lovely as the higher fired reduction ones.
My analogy about fat was meant to say thsi: If your body allows you to
eat lots of fat etc, without harm to it, enjoy enjoy! If however you are
told by eithr your body or your physician that you should cut out fat, I
know--speaking from personal knowledge--that the fat reduced (i.e.
adapted or converted, or recalculated) recipes never are as good as
CHANGING CUISINE AND USING RECIPES THAT ARE NOT ADAPTED, BUT WERE
ORIGINATED IN PLACES WHERE FAT NEVER IS USED IN COOKING. My
opinion,only. Lili Krakowski lkkrakow@edisto.cofc.edu
On Sun, 23 Feb 1997 ARTMOLIN@ACS.EKU.EDU wrote:
> ----------------------------Original message----------------------------
> From: IN%"shelford@mail.island.net" 22-FEB-1997 10:35:08.64
> To: IN%"ARTMOLIN@ACS.EKU.EDU"
> CC:
> Subj: RE: reformulating glazes to a lower cone
>
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> From: shelford@mail.island.net (The Shelfords)
> Subject: Re: reformulating glazes to a lower cone
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>
> Hi Lili -
>
> Re your comments:
> >A question. Why do you, like so many people, want to recalculate c.10
> >glazes to a lower temp. when so many excellent recipes for so many
> >excellent c.6 or whatever glazes exist? Definitely some glaze effects
> >seem to be unattainable at certain lower temps, while some lower temp
> >results cannot be achieved at hight temps. Some results cannot be
> >achieved in oxidation that can be had in reduction. And vice versa
> .> Isn't this a bit like all those Reduced Fat recipes and products that do no
> >even come close to the yumminess and scumptiousness of the Full Fat
> >ones? Why not just GIVE up the cookies and the icecream and enjoy what
> >Nature made low fat to begin with like fruit and yoghurt?
>
> I don't know why anyone else wants to do it, but for my part the point of
> this exercise is that the Richmond Potters' Club, of which I am an
> out-of-town member, is having a workshop with the British potter John Calver
> in April. As you probably know, John specializes in beautiful functional
> ware with a lot of the decorating effect coming from overlays of interesting
> glazes. John normally works in ^10 reduction. the Richmond club works in
> ^6 oxidation. Although we will probably have to have a selection of known
> ^6 glazes on hand for him to use as substitutes, many of his best effects
> come from the inter-play of his own, very idiosyncratic glazes. We felt it
> was worth at least our best efforts, however futile, to try to reproduce
> those very individual idiosyncrasies in bringing down the cone of his own
> recipes. If we fail, we'll settle for the less interesting ^6 glazes at our
> disposal.
>
> And in defence of ^6, they will only be less interesting because the time
> and experimentation has not been devoted to achieving Calver's particular
> effects at that cone, not because it isn't possible. But we haven't had the
> workshop yet, and haven't seen enough of his work outside of magazines, to
> do that work ahead of time.
>
> But your comments raise other questions for me. The comparison to reduced
> fat recipes seems to carry a slight tinge of a moral question, as though to
> try to carry glaze recipes across different cones or firing techniques is
> not only probably pointless, but somehow intrinsically wrong. I don't have
> any objection to moral questions, by the way, but in this case, isn't it
> just a technical question, and indeed, for a new potter, part of the
> learning process? In the end, one does tend to depend on the recipes
> formulated for the appropriate cone, because they work better, generally
> speaking. But the effort to translate something interesting into one's own
> firing range, while it doesn't duplicate the recipe in question, greatly
> adds to one's understanding of the process, and OCCASIONALLY results in a
> very interesting new glaze.
>
> I am a GREAT fan of the computer glaze calculation program, although I
> haven't used it to anything like the degree that our various clayart experts
> have done. But it got me over my first "fear of glazing", and started me on
> making up my own glazes, greatly adding to my confidence as well as my
> repertoire!
>
> Veronica
>
Bill Aycock on tue 25 feb 97
At 09:38 AM 2/24/97 EST, you wrote:
>----------------------------Original message----------------------------
>Let me start somewhere. There has been a very holier than thouish
>attitude among high-firing reduction potters for as long as I can
>remember which goes back to 1949.
> Lili Krakowski lkkrakow@edisto.cofc.edu
>
Lili-
I thought I understood you the first time, and applauded you then- I just
read your explanation for the "speed readers" who forget the "and
understand" part- and I still think I understand your position, and I still
agree.
I am, and have been, a ^6 or 6+ potter, and have (mostly) made up my own
glazes. I am happy that way, for more reasons than a good Psychologist could
find in many sessions. I am proud of the effects I can get, and would only
want to go to ^10 reduction for added curiosity satisfaction.
Your points are well made, I think.
Bill- sitting on Persimmon hill, wondering why more people dont think before
they "shoot" or "Flame"
Bill Aycock --- Persimmon Hill --- Woodville, Alabama, USA
--- (in the N.E. corner of the State)
also-- W4BSG -- Grid EM64vr
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