Pat Walker on tue 1 jan 08
The following recipe is a cone 10 glaze can someone help to convert it to a
cone 6 glaze?
nepheline syenite 57.93
dolomite 19.13
zircopax 14.51
ball clay 3.90
red iron oxide 0.91
bentonite 3.63
Ron Roy on fri 4 jan 08
Hi Pat,
Best way would be to add zinc oxide unless you plan to fire the cone 6 in
reduction. Try adding 8, 10 and 12 zinc. This keeps the ratio the same so
it will still be a clay matte. 200 gram test batches should show you which
amount to use.
This also means it will still be short of silica so it's not going to be a
durable glaze - matte glazes are not the best choice as liner glazes
anyway.
Make sure it's fired in strict oxidation - zinc oxide is easily reduced and
the metal boils producing pin holes. Fire with a vent running or some way
to let in plenty of oxygen.
It may be possible to make it more durable with more silica - but you would
need to slow cool it to get the matte finish.
If you are looking for a durable matte glaze you might consider a high
calcium matte.
RR
>The following recipe is a cone 10 glaze can someone help to convert it to a
>cone 6 glaze?
>nepheline syenite 57.93
>dolomite 19.13
>zircopax 14.51
>ball clay 3.90
>red iron oxide 0.91
>bentonite 3.63
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Ivor and Olive Lewis on sat 5 jan 08
Dear Ron Roy,=20
You make the following suggestion << you plan to fire the cone 6 in =
reduction. Try adding 8, 10 and 12 zinc.>>
Perhaps you would explain the rational behind this procedure. What =
causes a refractory oxide with a melting point in excess of 1900 Deg C =
to induce a cone 10 glaze to reduce its maturity point by four cones ?
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Ron Roy on sun 6 jan 08
Hi Ivor,
Your have misquoted me - I said "UNLESS you plan to fire the cone 6 in
reduction ............."
Your habit of not including at least part of the post you are responding to
has some disadvantages.
It's an important distinction because in reduction the zinc oxide would be gone.
Unless you use boron, a frit or zinc you are going to have a hard time
getting cone 6 glazes to melt.
Look at the cone 6 UK glazes - they are mostly zinc fluxed - and so are the
bristol glazes. The melting point of an oxide is an unreliable indication
of it's usefulness as a flux in glazes.
See page 98 in our book - the zinc semi matte is a good example.
RR
>Dear Ron Roy,
>
>You make the following suggestion << you plan to fire the cone 6 in
>reduction. Try adding 8, 10 and 12 zinc.>>
>
>Perhaps you would explain the rational behind this procedure. What causes
>a refractory oxide with a melting point in excess of 1900 Deg C to induce
>a cone 10 glaze to reduce its maturity point by four cones ?
>
>Best regards,
>
>Ivor Lewis.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Ivor and Olive Lewis on mon 7 jan 08
Sorry about the confusion Ron.
Yes, to retain the context "Unless" is essential. Perhaps it might
have helped if you had given the additional information you have now
suggested (and I cut and paste)
.... << Unless you use boron, a frit or zinc you are going to have a
hard time getting cone 6 glazes to melt. >>....
Well the behaviour of compounds of Boron or a Frit is readily
explicable, they melting points lower than the intended maturity
temperature and high powers of solvation. They form a liquid below the
maturity point of the glaze and assist in dissolving refractory
compounds. But does Zinc oxide works work in this way ?
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Sent: Monday, 7 January 2008 6:49
Subject: Re: changing a cone 10 glaze to cone 6
> Hi Ivor,
>
> Your have misquoted me - I said "UNLESS you plan to fire the cone 6
in
> reduction ............."
>
> Your habit of not including at least part of the post you are
responding to
> has some disadvantages.
>
> It's an important distinction because in reduction the zinc oxide
would be gone.
>
> Unless you use boron, a frit or zinc you are going to have a hard
time
> getting cone 6 glazes to melt.
>
> Look at the cone 6 UK glazes - they are mostly zinc fluxed - and so
are the
> bristol glazes. The melting point of an oxide is an unreliable
indication
> of it's usefulness as a flux in glazes.
>
> See page 98 in our book - the zinc semi matte is a good example.
>
> RR
>
>
> >Dear Ron Roy,
> >
> >You make the following suggestion << you plan to fire the cone 6 in
> >reduction. Try adding 8, 10 and 12 zinc.>>
> >
> >Perhaps you would explain the rational behind this procedure. What
causes
> >a refractory oxide with a melting point in excess of 1900 Deg C to
induce
> >a cone 10 glaze to reduce its maturity point by four cones ?
> >
> >Best regards,
> >
> >Ivor Lewis.
>
> Ron Roy
> RR#4
> 15084 Little Lake Road
> Brighton, Ontario
> Canada
> K0K 1H0
>
>
John Hesselberth on mon 7 jan 08
On Jan 6, 2008, at 10:14 PM, Ivor and Olive Lewis wrote:
> They form a liquid below the
> maturity point of the glaze and assist in dissolving refractory
> compounds. But does Zinc oxide works work in this way ?
Hello Ivor,
Well it seems to work in Europe--I guess it would in the U.S. and
Australia also. Use of boron to get a glaze to melt at cone 6 is much
less common in Europe than in the states. Zinc is the flux of choice.
Certainly the famous Bristol glazes are fluxed with zinc and there
are lots of Bristol-type glazes that melt at cone 6.
What makes you think a "flux" has to itself melt before it can lower
the melting point of a glaze? Can it not dissolve in what is already
molten? Calcium oxide does not melt at firing temperatures--not even
at cone 10 where neither zinc nor boron are commonly used. Nor do
magnesium oxide or strontium carbonate or oxide, yet they serve as
fluxes. For that matter the Handbook of Chemistry and Physics says
that sodium oxide does not melt at all but sublimes at 1275C--above
cone 6. Is it not a flux at cone 6? You need a different hypothesis.
In fact you have already proposed such a hypothesis by suggesting
that trace amounts of NaCl are the first thing to melt and serve as
the solvent for the rest. Once a material gets into solution its
melting point is totally irrelevant I would think.
Regards,
John
John Hesselberth
www.frogpondpottery.com
"Man is a tool-using animal....without tools he is nothing, with
tools he is all" .... Thomas Carlyle
Steve Slatin on mon 7 jan 08
Interesting point, John. Perhaps if Ivor were to
refer to a PHASE DIAGRAM to identify the
relevant EUTECTOID he would find the answer.
John Hesselberth wrote:
Well it seems to work in Europe--I guess it would in the U.S. and
Australia also.
---------------------------------
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May Luk on mon 7 jan 08
Hello all;
M. Bailey has stated in his popular Glaze Cone 6 book that zinc is cheaper to use than boron frit. That's why most of his recipes contain zinc oxide. I am UK trained, therefore most of my recipes contain zinc oxide even I am now in the US using US materials.
I was close reading on Glazes Cone 6 and Mastering Cone 6 Glazes and I could see material preferences with different potters. I always wonder which material was 'better' and when to use boron frit over zinc. I have done some line blend exchanges on a few glazes and I found zinc oxide to be a stronger flux. However, the color and the texture of the glaze came out differently. (Isn't that always the case!! :-))
I have done enough Currie Grids to see that there is no such thing as lowering cone temperature in a straight forward fashion. Then again, I am pedantic when it comes to glaze learning.
Regards
May
Kings County
[...]Well it seems to work in Europe--I guess it would in the U.S. and
Australia also. Use of boron to get a glaze to melt at cone 6 is much
less common in Europe than in the states. Zinc is the flux of choice.
Certainly the famous Bristol glazes are fluxed with zinc and there
are lots of Bristol-type glazes that melt at cone 6.[...]
John Hesselberth
Steve Slatin on tue 8 jan 08
I believe if you search the archives, you will find
that "phase diagram," "eutectic" and "eutectiod"
appear frequently in your postings. Perhaps you
could provide the definition for each that you
use for each and answer your own question?
-- Steve S
Ivor and Olive Lewis wrote:
Dear Steve Slatin ,
An intriguing response........
>
....providing the necessary ingredients that contribute to creation of a eutectoid reaction pre-exist in the system under observation, a caveat that also applies to Eutectic Reactions.
Perhaps you would like to define the term "Eutectoid", with Ceramic examples, for the edification of other readers.
Best regards, and thanks for joining in.
Ivor Lewis.
---------------------------------
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Ivor and Olive Lewis on tue 8 jan 08
Dear Steve Slatin ,
An intriguing response........
<DIAGRAM to identify the
relevant EUTECTOID he would find the answer.>>
....providing the necessary ingredients that contribute to creation of a =
eutectoid reaction pre-exist in the system under observation, a caveat =
that also applies to Eutectic Reactions.
Perhaps you would like to define the term "Eutectoid", with Ceramic =
examples, for the edification of other readers.
Best regards, and thanks for joining in.
Ivor Lewis.
Redhill,
South Australia.
Ivor and Olive Lewis on wed 9 jan 08
Dear May Luk,
Thank you for your contribution to this thread. I have not read the book =
you mention but no doubt Zinc oxide as a raw ingredient is lower in =
price, unit for unit, than a ceramic frit though I seldom use it because =
my firings are usually done with a reducing atmosphere.
And I agree with you, Zinc Oxide is a powerful flux. Those who employ it =
to develop their wonderful crystalline glazes are aware of this. Those =
materials are so fluid much of the just runs from the pot surface.
Originally, recipes for Zinc crystal glazes, such as those given by =
Herbert Sanders, required temperature as high as Cone 15 to liquefy. In =
recent times, it has been shown that firing temperatures for glazes =
containing as much as 25% Zinc oxide can be brought down to Cone 6 by =
using frits. It was this fact that caused me to ask Ron Roy about the =
behaviour of Zinc oxide. There seemed to be a contradiction or an =
anomaly in the proposed technology to reduce the maturity temperature of =
a glaze by adding Zinc Oxide.=20
Perhaps you could explain.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Ivor and Olive Lewis on wed 9 jan 08
Dear John Hesselberth,=20
Good to hear from you again.
As I read the history of ceramics, Bristol Glazes were deliberately =
designed to get a surface finish that had the optical brilliance of =
Glazes based on Lead oxide without exposing workers to toxic materials.
The case under discussion involves the adjustment of a pre-existing =
glaze to reduce its maturity temperature.
You tell me <can lower the melting point of a glaze? Can it not dissolve in what is =
already molten? Calcium oxide does not melt at firing temperatures--not =
even at cone 10 where neither zinc nor boron are commonly used. Nor do =
magnesium oxide or strontium carbonate or oxide, yet they serve as =
fluxes.>>
I think grouping Alkali Metal and Alkali Earth materials into a single =
group under the heading of "Flux" prevents us from discriminating =
between their individual activities as glaze ingredients. The concepts =
you infer in you statement are those things I would like to see =
clarified.
<< For that matter the Handbook of Chemistry and Physics says that =
sodium oxide does not melt at all but sublimes at 1275C=97above cone 6. =
Is it not a flux at cone 6? You need a different hypothesis.>>
We must have differing editions of the CRC Handbook of Chemistry and =
Physics. I have Sodium Oxide, Na2O as decomposing at 1132 Deg Celsius. =
Kaye and Laby, "Tables of Physical and Chemical Constants" agrees with =
you. Durrant, "General and Inorganic Chemistry" describes it as a white =
amorphous powder which decomposes at 400 deg C into sodium peroxide and =
sodium, that it combines with water with extreme violence to form Sodium =
hydroxide. There is a second oxide, Sodium Peroxide Na2O2 which forms =
when Sodium metal burns in air. This will react instantly with water =
vapour and Carbon dioxide forming Sodium hydroxide and Sodium Carbonate. =
I am unsure as to the reason you invoke Sodium oxide. I have never seen =
a glaze recipe where it features as an ingredient. Soda Ash, yes. Soda =
Felspar, yes. Sodium Carbonate, yes. But never Sodium Monoxide. As I =
understand thing "Na2O" is used conventionally in the Seger and Unity =
formulae as an abstracted element.
<trace amounts of NaCl are the first thing to melt and serve as the =
solvent for the rest. Once a material gets into solution its melting =
point is totally irrelevant I would think.>>
To that I would add that there is also the possibility that when a =
Felspar is an ingredient then there is the potential for an Alkali Metal =
Carbonate to form over time when the glaze batch is mixed with water. =
When these carbonates melt they can be quite aggressive towards =
silicates as temperature rises. The amounts may be minute but there =
presence could be significant.
Best regards,
Ivor
May Luk on wed 9 jan 08
Dear Ivor;
Happy New Year!
Thank you for the having the confidence in me that I can explain the anomaly in the propose technology about lowering glaze temperature with Zinc Oxide. Unfortunately I cannot rise to the challenge. Most clay-artworkers are cut off from industrial grade ceramic technologies. It is not the scope of our normal clay learning. I welcome the convergence between faith and science when an explanation is not readily available.
Thanks and best regards
May
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
[...]about the behaviour of Zinc oxide. There seemed to be a contradiction or an anomaly in the proposed technology to reduce the maturity temperature of a glaze by adding Zinc Oxide.
Perhaps you could explain.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Ivor and Olive Lewis on thu 10 jan 08
Dear Steve Slatin,
<diagram," "eutectic" and "eutectiod" appear frequently in your postings. =
Perhaps you could provide the definition for each that you use for each =
and answer your own question? >>
If I have used those terms so many times it would be superfluous to =
reiterate the information. But out of curiosity, how many times have I =
invoked the Eutectoid reaction in a ceramic context?
Enjoy your weekend.
Best regards,
Ivor
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