Wes Rolley on tue 4 jan 05
I have been doing some reading and was intrigued by the following comment from Harry Fraser's "The Electric Kiln" (p. 90 in 2000 reprint).
"Matt glazed, zircon opacified glazes and various other crystalline glazes are produced by the development of crystals which precipitate from the glaze solution as the glaze cools."
While I have understood the need for slow cooling or firing down with matte and crystalline (macro or micro) glazes, this is the first reference that I have found which mentions it when zircon is used as an opacifiers. It make me go back to the archives where I found commentary by Michael Banks about the problems of zircon as an opacifier and the two, together, make sense. I just wonder why this fact was not mentioned in other books that I have read. In "Mastering Cone 6 Glazes" I find a reference to zircon and glaze stability. I wonder how much their results are affected by slow cooling.
It sound like some tests are in order.
Wes
Wesley C. Rolley
17211 Quail Court
Morgan Hill, CA 95037
(408)778-3024
"Why should we not be able to do what others have done before us? The answer must be that art is created not by human wisdom or intellect, but by human character as it is shaped by the times." Kitaoji Rosanjin.
Wesley C. Rolley
17211 Quail Court
Morgan Hill, CA 95037
(408)778-3024
"Why should we not be able to do what others have done before us? The answer must be that art is created not by human wisdom or intellect, but by human character as it is shaped by the times." Kitaoji Rosanjin.
John Hesselberth on tue 4 jan 05
On Tuesday, January 4, 2005, at 02:38 PM, Wes Rolley wrote:
> I just wonder why this fact was not mentioned in other books that I
> have read. In "Mastering Cone 6 Glazes" I find a reference to zircon
> and glaze stability. I wonder how much their results are affected by
> slow cooling.
Hi Wes,
I'm not sure I understand your question, but zircon is not needed to
make matte glazes. Running up the alkaline earth level will do a great
job of matting a glaze if you give time for the crystals to precipitate
out during cooling. You can also do it by using a high alumina level. I
suppose zircon could serve as a seed to give faster crystallization,
but so can titania or most anything else that has limited solubility in
the glaze melt.
Regards,
John
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
Wes Rolley on tue 4 jan 05
At 06:07 PM 1/4/2005, you wrote:
>I'm not sure I understand your question, but zircon is not needed to
>make matte glazes.
I was reacting to several things. First, zircon is widely named as an
opacifier. However, the quotation from Fraser's book is the first time I
have seen its effectiveness related to the practice of slow cooling or
firing down. If that is the case, then those recipes that use zircon could
possibly get by with less Zircopac (or whatever source) if one would slow
down the cooling.
I was also wondering if this was such common knowledge that no one bothered
to mention it.
It seems to be, in effect, the same mechanism at work...the crystaline
structures precipitating out during cooling. The quote from Fraser listed
a series of things that benefitted from slow cooling, matte and crystalline
glazes are two of them. Zircon as an opacifier is the other.
Wes
"Anytime you have an opportunity to make things better and you don't, then
you are wasting your time on this Earth" Roberto Clemente
Wes Rolley
http://www.refpub.com/
Ivor and Olive Lewis on wed 5 jan 05
Dear Wes Rolley,
Interesting questions which deserves deep thought. I say this because
I believe there is neither a simple nor a singular answer.
Once you get more than four oxides collaborating; eg
K2O-CaO-Al2O3-SiO2, to make a glaze the potential for combinations of
crystalline compounds starts to escalate towards infinity under the
influence of differing cooling rates.
But before you make any attempt to reach a defining answer you must
prove that all of the ingredients have become constituents of the
vitreous fluid prior to cooling.
Something worthy of consideration in relationship to the genesis of
strongly crystalline glazes, especially those which incorporate Potash
felspars, is the degree to which crystal precipitation increases the
concentration of Group 1 alkali oxides in the glass phase, causing a
subsequent deterioration in corrosion resistance of a glaze. This may
be of concern in Lime Felspar and Dolomite Felspar glazes which are
cooled slowly to cause matness and opacity through the deposition of
Wollastonite, Anorthite, Enstatite or Cordierite crystals within the
glass matrix.
I think many Clayart pals will consider this to be one of those things
best put in the "To Hard Basket"
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Wes Rolley on thu 6 jan 05
At 10:51 AM 1/6/2005, you wrote:
>Wes,
> Zircon opacifies mainly because it does not melt very well in a
> glaze. It does have some solubility, especially at C10 and above. For
> all practical purposes, though, the opaque nature of ziron-opacified
> glazes is due to relicts of the zircon left behind. While zircon may
> crystallize from the glaze melt, what I think is at work is just unmelted
> zircon.
I am not sure why I was intrigued by this question. I have rarely used
zircon anything and that was before I learned about slow cooling.
I note from Michael Banks
(http://lsv.ceramics.org/scripts/wa.exe?A2=ind0006&L=CLAYART&P=R25924) that:
The fact that tin and zirconium make good opacifiers in glazes, may be
due to the fact that both elements are known to exhibit high crystal field
stabilisation energies. The crystal field stabilisation energy of a
transition element varies from high (e.g. zirconium) to low (e.g. zinc) and
controls the potential of transition metals to occupy octahedral sites in
crystals. Zircon crystals (zirconium silicate) crystallise early out of
natural magmas at high temperatures and resist dissolution in glazes to a
great extent.
So you are probably right.
In another post,
(http://lsv.ceramics.org/scripts/wa.exe?A2=ind0201B&L=CLAYART&P=R22498) he
states that Zircon can also inhibit crazing:
The opacifier zircon (zirconium silicate) does this in three possible ways:
(1) the suspended crystals blocking crack propagation
(2) the low CTE of the undissolved zircon crystals
(3) dissolution of a % of the Zr changing the CTE/TS of the glass
So much to learn and so little time.
"Anytime you have an opportunity to make things better and you don't, then
you are wasting your time on this Earth" Roberto Clemente
Wes Rolley
http://www.refpub.com/
Dave Finkelnburg on thu 6 jan 05
Wes,
Zircon opacifies mainly because it does not melt very well in a glaze. It does have some solubility, especially at C10 and above. For all practical purposes, though, the opaque nature of ziron-opacified glazes is due to relicts of the zircon left behind. While zircon may crystallize from the glaze melt, what I think is at work is just unmelted zircon.
Other methods of obtaining glaze opacity include use of light refracting colorant oxides, freezing bubbles in the glaze, achieving phase separation--either with or without a crystal phase--in the glaze bulk, and growing crystals on the glaze surface. The latter is what happens in matt glazes.
Good potting!
Dave Finkelnburg
---------------------------------
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Ron Roy on thu 6 jan 05
Hi Wes,
Many glazes recrystallize without slow cooling - but they need to be built
that way.
What is significant about slow cooling is - many glazes that would
otherwise be glossy - will recrystallize if cooled slower.
I am amazed at how long the "effect" was not understood by so many authors
and potters.
By the way - there is a zircon matte in our book - page 106 we call a cone
6 Majolica.
RR
>I have been doing some reading and was intrigued by the following comment
>from Harry Fraser's "The Electric Kiln" (p. 90 in 2000 reprint).
>
>"Matt glazed, zircon opacified glazes and various other crystalline glazes
>are produced by the development of crystals which precipitate from the
>glaze solution as the glaze cools."
>
>While I have understood the need for slow cooling or firing down with
>matte and crystalline (macro or micro) glazes, this is the first reference
>that I have found which mentions it when zircon is used as an opacifiers.
>It make me go back to the archives where I found commentary by Michael
>Banks about the problems of zircon as an opacifier and the two, together,
>make sense. I just wonder why this fact was not mentioned in other books
>that I have read. In "Mastering Cone 6 Glazes" I find a reference to
>zircon and glaze stability. I wonder how much their results are affected
>by slow cooling.
>
>It sound like some tests are in order.
>
>Wes
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Louis Katz on wed 12 jan 05
I am awaiting my copy of the NCECA journal from last year so I can read
the article on robust matt glazes. I think it will clarify many
questions about calcium matt glazes.
Louis
>
> be of concern in Lime Felspar and Dolomite Felspar glazes which are
> cooled slowly to cause matness and opacity through the deposition of
> Wollastonite, Anorthite, Enstatite or Cordierite crystals within the
> glass matrix............
> Ivor Lewis.
> Redhill,
> S. Australia.
Ivor and Olive Lewis on thu 13 jan 05
Dear Louis Katz,
Did you get to the lecture ?
Why has it taken so long for the NCECA to step up to the line with
publication?
Perhaps "Robust Matt Glazes are those that lie thick on the clay
without descending with the force of gravity, very viscous.
Look forward to your summary.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Louis Katz on fri 14 jan 05
Hi Ivor,
Yes I was at the lecture. It was about mapping the phases and
appearance of a range of unity formula to attempt and determining a
region or formula that would always make matt glazes regardless of
cooling rate, and also being tolerant of slight differences in
formulation. It was very good.
Several hurdles face NCECA when it comes to getting its publications
out in a timely matter.
1. The presentors often don't meet deadlines.
2. The chair of publications is a voluntary position and putting the
thing together takes a long time if you are using "spare" time.
That said, I would prefer giving up on print and going to CD and online
publication.
I wish I had notes. I ran into the lecture, I was working on my pipe
organ, listened and left and forgot to bring anything I could use to
take good notes. The lecture was by a student of a professor at Alfred
(Ceramic Engineering) whose name I can't get into the front of my mind.
He gave a great lecture on plasticity and deformation of porcelain
bodies. It was based on research and was fascinating. I look forward to
having it in print as well.
Louis
On Jan 13, 2005, at 12:01 AM, Ivor and Olive Lewis wrote:
> Dear Louis Katz,
> Did you get to the lecture ?
> Why has it taken so long for the NCECA to step up to the line with
> publication?
> Perhaps "Robust Matt Glazes are those that lie thick on the clay
> without descending with the force of gravity, very viscous.
> Look forward to your summary.
> Best regards,
> Ivor Lewis.
> Redhill,
> S. Australia.
>
> _______________________________________________________________________
> _______
> 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.
>
>
http://www.tamucc.edu/wiki/Katz/HomePage
Ivor and Olive Lewis on sat 15 jan 05
Dear Louis,
The Whiteware person at Alfred is Prof William Carty. I have read the
Whiteware Papers. They are available from ACS.
I would like to see a phase diagram for a seven dimensional system
(Al2O3, SiO2. K2O, CaO, MgO, ZrO2 and Temperature) that might reveal
the location of a region which will always precipitate, even with
precipitous cooling rates. Ill 966 in the ACS Phase diagram book
(1974) gives a tantalising glimpse but no real guidance. The research
report should be good reading.
.
Regarding publication of the annals of the NCECA : Putting them on CD
or DVD seems a great idea that might be put to the Executive before
the next conference starts. If these things are not documented and
brought into the public domain then, even with 5000 plus delegates, I
would suggest that there may be a failure of purpose.
Only wish I could afford to attend.
Best regards,
Ivor
Louis Katz on sat 15 jan 05
I will suggest it Ivor if I am at one of the open meetings. I think
that the organization needs an electronic publications position on the
board. I do not think that any of the excellent publications people are
the people for this job and their job is already too big. How you
intend to "see" this seven dimensional system I do not know, I have a
hard enough time living in three, although I do often deal with time/
money/ place relationships that might be seen as five dimensional
matrices. I don't see myself as good at these things.
As always I suggest that someone from Clayart run as a DAL to NCECA. It
is possible as a Clayarter to get alot done on the board because you
have means of communicating with a bunch of members. Also mail from the
membership does shape policy, I think the board is responsive. I have
not read any rants about NCECA this year. I would suggest however that
any one who thinks NCECA should reserve more rooms spend some time
talking with the conference planner about her limitations. Don't try to
do it the first two days of the conference. She will be too busy.
Reservations of rooms is risky. If they do not fill NCECA is
responsible for them. It is a risk management decision in part I am
sure.
Louis
KE5CVK
contactable on:
146.780 mhz
IRLP node 3499 around dinner time in Texas
Echolink nearing midnight
On Jan 14, 2005, at 6:48 PM, Ivor and Olive Lewis wrote:
> Dear Louis,
> The Whiteware person at Alfred is Prof William Carty. I have read the
> Whiteware Papers. They are available from ACS.
> I would like to see a phase diagram for a seven dimensional system
> (Al2O3, SiO2. K2O, CaO, MgO, ZrO2 and Temperature) that might reveal
> the location of a region which will always precipitate, even with
> precipitous cooling rates. Ill 966 in the ACS Phase diagram book
> (1974) gives a tantalising glimpse but no real guidance. The research
> report should be good reading.
> .
> Regarding publication of the annals of the NCECA : Putting them on CD
> or DVD seems a great idea that might be put to the Executive before
> the next conference starts. If these things are not documented and
> brought into the public domain then, even with 5000 plus delegates, I
> would suggest that there may be a failure of purpose.
> Only wish I could afford to attend.
> Best regards,
> Ivor
>
> _______________________________________________________________________
> _______
> 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.
>
>
KE5CVK
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