Judith Musicant on thu 4 jun 98
Does anybody else have problems with their cone 6 pots sweating
excessively? My pots are all glazed inside, some with shiny glazes, some
with matte. Most of them sweat when filled with water, some more, some
less. Some vases have sweat so badly that I can't sell them. These pots
don't have any cracks in the bottom--they're not leaking, just sweating. I
have changed my clay body from Standard 182 which fires to cone 8, to a
new Highwater body which is formulated to cone 6. The sweating has gotten
a little better, but has not disappeared. Could it be a problem with my
bisque temp? I've been bisquing to cone 08, (which many of you claim is
too low, but I've not seemed to have any glazing problems as a result).
Any suggestions?
Judy Musicant
Laura Conley on fri 5 jun 98
You mention that there are no cracks, but is there any crazing?
Laura Conley
Boulder, CO
Judith Musicant wrote:
> ----------------------------Original message----------------------------
>
> Does anybody else have problems with their cone 6 pots sweating
> excessively? My pots are all glazed inside, some with shiny glazes, some
> with matte. Most of them sweat when filled with water, some more, some
> less. Some vases have sweat so badly that I can't sell them. These pots
> don't have any cracks in the bottom--they're not leaking, just sweating. I
> have changed my clay body from Standard 182 which fires to cone 8, to a
> new Highwater body which is formulated to cone 6. The sweating has gotten
> a little better, but has not disappeared. Could it be a problem with my
> bisque temp? I've been bisquing to cone 08, (which many of you claim is
> too low, but I've not seemed to have any glazing problems as a result).
> Any suggestions?
>
> Judy Musicant
John Baymore on sun 7 jun 98
------------------
(clip)
Does anybody else have problems with their cone 6 pots sweating
excessively? My pots are all glazed inside, some with shiny glazes, some
with matte. Most of them sweat when filled with water, some more, some
less. Some vases have sweat so badly that I can't sell them. These pots
don't have any cracks in the bottom--they're not leaking, just sweating.
(snip)
A few thoughts here to help out...............
Sweating is leaking. Just more slowly. =3Cwg=3E
This is a two part problem...... your glaze and your clay are in cahoots
against you. Disrupt the partnership. and you solve the problem. Better
yet .... get rid of both of them.
The first culprit is probably the fit between your glaze and your claybody.
My bet is that is is crazed. The cracks might not be obvious to the eye
because of the surface of the glaze and the color..... but it probably is
crazed even if you can't see it easily. If the glaze is not de-vitrifying
(has a suggary grain texture), it isn't crazed, and it fully covers all
the clay on the inside, then it can't leak water molecules through it
(kerosene is another story....as those who make oil lamps know =3Cwg=3E).
The matt glazes may be in actuality =22immature=22 glazes. (Fire them a =
little
hotter and they glass over and become shiny). Which means that they are
not fully melted into glass. If they are this type, they might leak
because that are full of microscopic =22holes=22.
Get a magnifying loupe or one of those hand held lighted microscope pens
that Radio Shack sells. Look closely at the glaze surface from a slight
angle. You'll probably see the craze lines.
If that doesn't show up crazing........ Mix up a very strong solution of
water and india ink. Put it in your pot. Let sit til it sweats pretty
badly. Dump out the solution. Scrub the inside of the pot woth soap and
water (and maybe a Brillo pad). Look at the glaze. Probably see the craze
lines nicely now.
The basic seat of the pants remedy for crazing of a glaze is to increase
the flint content of the glaze (raises the (low CTE) SiO2 ratio in the
fired glass) in small increments until the crazing stops. This might or
might not stop it. The fluxes present in the glaze might be as much of a
culprit, and also need adjusting.
If you have the ceramic chemistry knowledge..... you can check the
molecular formula and readjust the composition of the glaze to correct the
crazing instead of using the empirical =22add flint=22 method. This can
certaily be done by hand with a calculator (or god forbid..... a slide rule
=3Cg=3E), but is is easiest with glaze calc software.
What are the glaze formulas?
The second half of the duo is the clay body. Once the water gets through
the glaze layer (via the craze lines or the microscopic holes) is ALSO
getting through the body. Which means that the body is NOT non-porous. At
your cone range, it certainly is possible to have a very non-porous
body.... so you might look at your clay formulation.
What are the porosity specs from the supplier for the clay? Is it supposed
to be vitrious? It may not be designed to be non-porous at that cone range
at all, and is within the manufacturers specs. Some clays have a wide
=22range=22 that they are sold to be =22acceptably=22 used in (ie. cone 6-10
stoneware). The lower end of the cone range usually has the highest
porosity. Often objectionably so. Add a crazed glaze, and you have
problems.
If that is the case, change to a body that is as tight (non-porous) as
possible at the cone you fire to. Low porosities are possible at that
range. Check around for other clays more specific to that cone range, and
not =22broad range=22. Maybe something like a cone 4-6 clay body....that =
you
are firing on the HIGH end of the range.... not the low end.
What is your firing cycle? Is it =22fast=22? Maybe try slowing down your
firing cycle a bit and let the body develop more glassy phase and
crystaline structures and let the glaze =22fine out=22 a bit and see if the
problem gets better or worse. The body might get tighter and the glaze may
fit better if all of the chemical reactions go more fully to completion.
Sometimes this simple change can improve things greatly, if you have been
pushing the firing time a lot.
This slower cycle can also increase the crazing factor of the glaze. If
you fix that for the fast cycle and then change, it can come back. Watch
for that. That may require more adjustments to the glaze.
The improvement from the first clay body to the second may have been a
better fit between glaze and clay, a lower porisity rating of the clay, or
a combination of both factors. Were you firing the cone 8 body to only
cone 6?
Get a non-crazing glaze and a tight body , and the problem will certainly
stop. Get either one by itself, and the problem will also stop.
Best,
.......................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752
JBaymore=40Compuserve.com
Ardis Bourland on mon 8 jun 98
John's solutions to the sweating problems are certainly good ones and should
be explored. HOWEVER I have yet to see any ceramic pot that didn't leak and
leave wet spots on nice furniture no matter what glaze, clay body or firing
cycle!
Ardis
sweating in Miami
Ron Roy on mon 8 jun 98
I would like to second John Baymore's post on this subject - a well done
and lucid discourse - as usual. And saved me a lot of time as well.
I am surprised this is not a problem voiced here more often. I still see
clay advertized as having a range of 3 or 4 cones. There are not many clays
that are usable over that range without either leakage or slumping - OK I
will say there are no clays that will do the job right over a range of 4 or
5 cones - and I am willing to prove it. The clays I work with everyday -
aside from the earthenware and Raku clays are all recommended for a singe
maturing temperature. If some one has to fire then higher or lower I
eventually talk them into having a custom version made.
>----------------------------Original message----------------------------
>Does anybody else have problems with their cone 6 pots sweating
>excessively? My pots are all glazed inside, some with shiny glazes, some
>with matte. Most of them sweat when filled with water, some more, some
>less. Some vases have sweat so badly that I can't sell them. These pots
>don't have any cracks in the bottom--they're not leaking, just sweating.
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
Cindy on tue 9 jun 98
Ardis,
None of my pots have ever sweated, even when I've had them full of water
for weeks. The exception, of course, is a cold glass of tea on a hot day,
but that doesn't count, methinks.
Cindy Strnad
Earthen Vessels
Custer, SD
USA http://blackhills-info.com/a/cindys/menu.htm
I have yet to see any ceramic pot that didn't leak and
> leave wet spots on nice furniture no matter what glaze, clay body or
firing
> cycle!
> Ardis
> sweating in Miami
Ron Roy on tue 9 jun 98
Well I guess I will join the chorus on this one - I have many hand made
stoneware pots that don't leak - This is not difficult - either get your
supplier to sell you clay that vitrifies at your temperature or find
another who does.
It is a simple mater to test clay for absorption and we should all do it on
a regular basis.
>----------------------------Original message----------------------------
>John's solutions to the sweating problems are certainly good ones and should
>be explored. HOWEVER I have yet to see any ceramic pot that didn't leak and
>leave wet spots on nice furniture no matter what glaze, clay body or firing
>cycle!
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
John K. Dellow on tue 9 jun 98
Ardis Bourland wrote:
> ----------------------------Original message----------------------------
> John's solutions to the sweating problems are certainly good ones and should
> be explored. HOWEVER I have yet to see any ceramic pot that didn't leak and
> leave wet spots on nice furniture no matter what glaze, clay body or firing
> cycle!
> Ardis
> sweating in Miami
Ardis don't confuse the sweating with the potential of a cold pot to condense
moisture, from the atmosphere, on the surface a pot is resting. Especially in ho
& humid weather.
Stephen Mills on tue 9 jun 98
What all this boils down to, is that if for whatever reason people
decide they need to fire at ^6 they have to be sure their glazes are a
perfect fit (nearly impossible given the inevitable variation in
material supply quality), or not make containers (food or otherwise), or
seal, the insides by other means! Or (perish the thought) raise the
melting point of their glazes and fire to vitrification point!
Steve
Bath
UK
In message , Ardis Bourland writes
>----------------------------Original message----------------------------
>John's solutions to the sweating problems are certainly good ones and should
>be explored. HOWEVER I have yet to see any ceramic pot that didn't leak and
>leave wet spots on nice furniture no matter what glaze, clay body or firing
>cycle!
>Ardis
>sweating in Miami
>
--
Steve Mills
Bath
UK
home e-mail: stevemills@mudslinger.demon.co.uk
work e-mail: stevemills@bathpotters.demon.co.uk
own website: http://www.mudslinger.demon.co.uk
BPS website: http://www.bathpotters.demon.co.uk
Stairs interlog on wed 10 jun 98
At 09:37 AM 6/8/98 -0400, Ardis wrote:
>----------------------------Original message----------------------------
>John's solutions to the sweating problems are certainly good ones and should
>be explored. HOWEVER I have yet to see any ceramic pot that didn't leak and
>leave wet spots on nice furniture no matter what glaze, clay body or firing
>cycle!
I wonder about this. I have known many, many tight, leak free clay pots,
glazed and otherwise. However, ANY pot containing a COLD or even COOL
liquid will sweat on a hot, damp day. This is NOT leaking, but
condensation. So the question is, are you sure your pot is leaking, and
not just condensing water from the air? If the latter, there is nothing
wrong with the pot, and there's nothing to do about it: it's just nature's
way.
Gavin
Diane Woloshyn on thu 11 jun 98
Hi Steve,
Are you saying that there is no clay that vitrifies at ^6? Or did I
misunderstand you?
Diane Florida Bird Lady
Judith Musicant on fri 12 jun 98
I've read with interest and appreciation all the thoughtful responses to my
sweating question. Regarding the condensation vs. sweating discussion--I
was not talking about condensation at all. My problem has been strictly
with the bottom of the pot getting damp. In a recent experiment for
instance, I put water in a baking dish (that would obviously not usually be
used for holding water). Dampness began to come through the bottom within
a few minutes, starting as a small circle in the center of the bottom, and
slowly widening out. There was no condensation on the sides. Seems like
a leak of some sort, although not so bad that the wood cradenza it was on
stayed dry. The glaze on this piece happened to be floating blue fired to
cone 6 on Highwater Buncumbe White which is rated for cone 3-6. To your
point, Ron Roy, about clays which should only be formulated for one
temperature, the funny thing is that on another piece made from cone 10
clay at a workshop, and also bisqued there, but glazed and fired at home to
cone 6--no leaking/sweating at all! Makes me think it is a glaze/clay
misfit, or perhaps bisquing at too low a temp. I'll try bisquing at cone
04 and let you know what happens.
By the way, Steve Mills, I too was a little taken aback by your slam of
cone 6. For those of us poor benighted souls doomed to fire in electric
(at least for the time being), cone 6 saves elements and takes
significantly less time to fire--I also achieve some gorgeous glaze
effects, as impossible as that might be to believe. At least my customers
seem to think so.
Judy
Ron Roy on sun 14 jun 98
Hi Judy,
Best way to proceed at this point - glaze fire some ware - with no glaze
and test it for leakage. Better still, fire some clay bars - lets say 6"
long and 1" wide by 1/2 inch thick. Put a line on 10CM long so you can
meaure the wet to dry and fired shrinkage - fire to glaze temp in a normal
firing. Fire them beside a cone - better still make 6 bars and fire them in
different parts of your kiln in groups of 2 - with a cone beside them. Mark
the cone bend right on the bar. While they are still warm from the firing -
don't give them a chance to absorb any atmospheric moisture - weigh em and
mark the weight right on the bar. Boil them for two hours - cool them by
running cold water into the pot, pat them dry and weigh again - right away
before any water has a chance to evaporate, wet weight minus dryweight
divided by dry weight times 100 will give % absorption. If it above 3% you
can expect leaking, or seaping, or sweating - what ever. This is a simple
test as you can do - it is however the test we use when testing all the
clay bodies I work on - we don't get complaints about leakage - whether the
glaze is crazed or not.
I try to keep all our bodies between 2 and 1% - except for porcelain which
I keep closer to none.
Earthenware is hopeless - as is raku - in terms of eliminating leaking and
absorption from sitting in water. The only answer in this case is to have a
perfect glaze that will stop any moisture from moving through it to the
clay - but the ware will always have some water in it from use and washing
which can leave marks on furniture.
The other possibility for sealing clay is using something (like Terra sig)
to seal the clay - I have never done this so I cannot say how effective it
is. My usual recommendation is to move to at least cone 6 where it is
possible to have reliably matured clay.
It is not easy to keep bodies balanced and vitrious - they have to be
watched carefully - testing is mandatory - not only the bodies thenselves
but the raw materials in them - otherwise how would you know when the body
needed to be adjusted. Ask your clay maker to see their test results. If
you are mixing your own - the same kind of testing is necessary - when ever
you get new materials in. And don't assume the raw clay is the same in each
bag. Formulate clays and glazes with as many raw materials as you can -
that way when one varies the consequences are minimized.
I know - some of you are starting to glaze over - was that way myself once
- but this is elementary stuff - if you have data from these simple tests
you will be able to understand what is happening to you - IT'S EASY.
>----------------------------Original message----------------------------
>I've read with interest and appreciation all the thoughtful responses to my
>sweating question. Regarding the condensation vs. sweating discussion--I
>was not talking about condensation at all. My problem has been strictly
>with the bottom of the pot getting damp. In a recent experiment for
>instance, I put water in a baking dish (that would obviously not usually be
>used for holding water). Dampness began to come through the bottom within
>a few minutes, starting as a small circle in the center of the bottom, and
>slowly widening out. There was no condensation on the sides. Seems like
>a leak of some sort, although not so bad that the wood cradenza it was on
>stayed dry. The glaze on this piece happened to be floating blue fired to
>cone 6 on Highwater Buncumbe White which is rated for cone 3-6. To your
>point, Ron Roy, about clays which should only be formulated for one
>temperature, the funny thing is that on another piece made from cone 10
>clay at a workshop, and also bisqued there, but glazed and fired at home to
>cone 6--no leaking/sweating at all! Makes me think it is a glaze/clay
>misfit, or perhaps bisquing at too low a temp. I'll try bisquing at cone
>04 and let you know what happens.
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
Stephen Mills on sun 14 jun 98
Ah, it looks like that I agree, but it's not what I was trying to say.
An awful lot of people do go for lower melting point glazes without
adjusting the body to suit, either through lack of facilities, or lack
of knowledge (that's where the List comes in). Even so there are so-
called cone 6 bodies which frankly are not vitreous at that point, and
glaze fit or sealing ability becomes even more important than before.
Trying to be brief usually means I miss something out!
Steve
In message , Diane Woloshyn writes
>----------------------------Original message----------------------------
>Hi Steve,
>
>Are you saying that there is no clay that vitrifies at ^6? Or did I
>misunderstand you?
>
>Diane Florida Bird Lady
>
--
Steve Mills
Bath
UK
home e-mail: stevemills@mudslinger.demon.co.uk
work e-mail: stevemills@bathpotters.demon.co.uk
own website: http://www.mudslinger.demon.co.uk
BPS website: http://www.bathpotters.demon.co.uk
rudd / jill on mon 15 jun 98
Hi Ron
I have a question about this:
and
absorption from sitting in water. The only answer in this case is to
have a
perfect glaze that will stop any moisture from moving through it to the
clay - but the ware will always have some water in it from use and
washing
which can leave marks on furniture.>
I use earthenware and have had trouble with pots like vases and pitchers
seeping moisture through the bottom. I have found that if I fire to ^03
instead of ^04 most of the problems are eliminated. I still test each
vessel to see if there is seepage. Usually in a kiln-load there will be
5-10% that "leak" and I re-fire them, which is a major hassel. (not the
re-firing particularly, but that in combination with the testing)
My questions:
I haven't done the test that you talk about. Will earthenware always
come out above 3%?
If I leave water in a vase or pitcher for 24 to 48 hours and it doesn't
seep in my studio, can I be fairly certain that the pot won't "leak" for
a customer at some later date?
If earthenware is hopeless, is it pointless to try firing slightly
higher, like ^02? The glaze recipes I use are for ^04. They seem OK at
^03, but I don't know how far I can push them. How would I know whether
I have the "perfect glaze that will stop moisture from moving through to
the clay"?
Boy, if you can answer these questions for me, I will be eternally
grateful!
JILL, in northern Wisconsin where it's hard to know whether summer has
arrived--or not
Tom Buck on tue 16 jun 98
Ron Roy may be giving a course this week so he may not get back to you
immy. His view of lowfire claybodies is essentially correct for most. But
from what you say, your body may come closer to vitification than others.
The usual porosity of EWs is 5-6% but some may get to 3% or lower and then
seepage may cease. A good glaze fit is essential too, it strengths the
pot.
Please recall that a commercial "claybody" contains more than say
a natural clay dug from the riverbank, although if you find such a deposit
that works then you are most blessed. I live on what was once a flood
plain, and there is clay five to six feet down almost everywhere. When I
clean this up and try it as a claybody it is a bit non-plastic but is
throwable. It fires to C04 ok but anymore and it starts to deform. If it
goes to C10 is becomes a rather pleasing darkish brown glossy glaze.
Commercial earthenwares usually are somewhat more tolerant of
over-firing, and they get this way because of other ingredients in the
recipe, always a trade-secret of the supplier.
As for seepage tests, yes, I would expect that if you place say a
vase full of water on paper toweling and see what happens overnight, and
all remains dry, then your pot should be ok for sale. But make sure you
are at room temperature in a slightly humid place (say 50 relative
humidity) because those are the conditions under which it will likely be
used.
As for firing your pots higher, to C03/02, if the body withstands,
the slight rise without warping, then that seems your best shot. But to be
sure, why not do porosity tests and be sure. (See Jan Walker's post of
June 15th). And while you are at it, do some glaze tests too. If the
glazes become too fluid (run too much) they can be adjusted. Til later.
Tom Buck ) tel: 905-389-2339
& snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
(westend Lake Ontario, province of Ontario, Canada).
On Mon, 15 Jun 1998, rudd / jill wrote:
> ----------------------------Original message----------------------------
> Hi Ron
>
> I have a question about this:
>
> > and
> absorption from sitting in water. The only answer in this case is to
> have a
> perfect glaze that will stop any moisture from moving through it to the
> clay - but the ware will always have some water in it from use and
> washing
> which can leave marks on furniture.>
>
> I use earthenware and have had trouble with pots like vases and pitchers
> seeping moisture through the bottom. I have found that if I fire to ^03
> instead of ^04 most of the problems are eliminated. I still test each
> vessel to see if there is seepage. Usually in a kiln-load there will be
> 5-10% that "leak" and I re-fire them, which is a major hassel. (not the
> re-firing particularly, but that in combination with the testing)
>
> My questions:
>
> I haven't done the test that you talk about. Will earthenware always
> come out above 3%?
>
> If I leave water in a vase or pitcher for 24 to 48 hours and it doesn't
> seep in my studio, can I be fairly certain that the pot won't "leak" for
> a customer at some later date?
>
> If earthenware is hopeless, is it pointless to try firing slightly
> higher, like ^02? The glaze recipes I use are for ^04. They seem OK at
> ^03, but I don't know how far I can push them. How would I know whether
> I have the "perfect glaze that will stop moisture from moving through to
> the clay"?
>
> Boy, if you can answer these questions for me, I will be eternally
> grateful!
>
> JILL, in northern Wisconsin where it's hard to know whether summer has
> arrived--or not
>
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