Don Goodrich on thu 1 feb 07
Hi Chris,
Perhaps there's another approach that could do away with the
crazing yet preserve the beauty of the crystals. Have you looked
into other clay bodies? If your suppliers have a variety of
clays that will work with your glazes, it might be worth testing
a few. You might also calculate the expansion coefficient of your
crystalline glazes, then shop around to see if any available
clays have expansion close to that.
Good luck,
Don Goodrich
Chris Groat on thu 1 feb 07
I'm sure there are a million posts on here about crazing and how to
eliminate it. I've been trying to eliminate the crazing from a crystalline
glaze, and the only way I've been able to do it is to sacrifice the beauty
of the crystals. After some research I've decided that it's ok to have
some crazing on a pot, even if it's dinnerware! Here is a quote from the
Potter's Dictionary:
"On earthenware, the glaze is intended to be an impervious layer to cover
an absorbent body. If the glaze crazes, it no longer fulfills this
function function. Crazed earthenware which has been in use for a number
of years will have absorbed dirt with the moisture so that the craze lines
show distinctly. On tableware this is unpleasant and probably unhygienic.
On true stoneware the crazing does not present such a hazard. The body
itself is impoervious and the glaze's function is to present a smooth
hygienic and decorative surface."
I take this to mean that as long as the clay is fully vitrified
(stoneware), a crackle glaze is ok for food. I've been using crackle glaze
myself for years on pots that I made in highschool. Since I setup my own
studio, I've stayed away from them. Perhaps the stigma originated from
earthenware pottery, and has been improperly placed on stoneware?
Any thoughts? I know many will disagree, but I know a few who agree...
Mayssan Shora Farra on thu 1 feb 07
If it is a crackle glaze it is good. If crazed then it's bad. LOL
Mayssan
http://www.clayvillepottery.com
Lee Love on fri 2 feb 07
I am getting some wonderful crazing on one of my new shinos. It is
also showing through iron decoration from beneath, metallic. Also,
on a recalculation of crackle slip and MacKenzie's grey (doesn't look
anything like the original."
Will put up photos soon.
--
Lee in Mashiko, Japan
Minneapolis, Minnesota USA
http://potters.blogspot.com/
"Let the beauty we love be what we do." - Rumi
"When we all do better. We ALL do better." -Paul Wellstone
Lee Love on fri 2 feb 07
I put photos here:
http://claycraft.blogspot.com/
See sushi platter at work too, Scroll down.
--
Lee in Mashiko, Japan
Minneapolis, Minnesota USA
http://potters.blogspot.com/
"Let the beauty we love be what we do." - Rumi
"When we all do better. We ALL do better." -Paul Wellstone
Snail Scott on fri 2 feb 07
At 07:42 PM 2/1/2007 -0500, you wrote:
>I take this to mean that as long as the clay is fully vitrified
>(stoneware), a crackle glaze is ok for food...
>Any thoughts? I know many will disagree, but I know a few who agree...
Actually, this comes up a lot on this
list, and I think many of us do agree.
Bacteria probaby can lurk in the cracks,
but not enough to worry most of us. At
least the earthenware-specific problems
are not a factor: moisture absorption
causing more crazing and bacterial growth,
and the nasty one (in my experience):
oils soaking in, going rancid and stinky.
If you really like the crackle, that's one
thing, but don't cop out if you'd really
rather get rid of it. Tackle the problem
of incompatible CoE for the other side:
the clay. Instead of trying to modify
your glaze, why not try a clay body with
a more compatible coefficient of expansion?
-Snail
Ron Roy on sat 3 feb 07
Hi Chris,
I'm not so sure crazing is a health problem - the small amount of bacteria
in crazing may be just the thing to keep our immune systems strong - but I
would not recommend storing food on such ware - thats just asking for
trouble.
Crazed ware is weak compared to uncrazed ware - the glaze, when it cracks,
cracks the clay a bit - so the ware is less likely to survive a bump or a
drop. If clay has a micro crack it is much more likely to crack.
I think you may also find that crystalline glazes are not stable - either
to acid attack or alkaline attack - in the dish washer. Easy to find out if
your glazes are - have then tested in a lab.
First test - to find grossly unstable glazes is to leave a slice of lemon
on it over night - at room temperature - if you see any change in the glaze
surface or a shadow of the lemon slice you have a very unstable glaze that
will leach all it's components into acidic food.
Leaving a glazed tile in the dishwasher and comparing it to one not in the
dishwasher - every week will tell you how stable it is to alkaline attack.
RR
>I'm sure there are a million posts on here about crazing and how to
>eliminate it. I've been trying to eliminate the crazing from a crystalline
>glaze, and the only way I've been able to do it is to sacrifice the beauty
>of the crystals. After some research I've decided that it's ok to have
>some crazing on a pot, even if it's dinnerware! Here is a quote from the
>Potter's Dictionary:
>
>"On earthenware, the glaze is intended to be an impervious layer to cover
>an absorbent body. If the glaze crazes, it no longer fulfills this
>function function. Crazed earthenware which has been in use for a number
>of years will have absorbed dirt with the moisture so that the craze lines
>show distinctly. On tableware this is unpleasant and probably unhygienic.
>On true stoneware the crazing does not present such a hazard. The body
>itself is impoervious and the glaze's function is to present a smooth
>hygienic and decorative surface."
>
>I take this to mean that as long as the clay is fully vitrified
>(stoneware), a crackle glaze is ok for food. I've been using crackle glaze
>myself for years on pots that I made in highschool. Since I setup my own
>studio, I've stayed away from them. Perhaps the stigma originated from
>earthenware pottery, and has been improperly placed on stoneware?
>
>Any thoughts? I know many will disagree, but I know a few who agree...
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Chris Groat on sat 3 feb 07
I haven't tried the lemon test or the dishwasher test. I did do the
vinegar test as described in MC6G. I'm workin with several different
bases. On all of them, the background glaze was unaffected by the vinegar;
however some color was leached out of the crystals on most of the test
pieces. It's probably not too much of a surprise that the most successful
glazes were the ones where I decreased the level of Na, and increased the
levels of Mg and Ca, and maintained a constant amount of Si and Zn. Also,
the green glazes seemed to leach a bit more than the blue ones. Maybe it's
true that Cu is hard to keep in some glazes? The glazes that I modified by
adding Mg and Ca are also more aesthetically pleasing because they have
opaque backgrounds and provide interesting contrasts between the crystals
and background glaze.
The next step is to find a color that I really like, send it off to lab,
and keep my fingers crossed. My deadline is approaching, so this will be
done within the next three weeks. If the glaze ends up being stable I'll
post the formula, pics, and test results.
I've gotta get back to watching this Chapel Hill game. I can't believe
they're losing to state.... and they play Duke in four days!
Chris
Lois Ruben Aronow on sat 3 feb 07
I happen to like crazing, but not on my own work. I own a lovely set of
commercial dinnerware from France that is crazed and I won't give it up. I
adore it. I do have a few questions however.
I have a question: delayed crazing. On every friggin' mug I have, the
insides eventually craze. (Ironically, hasn't appeared to happen yet on my
own work). I assume it is from heating and cooling in the dishwasher and/or
microwave. I know this is typical of majolica, but was surprised to see it
on porcelain. I don't know what my question really is, as I am pretty sure
that this is how it occurs. I'm not angry that it happens, but sometimes
it's disappointing. Yet another excuse to fill that damn cup full of
coffee....
Note: I don't experience this in my own work, which I do micro and d/w day
after day for years. I don't think I have any magic formula. I'm assuming
it's a combo of my glaze, clay body, unusual bisque schedule, and fit
between my beading and my glossy glazes.
...Lo
***
Lois Ruben Aronow Ceramics
232 Third Street - # B202A
Brooklyn, NY 11215
p: 917..561..2854
f: 718..246.0819
www.loisaronow.com
www.craftsofthedamned.blogspot.com
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Chris Groat
Sent: Thursday, February 01, 2007 7:42 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Crazing! Beating a dead horse...
I'm sure there are a million posts on here about crazing and how to
eliminate it. I've been trying to eliminate the crazing from a crystalline
glaze, and the only way I've been able to do it is to sacrifice the beauty
of the crystals. After some research I've decided that it's ok to have some
crazing on a pot, even if it's dinnerware! Here is a quote from the Potter's
Dictionary:
"On earthenware, the glaze is intended to be an impervious layer to cover an
absorbent body. If the glaze crazes, it no longer fulfills this function
function. Crazed earthenware which has been in use for a number of years
will have absorbed dirt with the moisture so that the craze lines show
distinctly. On tableware this is unpleasant and probably unhygienic.
On true stoneware the crazing does not present such a hazard. The body
itself is impoervious and the glaze's function is to present a smooth
hygienic and decorative surface."
I take this to mean that as long as the clay is fully vitrified (stoneware),
a crackle glaze is ok for food. I've been using crackle glaze myself for
years on pots that I made in highschool. Since I setup my own studio, I've
stayed away from them. Perhaps the stigma originated from earthenware
pottery, and has been improperly placed on stoneware?
Any thoughts? I know many will disagree, but I know a few who agree...
____________________________________________________________________________
__
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You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
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melpots@pclink.com.
Chris Groat on sat 3 feb 07
Yeah, the crazing on the inside of mugs has got to be from the repeated
heating and cooling. In fact, in MC6G a procedure is described for testing
a new glaze to see if it will craze. The procedure basically consists of
heating and cooling the piece, and if it passes the test there's a good
chance that it will never craze. I use a black liner glaze on all my mugs.
If it crazed I probably wouldn't be able to tell, but really I think a
very good liner glaze should be used on anything that you drink out of. At
least your own pottery doesn't have any problems. Wish I could say the
same...
Lee Love on sat 3 feb 07
On 2/2/07, Snail Scott wrote:
> If you really like the crackle, that's one
> thing, but don't cop out if you'd really
> rather get rid of it.
And keep your mind open. It is tough when something doesn't come
out the way you want, but if you put it away for a while, when you go
back to it without any precoceptions, you can see things with a new
eye.
The bottle I posted here: http://claycraft.blogspot.com/
I was about to throw it into the shard bin and Jean stopped
me. An important regular customer at Gallery Shunn bought it. Has
a liner glaze so the crazing on the outside is not problematic.
--
Lee in Mashiko, Japan
Minneapolis, Minnesota USA
http://potters.blogspot.com/
"Let the beauty we love be what we do." - Rumi
"When we all do better. We ALL do better." -Paul Wellstone
Ron Roy on thu 8 feb 07
Hi Eleanor,
Those lines indicate to me that it is the opposite of crazing - shivering.
Also - glaze that is applies thinner is influenced by the clay - I am
assuming that the glaze is thicker in the bottom of the mug.
Crazing always make a pot weaker.
All the high calcium glazes in our book have a low expansion - they would
be the last to craze. If you look at the expansion numbers for the glazes
in out book you can actually use those glazes to teat clay expansion - the
fit testing glazes in chapter 5 are better of course.
RR
>1. My son drinks his tea from my mugs. He pours boiling water (I
>don't know the exact temperature of the water -- he lives at 5000
>feet altitude) into a room-temperature mug. The bottom of the mug is
>crazed in long circular lines resembling the outer edges of a spider
>web. The sides are uncrazed. He has no dishwasher, no microwave (poor
>kid!) and washes by hand in warm water.
>
>2. I preheat my cappuccino mug with water from an instant hot water
>device on my kitchen sink. I believe the water temperature is below
>boiling. The place where the water hits is crazed with a fine-mesh
>pattern. The mug gets another dose of heat when the coffee comes in
>but that is at a much lower temperature. The sides are also uncrazed,
>at least as far as I can see. I hand-wash this mug.
>
>3. I make hot chocolate for my husband in a mug he particularly
>likes. The cold mixture is heated in the microwave and the empty mug
>goes into the dishwasher. The liner in this mug is crazed all over
>with a fine-mesh pattern that is barely noticeable.
>
>I read in Hamer&Hamer and on Clayart that crazing at stoneware
>temperatures is not particularly critical in terms of health but may
>affect the strength of the ware.
>
>I am glazing the mugs I offer for sale with colored glaze so as not
>to alarm the customers but I really like the look of the liner.
>
>My clay is Tucker's ^6 white with and without grog. I fire electric
>oxidation to ^6.
>
>There was discussion recently about the effect of colorants on
>crazing. As liner glazes have no colorants, might there be a connection?
>
>And why does there seem to be two distinct crazing patterns?
>
>Note: M^6G Bone seems to be resistant to crazing. It might make a
>good liner. So far, my bowls have survived the dishwasher but I
>haven't tried mugs yet.
>
>Eleanor Kohler
>Centerport, NY
>
>Ever appreciative of the Clayart gurus!
>
>______________________________________________________________________________
>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.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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