Ivor and Olive Lewis on wed 21 jul 04
Dear Ron Roy,
In a recent post you said "...and alumina is a crystal inhibitor -
which explains why crystal glazes tend to run so much."
Perhaps you would explain why this is so.
I ask because it seems to contradict the results of a recent test
series where I loaded a cone 8 transparent high Soda felspar glaze
with Zinc Oxide. When fired and cooled to a holding temperature
typical of the system recommended in books about crystal glazes
the results were glazes with a profusion of typical but small
Willemite crystals. This seems to contradict our popular understanding
of the process. Nor, as might be expected from the way we consider the
fluxing action of Zinc, did the viscosity decrease. These glazes did
not flow freely into the catchers.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
John Britt on thu 22 jul 04
Ivor,
Try leaving the alumina out of the glaze and test that. You will probably
see much larger crystals,
John
De Ruyter Jean on thu 22 jul 04
Ivor
Keep in mind that the max. temperature is of a great importance in relati=
on
with the
Al=B2O=B3.
If You want to see some results have a look at www. crystallineglazes.be
If I can be of any help Jderuyter@pondora.be
Jan
----- Original Message -----
From: "John Britt"
To:
Sent: Thursday, July 22, 2004 1:33 PM
Subject: Re: Inhibition of Crystallisation
> Ivor,
>
> Try leaving the alumina out of the glaze and test that. You will probab=
ly
> see much larger crystals,
>
> John
>
>
_________________________________________________________________________=
___
__
> 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
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>
>
william schran on thu 22 jul 04
Ivor wrote:>Dear Ron Roy,
In a recent post you said "...and alumina is a crystal inhibitor -
which explains why crystal glazes tend to run so much."
Perhaps you would explain why this is so.
I ask because it seems to contradict the results of a recent test
series where I loaded a cone 8 transparent high Soda felspar glaze
with Zinc Oxide. When fired and cooled to a holding temperature
typical of the system recommended in books about crystal glazes
the results were glazes with a profusion of typical but small
Willemite crystals. This seems to contradict our popular understanding
of the process.<
It's true that one may have a glaze containing zinc and sufficient
alumina to form a "stable" glaze and still achieve crystals as a
result of firing, or in some cases layering of glazes, but the
resulting crystals will remain rather small.
Fara Shimbo as done some tests of adding increasing amounts of
alumina to crystalline glazes and still achieved satisfactory macro
crystals. But there is an upper limit of the amount of refractory
materials that could be added and still get large crystals.
I worked with a few glazes several years ago, firing at cone 6. One
of the glazes is a wonderful mat glaze containing about 15% zinc.
When layered over other glazes, the glaze would become transparent
and form many small willemite crystals without any special
cooling/holding of temperature.
All that said, to achieve large macro crystals, a break down of the
lattice structure of the glassy matrix is necessary to allow glaze
movement resulting in the attraction of positive and negative ions of
zinc and silica to form the crystals. Additions of alumina to the
extent that would inhibit the glaze movement would impact the size of
the crystals.
Bill
David Beumee on thu 22 jul 04
Great William!
So, do you have a cone 10 base that'll work in reduction to get me started?
David Beumee
Earth Alchemy Pottery
Lafayette, CO
> Ivor wrote:>Dear Ron Roy,
> In a recent post you said "...and alumina is a crystal inhibitor -
> which explains why crystal glazes tend to run so much."
> Perhaps you would explain why this is so.
> I ask because it seems to contradict the results of a recent test
> series where I loaded a cone 8 transparent high Soda felspar glaze
> with Zinc Oxide. When fired and cooled to a holding temperature
> typical of the system recommended in books about crystal glazes
> the results were glazes with a profusion of typical but small
> Willemite crystals. This seems to contradict our popular understanding
> of the process.<
>
> It's true that one may have a glaze containing zinc and sufficient
> alumina to form a "stable" glaze and still achieve crystals as a
> result of firing, or in some cases layering of glazes, but the
> resulting crystals will remain rather small.
>
> Fara Shimbo as done some tests of adding increasing amounts of
> alumina to crystalline glazes and still achieved satisfactory macro
> crystals. But there is an upper limit of the amount of refractory
> materials that could be added and still get large crystals.
>
> I worked with a few glazes several years ago, firing at cone 6. One
> of the glazes is a wonderful mat glaze containing about 15% zinc.
> When layered over other glazes, the glaze would become transparent
> and form many small willemite crystals without any special
> cooling/holding of temperature.
>
> All that said, to achieve large macro crystals, a break down of the
> lattice structure of the glassy matrix is necessary to allow glaze
> movement resulting in the attraction of positive and negative ions of
> zinc and silica to form the crystals. Additions of alumina to the
> extent that would inhibit the glaze movement would impact the size of
> the crystals.
>
> Bill
>
> ______________________________________________________________________________
> 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.
Ivor and Olive Lewis on fri 23 jul 04
Dear John,
Eliminating the Alumina from the recipes would defeat the purpose of
my investigation.
With what would I replace 65% Felspars in a perfectly adequate
transparent Cone 8 glaze which fits the clay I am using without
crazing, other than by using some manufactured frit which might give
me the Alkali content I desire and eliminate the Alumina. Then it
would introduce into the mixture other, as far as my investigation
goes, undesirable elements such as Boron.
In addition, your concept disregards conditions of firing which can
have a major effect on the development of crystals. Or is my
understanding of the process up the creek?
The question still stands, "Why are we told Alumina suppresses crystal
formation", I would assert that though this may be true in some
circumstances it could be false in many other instances. If I am to
believe what is said about the effects of Alumina I wish to know about
chemical &/or thermodynamic processes which leads to this result.
But you were right to make the suggestion.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Ivor and Olive Lewis on fri 23 jul 04
Dear Jean De Ruyter,
Not only that, the form in which the alumina is incorporated into the
recipe has an influence.
The major proportion of Al2O3 in this base glaze is as a felspar
mixture together with a small proportion of Kaolin. But the glaze is a
reliable cone 8 transparent high gloss glaze and individual Zinc
Silicate crystals grow to over five mm diameter.
In Studio Ceramic Technology there is a tendency to use generalised
statements as valid facts. However, when these statements are tested,
they are found to have at least some degree of uncertainty or to be
invalid.
Thanks for your input.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
----- Original Message -----
From: "De Ruyter Jean"
To:
Sent: Friday, 23 July 2004 12:31
Subject: Re: Inhibition of Crystallisation
Ivor
Keep in mind that the max. temperature is of a great importance in
relation
with the
Al=B2O=B3.
If You want to see some results have a look at www.
crystallineglazes.be
If I can be of any help Jderuyter@pondora.be
Jan
----- Original Message -----
From: "John Britt"
To:
Sent: Thursday, July 22, 2004 1:33 PM
Subject: Re: Inhibition of Crystallisation
> Ivor,
>
> Try leaving the alumina out of the glaze and test that. You will
probably
> see much larger crystals,
>
> John
>
>
______________________________________________________________________
______
__
> 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.
>
>
______________________________________________________________________
________
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
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Ivor and Olive Lewis on fri 23 jul 04
Dear David Beumee,
Here we are, discussing Zinc Crystalline Glazes and it was recently
stated in absolute terms that Zinc Oxide is a no-no in a high
temperature reduction firing because of the reduction of the Zinc
Oxide to Metallic Zinc which boils away at 913=BA Celsius.
So why ask for a Cone 10 Base for reduction firing, unless you have
some magic potion which overcomes this deficiency. Reveal your
alchemical knowledge ! !
Now, I ask you. If Alumina suppresses crystallisation, how does it
achieve this?
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
.
william schran on fri 23 jul 04
Ivor wrote: as my investigation
goes, undesirable elements such as Boron. .....In addition, your
concept disregards conditions of firing which can have a major effect
on the development of crystals. Or is my understanding of the process
up the creek?<
The traditional crystalline glaze recipe is: sodium frit, zinc,
silica with additional materials added to nudge color, temperature
or specific types of crystal formations.
One of the folks from Fusion Frits presented a paper earlier this
year that suggested sodium played an integral role in the formation
of zinc orthosilicate crystals. Perhaps you may wish to concentrate
on using soda feldspars as part of your investigation.
I did a series of tests with some crystalline glaze recipes that were
producing good results. To each I added 2% of titanium dioxide,
lithium carbonate & gerstley borate. The additions have helped in the
formation of secondary crystals in the ground area (the area in which
the primary crystals are suspended). I'd also recommend adding 1/2%
titanium to your tests to help seed the crystals.
And yes, you are correct. You are not up the creek. It IS all about
the firing when it comes to crystalline glazes.
Bill
Earl Brunner on fri 23 jul 04
OK, maybe the assertion needs to be restated. Alumina inhibits LARGE
crystal growth. I've used a lot of glazes which will grow small crystals,
the idea behind crystalline matts. I just don't see many if any glazes
growing large crystals that have much alumina in them. So, are you saying
that you can grow large crystals in your glaze, along the lines of what we
would call a crystal glaze?
Warmest regards (it was 110+F. yesterday)
Earl Brunner
Las Vegas, NV
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Ivor and Olive
Lewis
Sent: Thursday, July 22, 2004 9:14 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Inhibition of Crystallisation
Dear John,
Eliminating the Alumina from the recipes would defeat the purpose of
my investigation.
With what would I replace 65% Felspars in a perfectly adequate
transparent Cone 8 glaze which fits the clay I am using without
crazing, other than by using some manufactured frit which might give
me the Alkali content I desire and eliminate the Alumina. Then it
would introduce into the mixture other, as far as my investigation
goes, undesirable elements such as Boron.
In addition, your concept disregards conditions of firing which can
have a major effect on the development of crystals. Or is my
understanding of the process up the creek?
The question still stands, "Why are we told Alumina suppresses crystal
formation", I would assert that though this may be true in some
circumstances it could be false in many other instances. If I am to
believe what is said about the effects of Alumina I wish to know about
chemical &/or thermodynamic processes which leads to this result.
But you were right to make the suggestion.
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.
Jim Murphy on fri 23 jul 04
Hi Ivor,
Interesting experiment.
As I understand your test series, you've added Zinc Oxide to your Cone 8
transparent high Soda feldspar glaze, fired and cooled to a holding
temperature typical of the system recommended in books about crystal glazes.
The resultant glazes had a profusion of small Willemite (Zinc Silicate)
crystals.
Some may say the lack of large (macro) crystals is due to the "beginning"
Alumina-level of your original transparent glaze recipe, i.e., too high.
I'll take a somewhat different "whack" at this one and perhaps become the
latest sacrificial lamb in the process.
I'm keying-in on your use of the word "transparent" for your high Soda
feldspar glaze - "transparent" prior to the addition of Zinc Oxide.
I wonder if your original glaze "transparency" was possibly indicative of
high-Alumina solubility. If the Alumina had not been taken completely into
solution, could the glaze become a transparent "glass"??? Your Alumina-level
in your well-fitting glaze must have been "just right". (In general, higher
Alumina-solubility yields better transparent "glass". Too much Alumina
restricts glass formation. Presumably, no additional Alumina entered with
the Zinc Oxide.)
In a recent Shino-related post, I mentioned how high-Alumina may limit the
formation of "glass" and also I asked rhetorically, "in a high-Alkali
high-Alumina high-Silica feldspathic Shino, does Alumina-solubility inhibit
crystal growth, or does crystal growth inhibit Alumina-solubility ..... ??"
What apparently has happened is that your once transparent glaze - or
"glass" if you'll allow - has now become more of a "glass-ceramic" material,
a combination of glass and crystalline phases.
In glass-ceramics, generally "crystals" grow INTO a surrounding "glass
phase". "Glass" is by definition non-crystalline.
Your test series - under controlled firing conditions - resulted in alot of
smaller crystals growing into glass as opposed to fewer larger (macro)
crystals growing into glass.
Ivor, you're asking, "Why are we told Alumina suppresses crystal
formation?". I dunno.
Perhaps - for your particular glaze recipe - the addition of Zinc Oxide has
restricted Alumina-solubility, suppressing NOT large crystal formation per
se, but rather, suppressing the AMOUNT of glass formed and allowing smaller
crystalline phases (Willemite) to grow wildly out-of-control depending, of
course, on your aesthetic perspective.
By the way, I understand nearly all Willemite crystals fluoresce a bright
green under ultra-violet light. Some may even glow (phosphoresce) after the
UV light is removed.
Best wishes,
Jim Murphy
Ron Roy on sat 24 jul 04
Hi Ivor,
Overloading with certain oxides will produce overall recrystalization - as
in oxides of Barium, Calcium, Magnesium, Strontium, Zinc - and Aluminium.
What I was talking about was the large single crystals. These glazes are
well know for sliding off pots - and the reason is the low amount of
alumina in the glaze which - if there in higher amounts - would inhibit the
crystals from forming. These types of crystals grow best in a glaze with a
a low viscosity.
The literature is full of references about alumina oxide being a crystal
inhibitor.
RR
>Dear Ron Roy,
>In a recent post you said "...and alumina is a crystal inhibitor -
>which explains why crystal glazes tend to run so much."
>Perhaps you would explain why this is so.
>I ask because it seems to contradict the results of a recent test
>series where I loaded a cone 8 transparent high Soda felspar glaze
>with Zinc Oxide. When fired and cooled to a holding temperature
>typical of the system recommended in books about crystal glazes
>the results were glazes with a profusion of typical but small
>Willemite crystals. This seems to contradict our popular understanding
>of the process. Nor, as might be expected from the way we consider the
>fluxing action of Zinc, did the viscosity decrease. These glazes did
>not flow freely into the catchers.
>Best regards,
>Ivor Lewis.
>Redhill,
>S. Australia.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ivor and Olive Lewis on sat 24 jul 04
Dear Jim Murphy,
I am working from the premise that a base glaze is mature when, after
firing, it presents as a transparent, high gloss surface on a pot.
This is the only indication I know of which suggests that all of the
materials entered the molten state, that highly refractory materials
have dissolved and that the result has the short dimensional order and
long range disorder typical of what is known as the Glassy or
Amorphous State described by Kingery et al and Brownell.
Now, if I do precisely as you say, that is add Zinc oxide to such a
composition, I will destabilise it when it is fired. That is not my
intention. If I do precisely as you say, I will destroy those
desirable qualities of the glaze I have chosen for this task. Those
qualities are High viscosity, Colour Response, Brightness and
Durability.
Results so far coming form the kiln give direction to future trials.
The Goal is a surface which is transparent except for the crystals and
a glaze which avoids the disadvantages of current Frit based recipes.
You say " By the way, I understand nearly all Willemite crystals
fluoresce a bright green under ultra-violet ". Some Museums show this
in their Earth Science displays. UV lamps are fairly cheap. Try Radio
Shack, or an electrical supplier.
In your inquiry about the nature of Shino you ask "...does
Alumina-solubility inhibit crystal growth, or does crystal growth
inhibit Alumina-solubility ..... ??". Perhaps in the case of the
former there would be no crystals whereas in the latter it would be
Sapphire or Ruby crystals which would accumulate in the glaze. In
either case there would be no Willemite
formations. Why not test your proposition?
By the way, there is not free Alumina in the composition I have chosen
for my work. It is only present in the abstract sense when the
composition is analysed and presented as a Unity Matrix. Failing to
make this distinction may have a bearing on some of the arguments
which are presented in the literature.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
----- Original Message -----
From: "Jim Murphy"
To:
Sent: Saturday, 24 July 2004 5:22
Subject: Re: Inhibition of Crystallisation
> Hi Ivor,
>
> Interesting experiment.
>
> As I understand your test series, you've added Zinc Oxide to your
Cone 8
> transparent high Soda feldspar glaze, fired and cooled to a holding
> temperature typical of the system recommended in books about crystal
glazes.
> The resultant glazes had a profusion of small Willemite (Zinc
Silicate)
> crystals.
>
> Some may say the lack of large (macro) crystals is due to the
"beginning"
> Alumina-level of your original transparent glaze recipe, i.e., too
high.
>
> I'll take a somewhat different "whack" at this one and perhaps
become the
> latest sacrificial lamb in the process.
>
> I'm keying-in on your use of the word "transparent" for your high
Soda
> feldspar glaze - "transparent" prior to the addition of Zinc Oxide.
>
> I wonder if your original glaze "transparency" was possibly
indicative of
> high-Alumina solubility. If the Alumina had not been taken
completely into
> solution, could the glaze become a transparent "glass"??? Your
Alumina-level
> in your well-fitting glaze must have been "just right". (In general,
higher
> Alumina-solubility yields better transparent "glass". Too much
Alumina
> restricts glass formation. Presumably, no additional Alumina entered
with
> the Zinc Oxide.)
>
> In a recent Shino-related post, I mentioned how high-Alumina may
limit the
> formation of "glass" and also I asked rhetorically, "in a
high-Alkali
> high-Alumina high-Silica feldspathic Shino, does Alumina-solubility
inhibit
> crystal growth, or does crystal growth inhibit Alumina-solubility
..... ??"
>
> What apparently has happened is that your once transparent glaze -
or
> "glass" if you'll allow - has now become more of a "glass-ceramic"
material,
> a combination of glass and crystalline phases.
>
> In glass-ceramics, generally "crystals" grow INTO a surrounding
"glass
> phase". "Glass" is by definition non-crystalline.
>
> Your test series - under controlled firing conditions - resulted in
alot of
> smaller crystals growing into glass as opposed to fewer larger
(macro)
> crystals growing into glass.
>
> Ivor, you're asking, "Why are we told Alumina suppresses crystal
> formation?". I dunno.
>
> Perhaps - for your particular glaze recipe - the addition of Zinc
Oxide has
> restricted Alumina-solubility, suppressing NOT large crystal
formation per
> se, but rather, suppressing the AMOUNT of glass formed and allowing
smaller
> crystalline phases (Willemite) to grow wildly out-of-control
depending, of
> course, on your aesthetic perspective.
>
> By the way, I understand nearly all Willemite crystals fluoresce a
bright
> green under ultra-violet light. Some may even glow (phosphoresce)
after the
> UV light is removed.
>
> Best wishes,
>
> Jim Murphy
>
>
______________________________________________________________________
________
> 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.
Ivor and Olive Lewis on sat 24 jul 04
Dear William Schran,
Thanks for your support
My reading of Crystal Glaze Technology is that, historically, recipes
were based on raw Sodium Silicate or Carbonate as solvents for Zinc
oxide, as illustrated in H. T. Sanders book "Glazes for Special
Effects. Unfortunately I do not have Parmellee and Harmer to check.
Since Anhydrous Sodium Di-Silicate melts 874=BA C and Sodium Carbonate
(a known HT solvent for stubborn materials) melts in the 800's, I can
understand both being chosen to dissolve Zinc Oxide in a glaze recipe.
It is interesting that the Sanders Raw Crystalline Glaze E.W,S # 2
(Cone 13-15) recipe contains 9% raw Alumina (Not as clay of in a
felspar)
Another point which demands consideration. When was it posited and Who
first said that "Alumina" should be minimised or deleted from a
Willemite Crystalline Glaze composition ? Someone must have this
knowledge in their college notes.
I am aware it is claimed that Titanium dioxide is recommended as a
good nucleating agent but 1/2 % of finely divided < 200# powder is
adding millions of fragments and I only want a few growths.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Ivor and Olive Lewis on sat 24 jul 04
Dear Earl,
Yes, the aim is to get large planar crystalline entities but to
overcome the fluidity problems. Those who go through the processes of
making coasters or setters and then cleaning up the bases will
appreciate what I am suggesting.
The few results I have had so far are suggestive of an need for better
temperature control and determination of precise temperatures at which
to nucleate and grow the crystals.
More information at my reply to Jim Murphy.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
John Britt on sat 24 jul 04
Ivor,
I believe zinc, the metal, melts at 410 F (786 C).
You might try to put a thin coat of a crystalline glaze (low alumina)
over your cone 10 glaze to take advantage of the stiff base without the
running.
John Britt
www.johnbrittpottery.com
On Fri, 23 Jul 2004 14:14:42 +0930, Ivor and Olive Lewis
wrote:
Metallic Zinc which boils away at 913=BA Celsius.
>Best regards,
>Ivor Lewis.
Ellie Blair on sat 24 jul 04
----- Original Message -----=20
From: Ivor and Olive Lewis=20
To: CLAYART@LSV.CERAMICS.ORG=20
Sent: Friday, July 23, 2004 11:36 PM
Subject: Re: Inhibition of Crystallisation
I am aware it is claimed that Titanium dioxide is recommended as a
good nucleating agent but 1/2 % of finely divided < 200# powder is
adding millions of fragments and I only want a few growths.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
_It is hard to control the amount of crystals you get on a pot. You =
can control the size by the soak times_and the number of crystals can =
also be somewhat controled. In order to get just a few large crystals =
on a pot the answer is seeding the crystals instead of depending on the =
zinc, titanium or any other seeding agent. This may be another avenue =
you can pursue. Another factor of unwanted nucelui can be controlled by =
sanding the surface either before you bisque or after if you bisque to =
08 or lower. Every raised surface on the surface can create a crystal =
and if you are trying to control the number of places for crystals to =
grow you need to make sure the surface of you pot is smooth. I use 200 =
grit silicon carbide wet/dry sandpaper.
Ellie Blair
Blair Pottery
Lawrence, Kansas 66047
=
_________________________________________________________________________=
___
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.
Jim Murphy on sat 24 jul 04
on 7/24/04 12:40 AM, Ivor and Olive Lewis at iandol@WESTNET.COM.AU wrote:
<< Now, if I do precisely as you say, that is add Zinc oxide to such a [base
glaze] composition, I will destabilise it when it is fired.>>
Hi Ivor,
Your reply indicates to me that my words have somehow been twisted around
some 180 degrees and put totally out-of-phase with my intended logic &
reasoning . (I think I hear "Where Is My Mind?" by 'The Pixies' playing in
the background!)
And here, I thought I was implying there may in fact be TOO MUCH Zinc Oxide
in the glaze and/or NOT ENOUGH glass formed to support LARGER CRYSTAL
growth. ('Capitals' used for emphasis only my friend.) Recall, I was taking
a "different 'whack'" to merely agreeing with those who suggest there may be
too much Alumina.
Perhaps the following is where things got miscontrued ? .... you wrote:
<< In your inquiry about the nature of Shino you ask "...does
<< Alumina-solubility inhibit crystal growth, or does crystal growth
<< inhibit Alumina-solubility ..... ??". Perhaps in the case of the
<< former there would be no crystals whereas in the latter it would be
<< Sapphire or Ruby crystals which would accumulate in the glaze. In
<< either case there would be no Willemite formations.>>
Ivor, I intended my rhetorical question to invoke questions like:
1. "Is it 'high' or 'low' Alumina-solubility which may inhibit crystal
growth?; and 2. "Can crystal growth decrease Alumina-solubility?
My answer to question "1." above is that 'low' Alumina-solubility (meaning
less Alumina is taken into solution) may indeed inhibit crystal growth
BECAUSE 'low' Alumina-solubility suppresses glass formation (I think in
terms of glass 'thickness' for visual purposes), so, there is LESS glass
(volume-wise) for LARGER crystals to grow into. Also, some growing crystals
- like Willemite (Zn2SiO4) - have apparently combined with Silica atoms,
Silica that could have gone into forming more glass thereby further limiting
LARGER CRYSTAL development.
[Some others may say a glaze "high in Alumina" MEANS the same thing as 'low'
Alumina-solubility --- I believe you'll agree, Ivor, Alumina-level and
Alumina-solubility are two entirely different parameters]
Also, my answer is "Yes" to question "2." above - especially in a
glass-ceramic material, i.e., crystal glaze. How's it work? Here is where
oxide-theorists and molten-soup-particle worlds collide my friend!
During firing, I picture highly-refractory relatively LARGE-SIZED ATOMS of
Alumina and Silica - some still-undissolved - in a surrounding molten glaze.
SMALLER atoms - like Zn, Na, K, etc. - are able to move more freely in the
molten glaze and combine with other atoms. Now - here is where my logic &
reasoning may be "different" from others with respect to LARGE CRYSTAL
development in crystal glazes - there may be crystals (perhaps smaller
crystals) growing at lower temperatures than you realize AND these growing
crystals may present a physical impediment, i.e., they [growing crystals] -
as well as large undissolved Silica atoms - get in the way of other mobile
atoms and limit the ability of the still-undissolved Alumina atoms to be
taken into solution. In effect, Alumina-solubility is LOWERED.
If my logic & reasoning is indeed something short of pure utter looniness -
and I hope it is - , then it's possible by simply DECREASING Zinc
Oxide - in your particular glaze recipe - you may overcome LOWERED
Alumina-solubility, form more glass - more viscous glass - and get those
larger planar crystals to grow without necessarily needing to adjust the
glaze firing schedule. [Less Zinc atoms in-the-mix may equal less
competition for Silica atoms which are needed to form more glass. And
perhaps, there'll be less smaller crystals formed early on and a more
favorable environment for larger crystal growth.]
Anyhow, that's my own theory of how 'low' Alumina-solubility - rather than
high Alumina-level - may suppress large crystal growth in Zinc crystalline
glazes.
That's my theory and I'm stickin' to it, although if somebody's got
something better - I'm all ears...
Best wishes,
Jim Murphy
Lyrics from "Where Is My Mind?" by 'The Pixies':
With your feet in the air and your head on the ground
Try this trick and spin it, yeah
Your head will collapse
But there's nothing in it
And you'll ask yourself
Where is my mind [3x]
Ivor and Olive Lewis on sun 25 jul 04
<alumina)
over your cone 10 glaze to take advantage of the stiff base without
the
running.>>
Not a bad idea John.
Perhaps that is what some of those Crystalieres are doing to get the
feature figures in just the right places on their pots.
But that would defeat the purpose of my trials, which is to get a
glaze with will not flow but has the capacity to develop Willemite
Crystals. I may be unsuccessful but results so far show that there is
the potential for this to work.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Ivor and Olive Lewis on sun 25 jul 04
Dear Ron Roy,
I have no problem in accepting your comments as absolutely valid.
But the question still hangs unanswered.
"What are the physical or chemical mechanisms which allow aluminium
oxide in a silicate solution to inhibit the development of Willemite
crystals ? ".
As I said earlier, my investigation is leading to a conclusion that
this is not necessarily so, and my reading of Sanders book is
reinforcing this opinion.
A simple experiment people may wish to try in a test tube or small
clear vial is to make a solution of Silver Nitrate and dip a clean
length of copper wire into the solution. Just watch the crystals of
Pure Silver grow. This is a chemical reaction.
So if, as you say "The literature is full of references about alumina
oxide being a crystal inhibitor." who initiated this concept, how was
it explained and when was this done?
Best Regards
Ivor Lewis.
Redhill,
S. Australia.
----- Original Message -----
From: "Ron Roy"
To:
Sent: Saturday, 24 July 2004 3:03
Subject: Re: Inhibition of Crystallisation
> Hi Ivor,
>
> Overloading with certain oxides will produce overall
recrystalization - as
> in oxides of Barium, Calcium, Magnesium, Strontium, Zinc - and
Aluminium.
>
> What I was talking about was the large single crystals. These glazes
are
> well know for sliding off pots - and the reason is the low amount of
> alumina in the glaze which - if there in higher amounts - would
inhibit the
> crystals from forming. These types of crystals grow best in a glaze
with a
> a low viscosity.
>
> The literature is full of references about alumina oxide being a
crystal
> inhibitor.
>
> RR
>
>
> >Dear Ron Roy,
> >In a recent post you said "...and alumina is a crystal inhibitor -
> >which explains why crystal glazes tend to run so much."
> >Perhaps you would explain why this is so.
> >I ask because it seems to contradict the results of a recent test
> >series where I loaded a cone 8 transparent high Soda felspar glaze
> >with Zinc Oxide. When fired and cooled to a holding temperature
> >typical of the system recommended in books about crystal glazes
> >the results were glazes with a profusion of typical but small
> >Willemite crystals. This seems to contradict our popular
understanding
> >of the process. Nor, as might be expected from the way we consider
the
> >fluxing action of Zinc, did the viscosity decrease. These glazes
did
> >not flow freely into the catchers.
> >Best regards,
> >Ivor Lewis.
> >Redhill,
> >S. Australia.
>
> Ron Roy
> RR#4
> 15084 Little Lake Road
> Brighton, Ontario
> Canada
> K0K 1H0
> Phone: 613-475-9544
> Fax: 613-475-3513
>
>
______________________________________________________________________
________
> 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.
Ivor and Olive Lewis on sun 25 jul 04
Dear Jim,
An interesting conversation
I am not into rhetorical. I prefer factual.
I am trying to work with "what is", not with "what can be imagined".
You say << I thought I was implying there may in fact be TOO MUCH Zinc
Oxide in the glaze and/or NOT ENOUGH glass formed to support LARGER
CRYSTAL growth. >> No argument with you there. But there is no Zinc
oxide in the original glaze which I am using for an environment in
which to grow crystals. Recall that the environment for crystal growth
that I create has always produced a clear, high gloss, surface with a
minimum amount of flow when it cools . From this I infer that this
material is a homogeneous solution at its maturity temperature.
Following my comments about Shino you present an involved argument and
conclude <<. In effect, Alumina-solubility is lowered>> . Once you
reduce the ability of Alumina to stay in solution it must precipitate.
If there are elements it can react with then new compounds such as an
Aluminium silicate may form. Or it may remain inactive. in which case
the result might be the growth of Corundum crystals. Has this been
observed?
I still return to my original proposition, which I have put to Ron
Roy. "What are the physical or chemical mechanisms which allow
Aluminium Oxide in a silicate solution to inhibit the development of
Willemite Crystals ? ". I would also like to know who initiated this
concept, how was it explained and when was this done?
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
De Ruyter Jean on sun 25 jul 04
Dear Ivor
I don't understand all this fuss about Al=B2O=B3 .
After all those years of firing crystal glazes I know one thing there is =
a
big
difference between the theory and the reality.
Yes there is a basic principle but the reality is so different.
For ex. I have a very reliable glaze formula for nice big flower crystals=
.
I had to change the wiring of my kiln, result farewell the crystals ,I ha=
d
to adapt
the firing cycles.
This example to take just a little part of the facts that influence the
formation of the crystals.
On my site You may see strange crystal formations Gallery 1 1&3 row 2 a=
nd
1 row5
Gal2 1 row 1
This crystals came out of the same kiln after that the firing sickle was
interrupted in de
heating faze, as it was impossible to determine at what temp the
interruption occurred
I could never reproduce that effect even that the glaze formula was the
same.
This is on of many experience.
I have a lot of respect for the job that Fa is doing by registration of a=
ll
her experiences on the net .
But I am sure of one thing crystal glazing
is one of the most difficult, depressing and intoxicating glazing techniq=
ue
that I know.
All the best
Jan
----- Original Message -----
From: "Ivor and Olive Lewis"
To:
Sent: Friday, July 23, 2004 6:27 AM
Subject: Re: Inhibition of Crystallisation
Dear Jean De Ruyter,
Not only that, the form in which the alumina is incorporated into the
recipe has an influence.
The major proportion of Al2O3 in this base glaze is as a felspar
mixture together with a small proportion of Kaolin. But the glaze is a
reliable cone 8 transparent high gloss glaze and individual Zinc
Silicate crystals grow to over five mm diameter.
In Studio Ceramic Technology there is a tendency to use generalised
statements as valid facts. However, when these statements are tested,
they are found to have at least some degree of uncertainty or to be
invalid.
Thanks for your input.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
----- Original Message -----
From: "De Ruyter Jean"
To:
Sent: Friday, 23 July 2004 12:31
Subject: Re: Inhibition of Crystallisation
Ivor
Keep in mind that the max. temperature is of a great importance in
relation
with the
Al=B2O=B3.
If You want to see some results have a look at www.
crystallineglazes.be
If I can be of any help Jderuyter@pondora.be
Jan
----- Original Message -----
From: "John Britt"
To:
Sent: Thursday, July 22, 2004 1:33 PM
Subject: Re: Inhibition of Crystallisation
> Ivor,
>
> Try leaving the alumina out of the glaze and test that. You will
probably
> see much larger crystals,
>
> John
>
>
______________________________________________________________________
______
__
> 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.
>
>
______________________________________________________________________
________
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.
_________________________________________________________________________=
___
__
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.
Fara Shimbo on sun 25 jul 04
Hi, Ivor and Ellie and Ron Roy and all,
If I may be permitted to jump into this conversation...
As to why alumina is considered a crystal inhibitor, to the
best of my knowledge it is this:
In order for the crystals to grow in the first place, zinc
silicate molecules that grow in the glaze must be able to
move in order to find seeds or existing crystals to which to
attach themselves. It is felt -- but in all the research
I've done it has yet to be empirically demonstrated -- that
what with alumina's ability to raise the viscosity of a
glaze, the zinc silicate molecules are limited in their ability
to move about in the melt and find each other. Therefore,
it is felt, by limiting the amount of alumina, one keeps the
fluidity up and thus encourages larger crystals.
I'm not certain I buy this argument for three reasons.
- Firstly, I have added up to 10% alumina to my base glazes and
seen no effect on either the runniness of the glaze or the
size of the crystals (although there has been a profound dulling
effect on colors, particularly copper blues).
- Secondly, I use a couple of raw glazes made with both Kona
and Custer feldspars which crystallize very nicely.
- Thirdly, I have some pots from China that show absolutely no
movement of the glaze on the piece but have nice large crystals.
I don't know the formulation of the glaze, alas.
So I guess I'll have to experiment with this, and find out just how
much alumina/feldspar one can put in a glaze without changing
the pattern of crystal growth. Once the stuidio is finally built,
which will happen after we finally finish fighting with the
[shocking bad words] county building department, but I digress...
As to the matter of growing single, huge crystals, here are some
things to keep in mind.
According to Kingery et al., the critical nucleation temperature
(that is, the temperature at which zinc silicate seeds form in a
crystalline glaze) is about 875 C. At this point, literally
thousands of seeds will form spontaneously, so many that if you
stop the fire at this point, you will get a really ugly matte
surface. As one carries on raising the temperature, these seends
dissolve again, until only a few remain. So in essence you're not
firing higher to mature the glaze, but firing up to the point where
a specific formulation will give you only the number of seeds you
want. It follows, therefore, that if you want only one or two seeds,
either fire higher, hold at peak temperature for a while, OR,
and this is probably the best way to go, put a seed of hemimorphite,
zincite or sphalerite into the leather hard pot at the point you
want the center of your big crystal, and fire to a FULL cone ten.
I have to admit, I've never actually done this. I suppose I should
for the sake of completeness, but I haven't done it yet because I
just don't like the look of a single crystal. Then again I just put
new elements in the test kiln so... hmmm...
On the matter of titanium. It has been my experience with my own
glazes that titanium inhibits zinc silicate crystal growth when there
is more than 9% of it in the glaze; but over 15% you will get both
zinc silicate AND rutile crystals. What titanium seems to do is
opacify both the crystals and the ground. In copper and some iron
colors in some of my glazes (particularly those high in lithium)
the crystals, without titanium, are huge but so transparent they
can hardly be seen. 4 or 5% titanium, or some addition of rutile
or ilmenite, will correct this although it will, of course, change
the color.
Oh well, enough rambling for one day, hang in there, everyone,
Fa
--
=============================================================
Fara Shimbo, Master Crystalliere, Certified Public Nuisance
-------------------------------------------------------------
Shimbo Pottery, PO Box 41, Hygiene, CO 80533 USA 720.207.5201
Crystalline-Ceramics.Info ShimboPottery.com Crystallieri.Org
Klysadel.Net TuranianHorse.Org
=============================================================
Jim Murphy on mon 26 jul 04
Hi Ivor,
Say, while we're awaiting a more specific text reference to "physical or
chemical mechanisms which allow Aluminium Oxide in a silicate solution to
inhibit the development of Willemite Crystals", I thought I'd include the
following bits of info which may or may not add further insight to your
quest:
The "Study Results" section in the following online quasi-related ACerS
Ceramic Bulletin entitled "Soft Porcelain Glazes":
indicates "ZnO produces its own phases in soft porcelain crystalline glazes.
Willemite (zinc silicate, Zn2SiO4) and gahnite (zinc aluminate, ZnAl2O4) are
produced in the presence of a sufficient amount of Al2O3 and SiO2. Even in
the absence of TiO2, which produces nuclei for the development of zinc-based
crystals, ZnO is capable of forming its own crystals." [Ivor, I know you
made no mention of observed gahnite in your test series, however, perhaps
the Article's reference to competing Willemite & Gahnite phases may have
some bearing or may joggle someone else's mind to other applicable text
references.]
Additionally, from the book "Glass-Ceramic Technology" by Wolfram Holand &
George Beall - "A glass-ceramic may be highly crystalline or may contain
substantial residual glass. It is composed of one or more glassy and
crystalline phases. The glass-ceramic is produced from a base glass by
controlled crystallization. The new crystals produced in this way grow
directly in the glass phase, and at the same time slowly change the
composition of the remaining glass." [Ivor, arguably some may say a Zinc
Crystalline Glaze is NOT a glass-ceramic material, but, IF a similar
mechanism is somehow employed, I wonder to what extent the growing Zinc
Silicate crystals are "changing" the "remaining glass composition" (perhaps
the "homogeneous solution" is compromised ?) when a Cone 8 glaze, which
normally fires to a transparent glossy finish, is doped by Zn.]
Hope these references help.
Best wishes,
Jim Murphy
Ivor and Olive Lewis on mon 26 jul 04
Dear Fara Shimbo,
Thank you for joining this discussion.
The points you have put on the table suggest something far more
complex than has so far been imagined.
I will need a fair amount of time to delve into the questions which
arise. If it can be agreed that we are dealing with a true solution,
then we have to forget about the compounds we are dealing with as
being molecular oxides and start to think about them in terms of Ions
in motion in a silicate melt.
There must be a low temperature chemical reaction taking place in our
fluid phase glaze between Zinc ions, Silicate ions and Oxygen ions.
The compound which forms must remain stable in the solution. From
there I find myself in need of a good read and a long think.
One of the things which I find worrisome is that what has been written
about the inclusion or avoidance of Alumina in a recipe is being
treated as true, cast iron, set in concrete and I am an idiot for
doubting the words of those illustrious authors.
So my questions still hang. Who first said it and when?, What evidence
did they use and has this been validated?
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Ivor and Olive Lewis on wed 28 jul 04
Hello again Jim,
Thanks for doing Homework on this one.
Yes, I have been aware of the potential to create Zinc Aluminate for a
long time. It is easy to get to that information when you have access
to Equilibrium Phase Diagrams. Unfortunately my mineral book has no
reference to Gahnite which is I believe, a Spinel. Willemite and
Gahnite belong to differing crystal systems. So it should be possible
to identify which is present in macro specimens.
.
The question of which of these compounds will form first is dependent
on many factors. To name but a few, there would be : The molecular
mass ratios of the ingredients used in the batch; The thermodynamic
conditions employed; The degree of solubility of ingredients in the
original recipe; The range of Substances in the original batch recipe;
The reactivity of Aluminate Ions with species other than Zinc;
Physical characteristics of competing species; Proximity of a
composition to a Eutectic Mixture.
It would be interesting to know if the ACS have Phase diagrams
covering the composition range of popular Crystal glaze recipes. A
search for "Na2O-Al2O3-SiO2-ZnO-B2O3" or the "K2O-Al2O3-SiO2-ZnO-B2O3"
diagrams might yield more knowledge. Diagram 758 "ZnO-Al2O3-SiO2" in
Levin, Robins and Mc Murdie, does shed some light on the problem.
Thanks for this input.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
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