John Baymore on tue 18 jun 96
----------------------------Original message----------------------------
From: Paula Coleman
Subject: crystalline glazes
I have been working with crystalline glazes for a while and getting
radically different results from the interior of the pot to the exterior of
the pot. The inside generally shows the best crystal growth and color,
while the outside is a bit boring. Does anyone know why this happens, and
how I could create beautiful crystals on the outside of the pot as well?
---------------------------------------------------------------------------
Paula,
The interior of a piece trends to retain heat more than the outside of the piece
during cooling. Since crystal development depends on slow cooling at certain
temperatures, the interior may exhibit "better" crystals than the outside if you
are cooling the kiln at a critical point just a little too fast.
To inprove your crystals on the outside, you need to work on two things:
1.) First you need to be able to precisely (in a very literal sense) control
the soaking and cooling rate of the kiln. While this can be done manually with
the aid of a good pyrometer, these days a programmable controller makes the job
much easier.
2.) Second, you need to know the exact points that your particular glaze
formulations "grow" crystals. From this, you will know how to program your
controller for maximum crystal development. While there is a bit of tech info
out there ("Glazes for Special Effects" ....either Sanders or Parmalee......
can't remember right now), a lot of this knowledge comes from empirical testing
of your glazes on your clay bodies.
What you need to do is slow down the firing at the peak to make sure that all of
the materials in the glaze batch are fully involved in the melt (this
"supersaturates" the glass with the stuff the will form the crystals), and then
cool it to the point that the crystal forming stuff percipitates out into
crystals floating on the surface of the glaze. Then you HOLD the temperature
there for as long as you want to get the effect you want. The longer you soak
it at this critical point, the larger the crystals become.
You probably want to look into a controller (or pyrometer, if you go the manual
route) that uses platnium / platnium-rhodium thermocouples rather than the
typical "potter" type that are chromel / alumel. They are much more accurate.
Unfortunatly, they are also much more expensive. If you are working with cone
9-10 crystals, you just about NEED the platnium ones, since the type K (chromel/
alumel) electrical output goes "wacko" in the 2300 and up range, making them
just about useless for accurate work.
I did some consulting for a potter way back in the early 80's who did crystal
glazes. She was doing the kiln control by hand (as was pretty much everyone way
back then ). At that time I was getting into computrerized kiln controls,
and one of the first companies to produce them, Digitree, worked with us to
improve the ability of the controller to hold temperatures without wide
hysteresis (overshoot / undershoot) of temperature. Once we got the controller
software / sensor stuff licked, her crystals were incredible. The current
generation of controllers almost 15 years later should be able to produce
amazing crystals.
Another possibility, however a very, very remote one, is that on the interior,
some material that is in the glaze that is critical to the crystals is not able
to "boil off" out of the glaze as readily as on the outside of the pot (fume is
the technical term). This is making the composition of the inside fired product
different from the outside, even though the glaze batch was the same.
You could look at this sort of like humidity in the air. If the air is "dry"
(not much water vapor in it), water in a bowl evaporates into the air readily.
If the air is humid (lots of water vapor in it), the water in the bowl doesn't
evaporate as quickly. The fumes of metals and metallic earths sort of can act
in the same way.
Now take this analogy to the pot in the kiln. The enclosed space of the
interior (particularly on closed forms) doesn't take much tin (for example) to
raise the "humidity" of tin (tech term is partial pressure) inside that
contained space. The air in the kiln however, will hold much more because there
is a lot more of it. So the tin on the interior of the pot doesn't vaporize out
of the glass as readily on the interior surface as it does on the outside of the
pot. SO......... if the tin is the critical material in the crystal development
in your glaze, then enough of it is still present upon cooling to make good
crystals on the inside, but not on the outside.
(My apologies for seriously oversimplifying this partial pressure concept for
those of you who are highly in tune with this subject .)
My guess is that the issue is on the cooling cycle. Good luck.
..................................john
John Baymore
River Bend Pottery
Wilton, NH
76506.3102@Compuserve.com
http://www.CraftWEB.com/org/jbaymore
John Baymore on thu 20 jun 96
My brain must have been in low gear last night........ . Sniffing too many
fumes coming off of the kiln .
In my reference to "boiling off" (fuming) of materials I was thinking "zinc"
(since the topic was crystal glazes), and my fingers typed "tin". Tin was not
the best choice of examples to use. Zinc is a good example since it readily
departs from the glaze batch given the wrong conditions.
Sorry for any confusion.
.........................john
John Baymore
River Bend Pottery
Wilton, NH
76506.3102@Compuserve.com
http://www.CraftWEB.com/org/jbaymore/rivrbend.shtml
Christine Taylor on fri 18 apr 97
Since NCECA have joined clayart and find messages interesting.
I still like Las Vegas as I won $250 on the quarter one-armed bandit!
I have been experimenting with cone 9 crystalline glazes for quite a number
of years
and have done numerous tri-axials to get interesting colors. The one color
that I
have the greatest trouble with is a black matrix(background). I have tried
about
12 different black stains and many cobalt percentages etc. and have only come
up
with one almost black matrix but it only works on a flat surface and the
stain is no longer available.
Does anyone have any ideas?
Thanks Christine Taylor (its almost 80deg.F here near Los Angeles, so I can't
complain)
Joyce Lee on tue 8 aug 00
Hey Cobus....... I know little about crystalline glazes although they've
intrigued me since I first came on Clayart and Rose Downs from Texas was
the premier crystal glazer ...... however, Brad Sondhal has a website
that includeds crystalline glaze information..... I click on it from
time to time just because it's so lovely ..... think of myself as a
Crystal Glazer Gazer ..... sort of like a crystal groupie...
Brad's url is:
http://www.camasnet.com/~asondahl/crystal.html
Joyce
In the Mojave going out to search for the small desert tortoises ...
hoping they're still around and haven't become raven fodder .... think
I've seen signs of at least a couple lately ...hope it's Toughy who used
to sleep upside down in #1 Support Person's shirt pocket as we watched
football ..... futbol americano, that is.......
Brad Sondahl on wed 9 aug 00
Thanks to Mojave Joyce for mentioning my site, but I have to stress that
it has moved to the address below. Unfortunately I have no experience
with crystalline glazes below cone 10.
--
Brad Sondahl
New Homepage: http://pages.about.com/bsondahl/index.html
New commercial pottery page http://sondahl.safeshopper.com
Original literature, music, pottery, and art
Pettina Hetherington on tue 22 apr 03
Dear Clayart Subscribers,
Below is a query from my brother Dan, who does not have access to the
internet.
thankyou for your help,
Pettina
Hello,
My name is Dan and I have been experimenting with macro crystalline glazes
for about one year. I have been achieving some excellent results but have
come to a hurdle, which I have been unable to get over. I hope that one of
you may be able to help me.
I am firing in a 9 cubic foot electric kiln and have experimented
extensively with one glaze. I have been able to produce a 3 1/2 to 4 1/2
inch crystal. The problem is I can not seem to reduce the amount of seeding
agent to prevent the crystals from clustering all over the pot.
Here are the things I have tried without success, months of hard work and
lost firings:
* Holding at high temps for a period, but when the right amount of seeding
agent melted in, the glass moved off the pot too much
* Crushing all seeding agents and sieving them through fine mesh (around
150)
* Removing and adjusting all seeding agents in the formula
* Increasing the amount of glaze to move them through the glass
* Putting the glaze on thinner so there is not as much seeding agent to
start with
All my crystalline work has been with vases and vertical surfaces. I have
also had problems with the seeding agents sticking on the shoulders and
clustering.
Any help or advice would be much appreciated,
Dan
Fabienne Micheline Cassman on tue 22 apr 03
Greetings,
I don't have THE answer for your brother, but here are my thoughts on the subject:
Normally firing the glaze longer takes care of getting rid of excess crystals, but has Dan mentioned it may run off if held at top temp for too long.
The alternative that comes to mind, although it sounds like it may add up to the same runny result, is to reformulate the glaze such that it melts at a lower temperature and use his usual firing schedule. A simple line blend may be the answer to see if and what works. This may however alter colors particularly if a new flux is introduced.
Perhaps worth a thought, alumina inhibits crystal formation. From a triaxial blend I did, alumina also promoted secondary crystals and altered the color; the amount varoed between .04 and .14 moles in my concoction. I was told that boron (ambiguous bugger) also inhibits crystals, but I haven't used it in excess of what is found in FF3110 which is called for in this type of glazes.
Frank Gaydos has a great page at http://home.earthlink.net/~fgaydos/frits.html where every flavor a frit can be found and don't forget to look at his great slides :)
Fabienne
--
Fabienne Cassman http://www.milkywayceramics.com/
WARNING: I cannot be held responsible for the above
because my cats have apparently learned to type.
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Ellie Blair on tue 22 apr 03
I am having some of the same problems with crystalline. What are you using
for your seeding agent? I work mostly with zinc oxide and silicate glazes. I
have been told that the thickness of application can play a part in how many
crystals you may get. I have been experimenting with this and am having some
success.
Ellie Blair
----- Original Message -----
From: "Pettina Hetherington"
To:
Sent: Tuesday, April 22, 2003 2:29 AM
Subject: Crystal Glazes
> Dear Clayart Subscribers,
>
> Below is a query from my brother Dan, who does not have access to the
> internet.
>
> thankyou for your help,
> Pettina
>
>
>
> Hello,
>
> My name is Dan and I have been experimenting with macro crystalline glazes
> for about one year. I have been achieving some excellent results but have
> come to a hurdle, which I have been unable to get over. I hope that one of
> you may be able to help me.
>
> I am firing in a 9 cubic foot electric kiln and have experimented
> extensively with one glaze. I have been able to produce a 3 1/2 to 4 1/2
> inch crystal. The problem is I can not seem to reduce the amount of
seeding
> agent to prevent the crystals from clustering all over the pot.
>
> Here are the things I have tried without success, months of hard work and
> lost firings:
> * Holding at high temps for a period, but when the right amount of seeding
> agent melted in, the glass moved off the pot too much
> * Crushing all seeding agents and sieving them through fine mesh (around
> 150)
> * Removing and adjusting all seeding agents in the formula
> * Increasing the amount of glaze to move them through the glass
> * Putting the glaze on thinner so there is not as much seeding agent to
> start with
>
> All my crystalline work has been with vases and vertical surfaces. I have
> also had problems with the seeding agents sticking on the shoulders and
> clustering.
>
> Any help or advice would be much appreciated,
> Dan
>
>
____________________________________________________________________________
__
> 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 wed 17 mar 04
Dear Friends,
Another "Back to Basics" idea.
Olive has asked me to create some Zinc Crystal work and I have a lot of =
small narrow bowls thinly thrown in porcelain which would be ideal =
canvases for this style of glaze. Got a new pyrometer I can dedicate to =
the kiln for temperature control. All ready to start weighing and =
brushing.
I have been looking through the recipe base and one thing took my eye. =
Most of the current crop of glazes are based on some form of Frit to =
which is added a proportion of Zinc Oxide and a smaller proportion of =
Silica. I like this idea because it cuts out the liquid Sodium Silicate =
of earlier examples.=20
So the question is, how are these proportions of ZnO and SiO2 =
determined? Do they come about through trial and error? Are they the =
result of applying Ian Currie's Rules? Is there some sort of reasoning =
behind the mummers. If so, what logic is concealed in the numbers?
Please do not send me any recipes unless you are answering these =
questions with examples that illustrate your ideas.
Thanks a lot for any help you can give me with this one.
Best regards,
Ivor Lewis. Redhill, South Australia
Ababi on wed 17 mar 04
Dear Ivor.
I am afraid Ian cannot cure us this time.
The amount of Al2O3 you need in the glaze is minimal and his regular rules
will take you away from the game.
The rules are very simple. Therefore they are so hard.
you need around 50% frit 4110 or similar ( I use a similar with no B2O3 at
all.)
you need 20-25 Calcined zinc
You need 20-25 quartz.
If you fire to ^6 you need 2-5 lithium carbonate.
The alumina I use in ^6 is 0.04-0.05 mol- perhaps higher ha little more.
I have the alumina as calcined red clay, calcined kaolin or spodumen.
I made a recipe using 3110 (4110) for my inter cosmos relations.
I made the test after I could not use again the red clay I had and moved to
another one.
I was a choice to ask myself these questions you are asking in this letter.
I find the quardaxial blend good for this kind of question, at list for your
first investigation.
You can see in this page:
http://members4.clubphoto.com/ababi306910/1310421/
scroll down to the 14th row. the picture in the left and the next ones.
I was too lazy and made only 20 tests. Lawrence has mercy for lazy potters!
Corner A was
Was my regular recipe with 23 zinc 20 quarts and 2 lithium carb
Seger Weight%
KNO 0.325 12.60%
CaO 0.079 2.74%
MgO 0.004 0.11%
ZnO 0.549 27.57%
Li2O 0.043 0.79%
Al2O3 0.049 3.08%
SiO2 1.431 53.11%
K2O 0.008 0.46%
Na2O 0.317 12.14%
B was the same, I increased the frit and reduced the lithium
Seger Weight%
KNO 0.336 12.80%
CaO 0.082 2.79%
MgO 0.004 0.11%
ZnO 0.556 27.41%
Li2O 0.022 0.39%
Al2O3 0.050 3.09%
SiO2 1.467 53.42%
K2O 0.008 0.46%
Na2O 0.328 12.34%
Corner C was 27 zinc and 16 silica
Seger Weight%
KNO 0.297 12.49%
CaO 0.072 2.72%
MgO 0.004 0.11%
ZnO 0.588 32.08%
Li2O 0.039 0.78%
Al2O3 0.045 3.05%
SiO2 1.211 48.77%
K2O 0.007 0.46%
Na2O 0.290 12.03%
And D was 20 zinc and 23 silica
Seger Weight%
KNO 0.350 12.68%
CaO 0.085 2.76%
MgO 0.005 0.11%
ZnO 0.514 24.14%
Li2O 0.046 0.79%
Al2O3 0.053 3.10%
SiO2 1.627 56.42%
K2O 0.009 0.46%
Na2O 0.342 12.22%
If you want to learn more from the glaze wizard do not hesitate to ask!
Yours
Ababi
----- Original Message -----
From: "Ivor and Olive Lewis"
To:
Sent: Wednesday, March 17, 2004 7:57 AM
Subject: Crystal Glazes
Dear Friends,
Another "Back to Basics" idea.
Olive has asked me to create some Zinc Crystal work and I have a lot of
small narrow bowls thinly thrown in porcelain which would be ideal canvases
for this style of glaze. Got a new pyrometer I can dedicate to the kiln for
temperature control. All ready to start weighing and brushing.
I have been looking through the recipe base and one thing took my eye. Most
of the current crop of glazes are based on some form of Frit to which is
added a proportion of Zinc Oxide and a smaller proportion of Silica. I like
this idea because it cuts out the liquid Sodium Silicate of earlier
examples.
So the question is, how are these proportions of ZnO and SiO2 determined? Do
they come about through trial and error? Are they the result of applying Ian
Currie's Rules? Is there some sort of reasoning behind the mummers. If so,
what logic is concealed in the numbers?
Please do not send me any recipes unless you are answering these questions
with examples that illustrate your ideas.
Thanks a lot for any help you can give me with this one.
Best regards,
Ivor Lewis. Redhill, South 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.
Nancy Udell on wed 5 sep 07
Bill Schram posts to the list often.
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
John Thompson on thu 6 sep 07
Thank you everyone for the contact information for Mr. Bill Schran. Thank =
you all for your support.=0A=0A=0A=0A=0A----- Original Message ----=0AFrom:=
Nancy Udell =0ATo: paclayplay@YAHOO.COM=0ACc: claya=
rt clayart =0ASent: Wednesday, September 5, 2007 =
5:16:47 AM=0ASubject: Crystal Glazes=0A=0ABill Schram posts to the list oft=
en. =0A-- William "Bill" Schran=0AFredericksburg, Virginia=0Awschran@cox.n=
et=0Awschran@nvcc.edu=0A=0A=0A =0A___________________________________=
_________________________________________________=0APinpoint customers who =
are looking for what you sell. =0Ahttp://searchmarketing.yahoo.com/
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