Jacqueline Miller on fri 17 feb 06
Barium substitution redox: The glaze recipe. This is the recipe for *Ball
Celadon* from Mark Burlenson's book: Potash feldspar (custer) 24.3, whitin=
g
19.2, Kaolin (grolleg) 19.6, flint 36.9, barium carbonate 2.0, tin oxide 1.=
0.
It has a low barium content so am wondering if I can just substitute
strontium 1.5. Also is grolleg kaolin the same as EPK? This is a thick
soft, satin transparent glaze with tints of blue and pink. Thank you all
for your responses to my previous email and I look forward to your thoughts
about the substitution in this glaze. Jackie
Miller
John Britt on sat 18 feb 06
Jackie,
I believe that I am the one who submitted that recipe to Mark=92s book. And
I have to completely disagree with Ron here.
There will be a tremendous difference if you substitute grolleg with EPK!
One will be blue-green to green celadon and the other a wonderful blue
celadon. Also, substituting strontium carbonate for barium carbonate will
make a difference. As will leaving out the tin oxide or substituting a
zirconium silicate, or using different forms of iron!
I have run thousands and thousands of tests on this glaze by substituting
ingredients. This was the basis of all my studies on glazes. It is a great
place to start learning, as there are only a few main ingredients:
feldspar, silica, whiting, clay. These are the four basic ingredients in
all cone 10 glazes. So running line blends on each of the ingredients or
several together will show you so many things about cone 10 glazes.
To my limited understanding, the defining feature of iron blue celadons is
keeping the titanium oxide low and firing in heavy reduction. This is done
with kaolin=92s that are low in titanium oxide like grolleg. There is no
need to argue who is right, you should just run the test. Do as Ron
suggests and substitute grolleg with EPK. Or for that matter substitute
the grolleg with Tile 6, Kaopaque, Standard, Super Standard, Peerless,
Diamond, Sapphire, Helmar, McNamee, and other kaolin=92s or ball clay=92s li=
ke
OM-4, Tennessee #4 =96 9, XX saggar, etc. Then report back if there is any
difference.
Incidentally, to get an iron blue celadon you will also need to use the
glaze on a grolleg clay body. This makes the body low in titanium oxide
too. So when you run the test, substituting for the kaolin in the glaze
recipe, also fire it on various porcelain and stoneware clay bodies. You
will see a tremendous difference in the color. But be sure to fire it in
heavy reduction!
(I have done all this for you in my book, =93The Complete Guide to High-Fire=
Glazes=94 on page 66- 67. And I have described the firing cycle too.)
Then, since it is an iron glaze you can run line blends on the iron. 1 =96
25%. (This shows you the range of colors you can get from iron: blue, blue
green, green, amber, temmoku, iron saturate, etc.) Then you can run line
blends on the forms of iron: black iron, red iron, yellow iron, brown
iron, yellow ochre, crocus martis, Spanish red iron, synthetic red iron,
synthetic yellow iron, burnt sienna, umber, etc. Then the clays containing
iron, like Barnard (a.k.a. Blackbird slip, if you have it), Ranger red,
Redart and other red clays.
And finally you can run all these through different firing cycles:
reduction, oxidation and striking. (In my book I list some like R1, R2,
R3, O1, O1 and S1 although there are thousands of others to consider.)
using various fuels: electric, gas, oil, coal, sawdust, wood, and the in
different atmospheres like salt or soda.
By this time you will be exhausted and very old, but you will have a
pretty good understanding of an iron blue celadon. And you will also have
learned something about the difference materials make!
This post illustrates the fundamental difference I have with those who
want us to believe that by using the UMF, through various computer
programs, they can substitute oxides and get the same effects. It is
simply not true! We have discussed this many times on Clayart (see
archives).
Now don=92t miss the point, I understand the value of UMF and see that it
has a very valuable place in ceramics. It can help us to understand glazes
and adjust them with great ease. It can help us to target our testing when
materials go out of production or are no longer available. But it does not
account for many, many other things that are critical to the outcome of
the glaze. There is not substitute for empirical testing, as I am sure Ron
will agree.
You can substitute molecules all you want, but the results will not be the
same, and they still must be empirically tested. Barium Oxide has
different properties than Strontium Oxide. (Incidentally, this glaze is
very stable (lots of alumina and silica) and I have tested it at least
three times for barium leaching and it was always very low. Of course you
should test your own glazes.) EPK has different physical and chemical
properties than grolleg kaolin, etc.
The computer programs are only as good as the information fed in, like the
percent analysis, which is an average, does not include all trace amounts
and is sometimes reported incorrectly, both accidentally and on purpose.
Also, the computer programs do not account for the physical properties of
the source oxide and for that you must rely on the operator. Nor do they
account for the firing.
For example: a computer program does not tell you that a shino will be
carbon trap because it has sodium oxide. This is because the sodium oxide
can come from soluble or insoluble sources and that will make all the
difference. And the firing is what makes the carbon. So only the operator
can know this from experience not from the UMF, and certainly not from the
computer program.
And in this case, the computer will not know that grolleg kaolin will make
a difference, and so you will miss out on a fantastic glaze.
So, I guess the moral of the story is: Don=92t believe everything you read,
test your own shit and come to your own conclusions, and Clayart Rules!
Hope it helps,
John Britt
www.johnbrittpottery.com
Ron Roy on sat 18 feb 06
Hi Jackie,
Yes - if you use Grolleg - 1.5 Strontium or 1.0 more whiting.
If you use EPK - it is probably a little bit more refractory so then use
2.0 Strontium or 1.5 more whiting.
I'm sure there will be no diference that you can see in that glaze.
RR
>Barium substitution redox: The glaze recipe. This is the recipe for *Ball
>Celadon* from Mark Burlenson's book: Potash feldspar (custer) 24.3, whiting
>19.2, Kaolin (grolleg) 19.6, flint 36.9, barium carbonate 2.0, tin oxide 1.0.
>It has a low barium content so am wondering if I can just substitute
>strontium 1.5. Also is grolleg kaolin the same as EPK? This is a thick
>soft, satin transparent glaze with tints of blue and pink. Thank you all
>for your responses to my previous email and I look forward to your thoughts
>about the substitution in this glaze. Jackie
>Miller
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Jacqueline Miller on sun 19 feb 06
Ron and John: Thank you *so much* for your help. You are incredible sources
of information and inspiration. Hope to meet you at an NCECA when one gets
closer to Ohio. I am experimenting with glaze testing for the first time an=
d
it is addictive. I will do some testing and get back. Jackie
On 2/18/06, John Britt wrote:
>
> Jackie,
>
> I believe that I am the one who submitted that recipe to Mark's book. And
> I have to completely disagree with Ron here.
>
> There will be a tremendous difference if you substitute grolleg with EPK!
> One will be blue-green to green celadon and the other a wonderful blue
> celadon. Also, substituting strontium carbonate for barium carbonate will
> make a difference. As will leaving out the tin oxide or substituting a
> zirconium silicate, or using different forms of iron!
>
> I have run thousands and thousands of tests on this glaze by substituting
> ingredients. This was the basis of all my studies on glazes. It is a grea=
t
> place to start learning, as there are only a few main ingredients:
> feldspar, silica, whiting, clay. These are the four basic ingredients in
> all cone 10 glazes. So running line blends on each of the ingredients or
> several together will show you so many things about cone 10 glazes.
>
> To my limited understanding, the defining feature of iron blue celadons i=
s
> keeping the titanium oxide low and firing in heavy reduction. This is don=
e
> with kaolin's that are low in titanium oxide like grolleg. There is no
> need to argue who is right, you should just run the test. Do as Ron
> suggests and substitute grolleg with EPK. Or for that matter substitute
> the grolleg with Tile 6, Kaopaque, Standard, Super Standard, Peerless,
> Diamond, Sapphire, Helmar, McNamee, and other kaolin's or ball clay's lik=
e
> OM-4, Tennessee #4 =96 9, XX saggar, etc. Then report back if there is an=
y
> difference.
>
> Incidentally, to get an iron blue celadon you will also need to use the
> glaze on a grolleg clay body. This makes the body low in titanium oxide
> too. So when you run the test, substituting for the kaolin in the glaze
> recipe, also fire it on various porcelain and stoneware clay bodies. You
> will see a tremendous difference in the color. But be sure to fire it in
> heavy reduction!
>
> (I have done all this for you in my book, "The Complete Guide to High-Fir=
e
> Glazes" on page 66- 67. And I have described the firing cycle too.)
>
> Then, since it is an iron glaze you can run line blends on the iron. 1 =
=96
> 25%. (This shows you the range of colors you can get from iron: blue, blu=
e
> green, green, amber, temmoku, iron saturate, etc.) Then you can run line
> blends on the forms of iron: black iron, red iron, yellow iron, brown
> iron, yellow ochre, crocus martis, Spanish red iron, synthetic red iron,
> synthetic yellow iron, burnt sienna, umber, etc. Then the clays containin=
g
> iron, like Barnard (a.k.a. Blackbird slip, if you have it), Ranger red,
> Redart and other red clays.
>
> And finally you can run all these through different firing cycles:
> reduction, oxidation and striking. (In my book I list some like R1, R2,
> R3, O1, O1 and S1 although there are thousands of others to consider.)
> using various fuels: electric, gas, oil, coal, sawdust, wood, and the in
> different atmospheres like salt or soda.
>
> By this time you will be exhausted and very old, but you will have a
> pretty good understanding of an iron blue celadon. And you will also have
> learned something about the difference materials make!
>
> This post illustrates the fundamental difference I have with those who
> want us to believe that by using the UMF, through various computer
> programs, they can substitute oxides and get the same effects. It is
> simply not true! We have discussed this many times on Clayart (see
> archives).
>
> Now don't miss the point, I understand the value of UMF and see that it
> has a very valuable place in ceramics. It can help us to understand glaze=
s
> and adjust them with great ease. It can help us to target our testing whe=
n
> materials go out of production or are no longer available. But it does no=
t
> account for many, many other things that are critical to the outcome of
> the glaze. There is not substitute for empirical testing, as I am sure Ro=
n
> will agree.
>
> You can substitute molecules all you want, but the results will not be th=
e
> same, and they still must be empirically tested. Barium Oxide has
> different properties than Strontium Oxide. (Incidentally, this glaze is
> very stable (lots of alumina and silica) and I have tested it at least
> three times for barium leaching and it was always very low. Of course you
> should test your own glazes.) EPK has different physical and chemical
> properties than grolleg kaolin, etc.
>
> The computer programs are only as good as the information fed in, like th=
e
> percent analysis, which is an average, does not include all trace amounts
> and is sometimes reported incorrectly, both accidentally and on purpose.
> Also, the computer programs do not account for the physical properties of
> the source oxide and for that you must rely on the operator. Nor do they
> account for the firing.
>
> For example: a computer program does not tell you that a shino will be
> carbon trap because it has sodium oxide. This is because the sodium oxide
> can come from soluble or insoluble sources and that will make all the
> difference. And the firing is what makes the carbon. So only the operator
> can know this from experience not from the UMF, and certainly not from th=
e
> computer program.
>
> And in this case, the computer will not know that grolleg kaolin will mak=
e
> a difference, and so you will miss out on a fantastic glaze.
>
> So, I guess the moral of the story is: Don't believe everything you read,
> test your own shit and come to your own conclusions, and Clayart Rules!
>
>
> Hope it helps,
>
> John Britt
> www.johnbrittpottery.com
>
>
> _________________________________________________________________________=
_____
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
Jacqueline Miller on sun 19 feb 06
One more question. I am using this glaze on Southern Ice porcelain. I know
nothing about grolleg. Do you know if this is a grolleg based body?
On 2/19/06, Jacqueline Miller wrote:
>
> Ron and John: Thank you *so much* for your help. You are incredible
> sources of information and inspiration. Hope to meet you at an NCECA when
> one gets closer to Ohio. I am experimenting with glaze testing for the fi=
rst
> time and it is addictive. I will do some testing and get back. Jackie
>
> On 2/18/06, John Britt wrote:
> >
> > Jackie,
> >
> > I believe that I am the one who submitted that recipe to Mark's book.
> > And
> > I have to completely disagree with Ron here.
> >
> > There will be a tremendous difference if you substitute grolleg with
> > EPK!
> > One will be blue-green to green celadon and the other a wonderful blue
> > celadon. Also, substituting strontium carbonate for barium carbonate
> > will
> > make a difference. As will leaving out the tin oxide or substituting a
> > zirconium silicate, or using different forms of iron!
> >
> > I have run thousands and thousands of tests on this glaze by
> > substituting
> > ingredients. This was the basis of all my studies on glazes. It is a
> > great
> > place to start learning, as there are only a few main ingredients:
> > feldspar, silica, whiting, clay. These are the four basic ingredients i=
n
> > all cone 10 glazes. So running line blends on each of the ingredients o=
r
> >
> > several together will show you so many things about cone 10 glazes.
> >
> > To my limited understanding, the defining feature of iron blue celadons
> > is
> > keeping the titanium oxide low and firing in heavy reduction. This is
> > done
> > with kaolin's that are low in titanium oxide like grolleg. There is no
> > need to argue who is right, you should just run the test. Do as Ron
> > suggests and substitute grolleg with EPK. Or for that matter substitute
> > the grolleg with Tile 6, Kaopaque, Standard, Super Standard, Peerless,
> > Diamond, Sapphire, Helmar, McNamee, and other kaolin's or ball clay's
> > like
> > OM-4, Tennessee #4 =96 9, XX saggar, etc. Then report back if there is =
any
> >
> > difference.
> >
> > Incidentally, to get an iron blue celadon you will also need to use the
> > glaze on a grolleg clay body. This makes the body low in titanium oxide
> > too. So when you run the test, substituting for the kaolin in the glaze
> > recipe, also fire it on various porcelain and stoneware clay bodies. Yo=
u
> > will see a tremendous difference in the color. But be sure to fire it i=
n
> > heavy reduction!
> >
> > (I have done all this for you in my book, "The Complete Guide to
> > High-Fire
> > Glazes" on page 66- 67. And I have described the firing cycle too.)
> >
> > Then, since it is an iron glaze you can run line blends on the iron. 1 =
=96
> > 25%. (This shows you the range of colors you can get from iron: blue,
> > blue
> > green, green, amber, temmoku, iron saturate, etc.) Then you can run lin=
e
> > blends on the forms of iron: black iron, red iron, yellow iron, brown
> > iron, yellow ochre, crocus martis, Spanish red iron, synthetic red iron=
,
> >
> > synthetic yellow iron, burnt sienna, umber, etc. Then the clays
> > containing
> > iron, like Barnard (a.k.a. Blackbird slip, if you have it), Ranger red,
> > Redart and other red clays.
> >
> > And finally you can run all these through different firing cycles:
> > reduction, oxidation and striking. (In my book I list some like R1, R2,
> > R3, O1, O1 and S1 although there are thousands of others to consider.)
> > using various fuels: electric, gas, oil, coal, sawdust, wood, and the i=
n
> >
> > different atmospheres like salt or soda.
> >
> > By this time you will be exhausted and very old, but you will have a
> > pretty good understanding of an iron blue celadon. And you will also
> > have
> > learned something about the difference materials make!
> >
> > This post illustrates the fundamental difference I have with those who
> > want us to believe that by using the UMF, through various computer
> > programs, they can substitute oxides and get the same effects. It is
> > simply not true! We have discussed this many times on Clayart (see
> > archives).
> >
> > Now don't miss the point, I understand the value of UMF and see that it
> > has a very valuable place in ceramics. It can help us to understand
> > glazes
> > and adjust them with great ease. It can help us to target our testing
> > when
> > materials go out of production or are no longer available. But it does
> > not
> > account for many, many other things that are critical to the outcome of
> > the glaze. There is not substitute for empirical testing, as I am sure
> > Ron
> > will agree.
> >
> > You can substitute molecules all you want, but the results will not be
> > the
> > same, and they still must be empirically tested. Barium Oxide has
> > different properties than Strontium Oxide. (Incidentally, this glaze is
> > very stable (lots of alumina and silica) and I have tested it at least
> > three times for barium leaching and it was always very low. Of course
> > you
> > should test your own glazes.) EPK has different physical and chemical
> > properties than grolleg kaolin, etc.
> >
> > The computer programs are only as good as the information fed in, like
> > the
> > percent analysis, which is an average, does not include all trace
> > amounts
> > and is sometimes reported incorrectly, both accidentally and on purpose=
.
> > Also, the computer programs do not account for the physical properties
> > of
> > the source oxide and for that you must rely on the operator. Nor do the=
y
> >
> > account for the firing.
> >
> > For example: a computer program does not tell you that a shino will be
> > carbon trap because it has sodium oxide. This is because the sodium
> > oxide
> > can come from soluble or insoluble sources and that will make all the
> > difference. And the firing is what makes the carbon. So only the
> > operator
> > can know this from experience not from the UMF, and certainly not from
> > the
> > computer program.
> >
> > And in this case, the computer will not know that grolleg kaolin will
> > make
> > a difference, and so you will miss out on a fantastic glaze.
> >
> > So, I guess the moral of the story is: Don't believe everything you
> > read,
> > test your own shit and come to your own conclusions, and Clayart Rules!
> >
> >
> > Hope it helps,
> >
> > John Britt
> > www.johnbrittpottery.com
> >
> >
> > _______________________________________________________________________=
_______
> > Send postings to clayart@lsv.ceramics.org
> >
> > You may look at the archives for the list or change your subscription
> > settings from http://www.ceramics.org/clayart/
> >
> > Moderator of the list is Mel Jacobson who may be reached at
> > melpots@pclink.com.
> >
>
>
nsmheralds@netzero.net on sun 19 feb 06
Southern Ice is made from halloysite. You may have read the recent disc=
ussion of it here on ClayArt. If not, here's a bit of what information =
I've gleaned so far:
Halloysite is a member of a group of kaolinitic minerals. The chemical =
formula of both halloysite and kaolinite is Al2Si2O5(OH)4. Thus, an oxi=
de analysis will reveal that the two minerals have identical oxide conte=
nt. So what's the difference? I asked myself the same question. Accor=
ding to webmineral.com, kaolinite is a "secondary m=
ineral derived from the wathering of alumino-silicate minerals" and hall=
oysite is "a product of hydrothermal alteration or =
surface weathering of aluminosilicate minerals, as feldspars. Formed by =
dehydration of endellite above 110 deg. C." Endellite is Al2Si2O5(OH)4-=
2(H2O), which essentially means that endellite has two oxygen mollecules=
chemically bound to the rest of it. The mineral data found on webminer=
al.com contains a lot of information, much of which flies right over my =
head in much the same way that deadlines do. The upshot of the above in=
formation is that, if I'm not mistaken, since halloysite is hydrothermal=
ly altered, its internal structure is different than that of ordinary ka=
olinite, which makes it more likely to be transluscent. (This is alalog=
ous to the various types of sugar, which are all C6H12O6, but which diff=
er in the way the atoms are arranged in the mollecule.) If you consult =
your ceramics supply catalog, you should find (if they're being helpful =
enouch) an oxide content analysis of the various kaolins, ball clays, fe=
lspars, etc, that they carry. You'll find that many ball clays are chem=
ically similar to kaolins and that most kaolins, like the well-known EPK=
, contain a good handful of impurities. You will also note that Grolleg=
kaolin is pure kaolinite. The absence of impurities also allows for gr=
eater transluscency, which I think has something to do with the effect t=
hose impurities have on the final crystalline structure of the fired bod=
y. I'm told that straight kaolin is almost impossible to throw, so ther=
e must be more involved. I recently threw a small bowl out of Redding T=
errane laterite, a material derrived by the weathering of basalt, that i=
s mostly kaolinitic clay, alumina and iron oxide. It didn't handle at a=
ll well, although I'm not sure how much of that had to do with the size =
of the particles (it was pretty lumpy) and how much of it had to do with=
the plasticity of the minerals themselves. Further investigation is re=
quired. Anyway, for what it's worth, this bowl is currently in the kiln=
being test-fired to cone 10.
Anyway, you can probably do a google search for halloysite and for Groll=
eg kaolin. You can also talk to you local geologist, who may have some =
corrections to what I've written above.
Nathan Miller
Thistillium Pottery
Newberg, OR
=
Ron Roy on sun 19 feb 06
Hi Jackie,
Yes - John is right about the english kaolins like grolleg - they have less
titanium dioxide and are the right ones for getting a blue celadon.
I should have included that information in my post.
If you use the EPK version the colour will be more green as in a
traditional celadon.
RR
>I believe that I am the one who submitted that recipe to Mark=92s book. And
>I have to completely disagree with Ron here.
>
>There will be a tremendous difference if you substitute grolleg with EPK!
>One will be blue-green to green celadon and the other a wonderful blue
>celadon. Also, substituting strontium carbonate for barium carbonate will
>make a difference. As will leaving out the tin oxide or substituting a
>zirconium silicate, or using different forms of iron!
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
=46ax: 613-475-3513=20
Ron Roy on sun 19 feb 06
I have always said a combination of both is better than the sum of both by
the way - strange how that got overlooked.
The more you use calculation software the more you will realize just how
important it is. I wish I had started using it when I was a young man -
when I think of all the time I wasted mixing thousands of test glazes - and
learning so little from it - I could be miles ahead of where I am now.
I don't think anyone who has not used calculation has the faintest idea of
how great a tool it is - the more skill you have the better it is - isn't
that true of any tool? And isn't it true that the more you work with your
tools the more skilled you become?
RR
John Britt says:
>Now don=92t miss the point, I understand the value of UMF and see that it
>has a very valuable place in ceramics. It can help us to understand glazes
>and adjust them with great ease. It can help us to target our testing when
>materials go out of production or are no longer available. But it does not
>account for many, many other things that are critical to the outcome of
>the glaze. There is not substitute for empirical testing, as I am sure Ron
>will agree.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
=46ax: 613-475-3513=20
Tom Buck on mon 20 feb 06
Ron/John:
=09I admire both Ron Roy & John Britt, and know that proof-testing is
needed. BUT I agree with Ron: glaze calculation is a marvelous tool; and
it allows one to use THREE tests to achieve workable results.... NOT the
100 "pitch & grab" tests of a Cone 10 copper red that a local potter did
(because he could) and at the end, he mounted all the test tiles on a big
board just to demonstrate that he really didn't ever succeed in getting a
satisfactory copper red.
=09Testing can easily be overdone. When you do glzcalc you know your
starting point, and after the first test, you know which way to revise,
and you should come close to a successful glaze on the second test, and
nail it on the third.
=09any potter who wishes to move into a new glaze (for many reasons)
should always start by converting a successful current glaze into a Seger
Formula (UMF in John's terms), and "reverse engineer" the new recipe, test
it, revise, test it again, revise and then get the new glaze to work on
the third try.
=09with the excellent glaze programs currently available at low cost,
no versatile potter should be without one. and it is no great feat to
learn how to use it.
just my experience talking.
later. peace Tom
Tom Buck ) -- primary address.
"alias" or secondary address.
tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street, Hamilton ON L8T 3E1 Canada
On Sun, 19 Feb 2006, Ron Roy wrote:
> I have always said a combination of both is better than the sum of both b=
y
> the way - strange how that got overlooked.
>=20
> The more you use calculation software the more you will realize just how
> important it is. I wish I had started using it when I was a young man -
> when I think of all the time I wasted mixing thousands of test glazes - a=
nd
> learning so little from it - I could be miles ahead of where I am now.
>=20
> I don't think anyone who has not used calculation has the faintest idea o=
f
> how great a tool it is - the more skill you have the better it is - isn't
> that true of any tool? And isn't it true that the more you work with your
> tools the more skilled you become?
>=20
> RR
>=20
>=20
>=20
> John Britt says:
> >Now don=92t miss the point, I understand the value of UMF and see that i=
t
> >has a very valuable place in ceramics. It can help us to understand glaz=
es
> >and adjust them with great ease. It can help us to target our testing wh=
en
> >materials go out of production or are no longer available. But it does n=
ot
> >account for many, many other things that are critical to the outcome of
> >the glaze. There is not substitute for empirical testing, as I am sure R=
on
> >will agree.
>=20
> Ron Roy
> RR#4
> 15084 Little Lake Road
> Brighton, Ontario
> Canada
> K0K 1H0
> Phone: 613-475-9544
> Fax: 613-475-3513=20
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John Britt on tue 21 feb 06
Tom,
As you know I owe you a great deal for helping me with my book and I also
owe you and Ron a great deal for all your wonderful posts, on clayart.
And , of course, discussions are about ideas not personalities.
I agree that glaze calculation is a marvelous tool.
Nevertheless, I think what happens with computers and using Seger=92s
Formula is that people think it is a panacea which can answer all the
questions in a simple calculation. Sort of like the Wizard of Oz. But we
must remember that behind the curtain there is still a person.
It is a tool, which may elucidate and speed the process, but it is only
with empirical testing that the glaze can be found. This is because the
Seger Formula does not account for the clay body, the firing atmosphere,
firing and cooling cycle, the thickness of the glaze, the solubility of
materials, mesh size, the clay/glaze interface, variation in materials,
inaccuracy in analysis, etc.
In the 28,000 of firing clay only the last 110 or so has had the Seger
Formula. So for 27,000 years empirical testing has ruled the day and
produced fantastic results. The Sung Dynasty is only one example.
After reading your post I am reminded of the card catalogue that used to
exist in libraries. (Evidence of my advancing age) When you would look up
a book you would find all kinds of other books just by virtue of the
search method. I think the same is true of glaze testing. Often when we
test, line blends, or Currie method, etc. we find numerous other glazes
that we weren=92t even looking for. And we can learn volumes by observing
these results. But using computers, although we find the glaze we think we
want quickly we are eliminating many other interesting choices along the
way.
I am not saying that is it not a good tool, but that it is only ONE TOOL.
Empirical testing gives the final answer and there are many OTHER VERY
GOOD TOOLS!
Best to you and hope you are well!
John Britt
www.johnbrittpottery.com
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