David Hendley on wed 13 apr 05
In my own work I work really hard at producing non-crazing glazes
by adjusting glaze formulae on the molecular level.
Still, with my best efforts, I get some crazing as well as some
"delayed crazing" which shows up after months of years of use
(especially on casseroles).
Some of my favorite pieces to use, however, are crazed. I especially
like crazed and stained coffee mugs. I even have a crazed and
stained plate that I like to use. I made it specifically to test a matt
white glaze that was offered on Clayart years ago as a craze-free
high-magnesium matt white. "Ha," I thought, "we'll see," since I
have never found such a glaze that does not craze - and this
one is no exception.
Like many people, we receive tons of gift catalogs in the mail,
and, from time to time, I notice dinnerware for sale in some of
these catalogs that is advertised as "crackle ware". They use
horribly crazed celadon or bottle-glass type glazes, and the
results do look pleasing, even if the idea offends my sensibilities.
A serious and competent potter should have some control
over crazing - factor it in if they want it, or out if they don't.
Functional stoneware potters should also test, and adjust as
necessary, their claybodies, so the body will have low absorption,
a second line of defense against seeping even if the glaze crazes
immediately or later.
David Hendley
I don't know nothin' but the blues, cobalt that is.
david@farmpots.com
http://www.farmpots.com
----- Original Message -----
> So many posts relate to crazing problems. I have many pots, especially
> mugs, by well-known and respected potters, where the liner glaze is
> clearly and profoundly crazed. I have an Ellen Shankin casserole in which
> the liner glaze is obviously crazed. I've been using these pots for
> years, with no obvious detriment to me or the pot. They don't seep and
> they remain fully functional. I can understand that you wouldn't want
> major crazing on a plate, or the inside of a bowl where it would interfere
> with the aesthetics of the piece. Even in those cases, I've seen bowls
> and plates where the glazes appeared to be intentionally crazed. So why
> all the angst about glazes that craze, expecially if the glaze stands up
> to repeated use?
joethepotter1948 on thu 14 apr 05
I grew up not far from a pioneer Tuberculosis rehab hospital, and it
was a firmly held belief back then that cracked cups, despite
regular careful washing, aided in the spread of TB by harbouring
germs from that disease. Additionally, my wife is a microbologist
as well as a world-class cook, and she will not use any food or
drink container that is cracked or crazed, claiming that bacteria
and viruses are insidious little creatures. Me, I just do as I'm
told. Well, at least most of the time. ;)
Joe in MO
--- In clayart@yahoogroups.com, John Hesselberth wrote:
---(snip)
> I am told some county health departments will reject crazed
> dishes in a restaurant. Whether they have data to support doing
that or
> not, I don 't know. But if you plan to sell your work into
commercial
> establishments you may want to check this out more carefully.
---(snip)
> So while I do drink out of crazed
> mugs, I think about it every time I use the mug and wonder why the
> potter didn't fix that.
>
> But, again, it is one of those "you decide" questions. There is no
> universally agreed on position.
>
Louis Katz on thu 14 apr 05
Sooner or later someone will get ill or even die from crazed glazes.
Sooner or later someone will die from living in too clean an
environment as a child and developing horrible allergies. It probably
has already happened. The big move towards controlling bacteria in our
environment has been the last two centuries and has had many positive
effects. I think they outweigh the negatives, but I also think our
attitudes are going to have to change some if we are going to become
even more hardy, healthy, and long lived. Afraid of dirt isn't going to
help us more than it already is.
I am concerned about stuff leaching from glazes but think I have more
to worry about from residues of soaps, shampoos, and other products and
offgassing of pastics in my home, car exhaust, plastic residue in food
etc.
At the same time I think it wise not to store your meatloaf uncooked in
a crazed vessel. Why tempt fate? Since the public cannot be expected to
differentiate between their crazed and uncrazed ware, perhaps the
conservative approach is to not sell crazed ware. In this sense I am
conservative. At the same time Ron Roy got my well pocked teabowl a few
years ago and I am sure he uses it daily:).
Louis
On Apr 13, 2005, at 5:31 PM, Liz Willoughby wrote:
> Judy,
> To tell you the truth, a little bit of crazing on high fired (cone10)
> work does not bother me, because the clay is pretty vitreous at that
> temp, and I just don't think that it is a health concern. I do think
> it is a concern for earthenware or possibly even mid-range work.
> Like you, I have lots of pottery in my kitchen that is crazed. A lot
> of shino in fact. The inside of tea pots quite often get crazed,
> because of their repeated use of pouring boiling water in them, and I
> quite like the pattern from the tea in the crazed lines.
> I think what we have to worry about is not the crazing of glazes, but
> of the leaching of toxic chemicals into our food and drink from
> glazes that are not formulated properly, or that have toxic materials
> in them, i.e. lead, cadmium, on and on. that is unstable glazes.
>
> Meticky Liz from Grafton, Ontario, Canada.
>
> p.s. who is quite fine without any dog, or cat for that matter, and
> prefers it that way. So Joyce, stick with your westie, and forget
> the guard dog. Your westie lets you know doesn't it, when something
> is amiss?
>
>
>> So many posts relate to crazing problems. I have many pots,
>> especially mugs, by well-known and respected potters, where the
>> liner glaze is clearly and profoundly crazed. I have an Ellen
>> Shankin casserole in which the liner glaze is obviously crazed.
>> I've been using these pots for years, with no obvious detriment to
>> me or the pot. They don't seep and they remain fully functional. I
>> can understand that you wouldn't want major crazing on a plate, or
>> the inside of a bowl where it would interfere with the aesthetics of
>> the piece. Even in those cases, I've seen bowls and plates where
>> the glazes appeared to be intentionally crazed. So why all the
>> angst about glazes that craze, expecially if the glaze stands up to
>> repeated use?
>>
>> Best,
>> Judy Musicant
>
> _______________________________________________________________________
> _______
> Send postings to clayart@lsv.ceramics.org
>
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>
Paul Lewing on thu 14 apr 05
on 4/14/05 5:53 AM, joethepotter1948 at joe_cooper@HOTMAIL.COM wrote:
> it
> was a firmly held belief back then that cracked cups, despite
> regular careful washing, aided in the spread of TB by harbouring
> germs from that disease. Additionally, my wife is a microbologist
> as well as a world-class cook, and she will not use any food or
> drink container that is cracked or crazed, claiming that bacteria
> and viruses are insidious little creatures.
This attitude has always mystified me. Why would one assume that there are
germs there that can withstand a dishwasher or a microwave? If there are,
we've all got bigger problems than crazed glazes.
And then the same people who will not use a crazed glaze will eat a salad or
a hamburger off any old plate without a second thought. How many people
have you heard of being killed by germs on lettuce or hamburger, compared to
how many you've heard about being killed by germs from glazes?
And then there are the people who are afraid they'll get sued. I don't get
that either. How could you possibly prove that someone had been infected
that way? You'd have to prove that the germs were down in the crazes. How
could you do that? If the piece had ever been washed or microwaved after
the alleged contamination, you'd have no evidence. And how could anyone
possibly prove that the germs were in the glaze and not on the food?
Sure, lawyers will claim anything to make money, but I can't believe any
lawyer in the world would think he could make that case.
Paul Lewing, Seattle
Janet Kaiser @ The Chapel of Art on thu 14 apr 05
*** IN REPLY TO THE FOLLOWING MAIL:
*** From: Judy Musicant
>snippety-snap
>So why all the angst about glazes that craze, expecially if the glaze=
stands up to repeated use?
*** PREVIOUS MAIL ENDS HERE ***
Not at all, Judy, but some people enjoy wallowing in CP* and lie in bed at=
night dreaming of the zillions of germs swarming out of the cracks and=
amassing on their plates ready to gobble them up... These nightmares=
inform there day-to-day angst-ridden existence... You are about to receive=
a round dozen or so DIRE WARNINGS not to use those crazed items not matter=
how famous the maker.
If you do a little search around the Clay Town archives, you will see who=
the posters are likely to be. Diametrically opposite are others like me=
who only see crazing as a slight imperfection and the inevitable end=
result or rather a symptom of the ageing process.
The only time I personally start to dislike crazing, is when a light=
coloured body/background starts to discolour in large patches, through=
staining of the body beneath the glaze. That can look perfectly awful and=
unappetizing, especially on plates but unlike the CP brigade, I expect no=
dire consequences.
*CP crazed paranoia
Sincerely
Janet Kaiser -- immersed in books on wood preservation and amazed to see=
our Pitch Pine newel posts are probably a product of the USA!!!
THE CHAPEL OF ART - or - CAPEL CELFYDDYD
8 Marine Crescent : Criccieth : GB-Wales LL52 0EA
Plan visiting The International Potters Path?
Contact: Janet Kaiser
Tel: ++44 (01766) 523122
http://www.the-coa.org.uk
--
No virus found in this outgoing message.
Checked by AVG Anti-Virus.
Version: 7.0.308 / Virus Database: 266.9.8 - Release Date: 13/04/2005
Edouard Bastarache Inc. on thu 14 apr 05
Paul,
good point.
Lee Love once told us that many Japanese happened to live to be
very old even if they ate all their life from crazed ceramic wares.
Experience is a key factor while discussing this issue.
Good hygiene of the wares is naturally very important,
it is also very important when it comes to non-crazed wares.
Later,
"Ils sont fous ces quebecois"
"They are insane these quebekers"
"Están locos estos quebequeses"
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
www.sorel-tracy.qc.ca/~edouardb/Welcome.html
http://perso.wanadoo.fr/smart2000/index.htm
http://www.digitalfire.com/education/toxicity/
Linda Ferzoco on thu 14 apr 05
Paul,
I have news for you. There are germs that can survive live steam under
15-20 psi pressure for 30-60 minutes! This has been shown repeatedly, by
design or accident, in laboratory settings. And interestingly, they can be
especially lively if they're buried under a layer of cooked on protein.
Luckily, and most of the time, those are nasty pathogens that you wouldn't
encounter in your dishware. Also, luckily, we've evolved to deal with the
level of microorganisms in our world, so we don't have to, shouldn't try to,
sterilize our world.
A microbiologist would probably not use a crazed drinking/eating vessel.
Their loss.
Linda
On Thu, 14 Apr 2005 11:08:05 -0800, Paul Lewing
wrote:
>
>This attitude has always mystified me. Why would one assume that there are
>germs there that can withstand a dishwasher or a microwave? If there are,
>we've all got bigger problems than crazed glazes.
Vince Pitelka on fri 15 apr 05
> Zillions of salt/soda fired pots have been used for centuries without
> collective harm to zillions of people.
> For instance, consider the people of Germany were salt firing was
> invented centuries ago.
Thanks Edouard, but that doesn't address my question. In my previous post,
I stated clearly that I do not believe that crazing is a health issue at
all. It is a structural flaw. Thus my question. I still want to know if
anyone has ever tried to combat crazing in salt-fired wares, in order to
make stronger, more resilient wares.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
URL Krueger on fri 15 apr 05
On Thursday 14 April 2005 09:22 am, Lee Love wrote:
>Scientist ... have discovered that the small amounts of
> copper that leaches into the water does in fact kill
> bacteria.
I found an article on the web a while back about a study of
hospital door push plates. They found that by using copper
instead of stainless steel the number of viable bacteria on
the push plate was dramatically reduced. Not many
hospitals were switching though because the copper develops
a patina and people think it is dirty.
Thus proving that perception is more real than reality.
--
Earl K...
Bothell WA, USA
dementedjeffery on fri 15 apr 05
In response to the comment about a microbiologist not liley using a
crazed vessel to eat or drink from, just thought I'd let you know
that a pair of microbiologists I know in San Diego have these crazed
mugs that they use for coffee in their office. we once talked about
the idea that bacteria and other microorganisms can get into glaze
cracks and they more or less laughed at me and pointed out that each
time I go surfing, I probably expose myself to far worse organisms
than live in their coffee mugs.
--- In clayart@yahoogroups.com, Linda Ferzoco wrote:
> Paul,
>
> I have news for you. There are germs that can survive live steam
under
> 15-20 psi pressure for 30-60 minutes! This has been shown
repeatedly, by
> design or accident, in laboratory settings. And interestingly,
they can be
> especially lively if they're buried under a layer of cooked on
protein.
>
> Luckily, and most of the time, those are nasty pathogens that you
wouldn't
> encounter in your dishware. Also, luckily, we've evolved to deal
with the
> level of microorganisms in our world, so we don't have to,
shouldn't try to,
> sterilize our world.
>
> A microbiologist would probably not use a crazed drinking/eating
vessel.
> Their loss.
>
> Linda
>
> On Thu, 14 Apr 2005 11:08:05 -0800, Paul Lewing
> wrote:
> >
> >This attitude has always mystified me. Why would one assume that
there are
> >germs there that can withstand a dishwasher or a microwave? If
there are,
> >we've all got bigger problems than crazed glazes.
>
>
_____________________________________________________________________
_________
> Send postings to clayart@l...
>
> 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@p...
David Hewitt on fri 15 apr 05
I have spent a lot of time over the years on understanding why glazes
craze and how to correct it, but I do not consider it so terrible. It
all depends on what the item is intended to be. For some decorative
items crazing can be a positive advantage. As an example, my tulip range
of decorative bowls and vases, the slight crazing over those areas which
over a copper oxide slip, the crazing gives an added veining effect and
so breaks up an otherwise plainer area.
There is a lot more to ceramics than making functional ware.
--
David Hewitt
Web:- http://www.dhpot.demon.co.uk
Vince Pitelka on fri 15 apr 05
As I have understood it all these years, in midrange and high-fired ware,
crazing is primarily a structural flaw. By examining cross-section cuts of
crazed ware, it has been shown that the craze lines do extend down into the
clay-glaze interface, and thus inevitably will slightly weaken the vessel,
creating "paths" for breakage. A crazed pot simply isn't quite as durable
as an uncrazed one. In ceramic science, crazing is viewed as a flaw, even
though there are plenty of ceramic products that are purposefully produced
with "crackle glazes."
I looked through my files of posts that deal with crazing and toxicity, and
I cannot find one that I distinctly remember. It may well have been saved
on my previous laptop, and at the time I switched over to this one, I didn't
know how to transfer over my mailboxes, and thus lost whatever messages I
had saved. The one I remember was posted quite a few years ago, and it
specifically dealt with crazed ware and issues of toxicity. Could it have
been from Edouard? At any rate, the general point of the message was that
there is absolutely no evidence that bacteria hiding in crazed pottery has
ever sickened or poisoned anyone, regardless of the firing temperature.
Apparently it just doesn't happen, as long as the wares are used with
reasonable standards of hygiene and cleanliness.
I do feel bad for the people who are hyper-paranoid about bacteria and
cleanliness, constantly envisioning vast legions of insidious microorganism
waiting on all surfaces at all times. I mean, they ARE there, but our
immune systems are intended to deal with that situation. Being
super-paranoid about such things is a hard way to go through life, and I
feel especially bad for children who are raised in such an atmosphere,
because they develop a greater susceptibility to bacteria and disease. You
clearly see that happen all over the world. Don't drink the tap water in
Mexico, don't eat fresh vegetables in India. People who live in those
countries don't have a problem drinking the tap water or eating fresh
vegetables. If one of us were to suddenly start serving and storing wet
foods in unglazed clay pots, we would likely experience severe
gastrointestinal distress or worse. From long exposure, people who grow up
in those traditions develop a higher level of resistance to bacteria and
disease.
Unless one is making non-utilitarian products with "crackle glazes" intended
to craze, it makes best sense to try to eliminate crazing, in order to have
stronger, more resilient wares. That is especially true with any sort of
utilitarian wares. People like Ron Roy, John Hesselberth (through their
book "Mastering Cone 6 Glazes") and Jonathan Kaplan have worked very hard to
eliminate crazing in the glazes they use, and openly share advice and
information here on Clayart. Books like Lawrence's "Ceramic Science for
the Potter" and Frank and Janet Hamer's "The Potter's Dictionary of Ceramic
Materials and Techniques" give good advice on dealing with crazing.
I'm interested in the fact that crazing seems so inevitable in salt and soda
firing, but I think I'll address that in another post.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Ben on fri 15 apr 05
Steve S.:
Eduoard B. : be
very old even if they ate all their life from crazed ceramic wares.>
I'm surprised no one has pointed out the fact that the absorption rates
for fired earthen ware are 10 -22%. I think there is a legitimate western
cultural aversion to crazed ware based in the predominance of earthenware
production and a lack common hygeine (i.e running water and sewerage) up
until the 19th c. I think early american stoneware production was not alway
so technical as to ensure vitrified bodys thus the popularity of albany slip
as a liner glaze.
It seems like a stoneware or porcelain body approaching vitrification in the
.5 to 3% range (and I'd rather like under 2%) is a whole 'n'other issue and
a culture based in relating to such wares is bound to have different
experiences and attitudes. There is so much cross cultural communication
these days and so much is lost in translation apart from the cultural
context that they all in danger of being invalidated. Or steadily eroded...
Take care,
Ben
Tim Steele on fri 15 apr 05
Someone, maybe John H., made the point that crazing is, or can be, a choice.
Even on functional ware. Crackle galzes. I used to make cone 10 vases
using a Rhodes glaze, Number 20, composed of Cornwall Stone and whiting.
When I removed them from the firing, they "pinged" for several hours. I
called them singing vases. Following Rhodes' sugestions I would rub India
ink on them to excentuate the crazing. It seems to me that these types of
uses of crazing fall within the concept of good craftmenship: Knowing the
properties of your tools and materials and using them effectively to
achieve a desired and planned end.
I always warned people that these vases were not food safe. Basically
repeating the stories of my youth without knowing their veracity. Although
it made me laugh to think of someone using a bud vase for food. Their
design hardly suggestged that usage.
Tim Steele
www.steelepots.com
Lee Love on fri 15 apr 05
I prefer crazed glazes in the green tea bowls I use.
Tea is an antiseptic* and the crazing helps keep tea in the cup. This
is good, just in case some bad bacteria tries to jump into my tea cup. ;-)
*At zen monasteries, you clean your eating bowls at your
sitting place. The final wash is with green tea and you drink the wash
water (there is a chant about the washwater tasting like ambrosia!)
The antiseptic nature of green tea helps keep the bad stuff from growing
in your lacquer bowls.
I also heard about a study in India a couple days ago,
about how traditional water pots made of copper or bronze helped keep
bacteria from growing in the water because of copper leaching into the
water:
I just heard about a study done in India (by Western
scientists) related to traditional copper water containers and water
safety. The Older (and wiser) folks in India always claimed that
copper and bronze container were safest to use as water containers
because the copper killed bacteria. Scientist have studied these pots
and have discovered that the small amounts of copper that leaches into
the water does in fact kill bacteria. The amounts are totally harmless
to humans, in fact, provide essential amounts of necessary dietary
copper in the diet.
Now, people in India are using cheaper plastic
containers and these do not kill bacteria. They don't use copper any
longer because it is expensive. I was wondering if pottery water
storage jars could be made at a low price with a copper liner glaze that
would do the same thing the old copper containers used to do, but sell
for less money? You could also more accurately control the rate of
copper release from the glaze and tune it to exactly the amount
needed. I wonder if Rex knows about this?
Makes me wonder if our replacing the copper plumbing in
our houses with PCV is a big health mistake?
--
Lee in Mashiko, Japan http://mashiko.org
http://hankos.blogspot.com/ Visual Bookmarks
"We can make our minds
so like still water
that beings gather about us
that they may see,...
....their own images, and so live for a moment with a clearer,
perhaps even with a fiercer life
because of our quiet." -- W. B. Yeats
Dave Finkelnburg on fri 15 apr 05
Vince and John Hesselberth have touched on what, to me, is the important point about crazing...it weakens the ware. To me, any health concern is totally subjective in mid to high-fired ware. Its significance is up to you to judge. Strength, however, is a major, and clear cut issue.
Testing has shown that crazed ceramics are 75 to 80% WEAKER than the same ceramics uncrazed. So, if you are making cups, bowls, plates or other ceramics subject to being bumped and bounced and eventually chipped and broken, glazing them with glazes that neither craze nor shiver can make that work dramatically more durable.
This doesn't mean crazed pots are doomed. Of course not! There are crazed pots that have survived for millenia. I just think if you are concerned about the durability of your work, and don't have specific, artistic reasons for introducing crazing into your work, you should consider crazing from a ceramic strength perspective.
Good potting!
Dave Finkelnburg
Vince Pitelka wrote:
As I have understood it all these years, in midrange and high-fired ware,
crazing is primarily a structural flaw.
---------------------------------
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Edouard Bastarache Inc. on fri 15 apr 05
Hello Vince
" I'm interested in the fact that crazing seems so inevitable in salt and
soda
firing, but I think I'll address that in another post.
- Vince"
Zillions of salt/soda fired pots have been used for centuries without
collective harm to zillions of people.
For instance, consider the people of Germany were salt firing was
invented centuries ago.
Later,
"Ils sont fous ces quebecois"
"They are insane these quebekers"
"Están locos estos quebequeses"
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
www.sorel-tracy.qc.ca/~edouardb/Welcome.html
http://perso.wanadoo.fr/smart2000/index.htm
http://www.digitalfire.com/education/toxicity/
Paul Lewing on fri 15 apr 05
on 4/14/05 6:18 PM, Linda Ferzoco at ltferzoco@YAHOO.COM wrote:
> There are germs that can survive live steam under
> 15-20 psi pressure for 30-60 minutes! This has been shown repeatedly, by
> design or accident, in laboratory settings.
Right, and they're just as unlikely to come stampeding out of the crazes in
glazes as normal bacteria.
Paul Lewing, Seattle
Cat Jarosz on fri 15 apr 05
In a message dated 4/15/2005 2:49:51 PM Eastern Daylight Time,
ben@THECOMMONPOT.COM writes:
I'm surprised no one has pointed out the fact that the absorption rates
for fired earthen ware are 10 -22%. I think there is a legitimate western
cultural aversion to crazed ware based in the predominance of earthenware
production and a lack common hygeine (i.e running water and sewerage) up
until the 19th c. I think early american stoneware production was not alway
so technical as to ensure vitrified bodys thus the popularity of albany slip
as a liner glaze.
I think Ben makes a really good point here with the vitrification. Cone 10
Stoneware was explained to me as a very tight clay body that really didnt
need a glaze to hold water. You used glazes to make it clean up easier and
it looks better.... Pretty simple terms .
Soo that makes you wonder about crazed glazes and germs... I understand
that some people believe that crazing can weaken the clay body but usually I
think of black coring as the culprit more than crazing. if the clay body is
solid and tight then why would crazing make a difference in germs ? At
least for cone 10 Stoneware and porcelain bodies?
I dont want to argue that crazing is great but I dont know that its that
bad either.. this is a good subject to discuss.
Cat Jarosz and Curly the clay
dog...
http://www.guildcrafts.com/cat/
V)''(V woof & >^..^< mew; Chicks with beards rule !!!
(_o_)
\||/
Edouard Bastarache Inc. on sat 16 apr 05
Vince,
I will ask Bernd Pfannkuche at
ceramics-consult@t-online.de
Later,
"Ils sont fous ces quebecois"
"They are insane these quebekers"
"Están locos estos quebequeses"
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
www.sorel-tracy.qc.ca/~edouardb/Welcome.html
http://perso.wanadoo.fr/smart2000/index.htm
http://www.digitalfire.com/education/toxicity/
Ron Roy on sat 16 apr 05
A properly fitting glaze on functional ware makes for a clearly superior
product on many levels.
I suspect the reason so many potters do not object to crazing is in direct
relationship to their ability to correct the fault.
RR
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Craig Carlyle Clarke on sat 16 apr 05
a couple of points...
First, growing up in TOO clean of an environment is suspected as a
cause of Crohn's Disease. You need to have an exposure to the
not-too-nasty buggers to develop a healthy immune system.
Also, I have heard of recent studies that say that wooden cutting
boards are actually safer than glass or plastic because they absorb
pathogens and "lock them away" rather than leaving them on the surface
- which you can NEVER get totally clean... could the same not be true
for unglazed ceramics?
I dunno.
- CCC
--=20
http://www.buffalog.com
John Britt on sat 16 apr 05
Ron,
I completely disagree with this statement.
On Sat, 16 Apr 2005 13:05:33 -0500, Ron Roy wrote:
>.....
>I suspect the reason so many potters do not object to crazing is in direct
>relationship to their ability to correct the fault.
>
>RR
>
There are many glazes (and glaze types) that cannot be cured of crazing
without a significant change to the character of the glaze. This is
independent of a person=92s ability to stop the crazing.
The most obvious example is Carbon Trap Shino. It will always craze
because there is soluble sodium present (highest exp/cont. of all the
oxides) which is brought to the surface through evaporation. This creates
a layer of high exp. /cont. oxide on the surface.
Correct me if I am wrong, but I thought I remember from your NCECA lecture
that you accepted crazing in shinos, including your version of a high
alumina orange shino which I thought you showed a slide of on a functional
plate.
You could also include other glaze types, most notably, copper red. Now I
know David Hendley and others have recipes or have adjusted recipes to
make them not craze or craze less often, but they cannot, in my opinion,
hold a candle to a real low alumina copper red.
I could also add other glaze types, including Goldstone, Kuan and
soda/salt glazes.
There are some Kuan=92s and blue crackle Kuan=92s that are exquisite and wou=
ld
be lost without the crazing. And anyone who makes salt and soda fired work
knows about the effects of a layer of soda on the surface of the pot.
I don=92t think it is always possible to stop crazing without loosing some
of the very properties you like in a glaze.
Just my opinion,
John Britt
www.johnbrittpottery.com
Ron Roy on sun 17 apr 05
Dear Louis,
I cannot say I use your bowl for tea every day - or ever for that matter -
I simply cannot get it to hold tea no matter how hard I try.
I do see it every day - and it still makes me smile every day - and it does
an exquisite job of holding my pencils.
To explain to all the other on this list - the tea bowl is made from clay
with all sorts of organic granular material wedged in - like sunflower
seeds. There are holes everywhere.
To add to Louis's comment on storing food on a crazed glaze - which I agree
with - I would also caution about serving smelly food like fish on such
ware - unless you enjoy smelling the fish for days and weeks after.
RR
>At the same time I think it wise not to store your meatloaf uncooked in
>a crazed vessel. Why tempt fate? Since the public cannot be expected to
>differentiate between their crazed and uncrazed ware, perhaps the
>conservative approach is to not sell crazed ware. In this sense I am
>conservative. At the same time Ron Roy got my well pocked teabowl a few
>years ago and I am sure he uses it daily:).
>Louis
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Lee Love on sun 17 apr 05
Des & Jan Howard wrote:
> That said a non porous, non absorptive cone 11-12 body with a crazing
> glaze has to be much stronger than for example
> a non crazed one at cone 6 ;-)
One of the great advantages of higher temps is lower absorption,
durability, wider range of glaze maturity, and the fact that you don't
have to use industrial fluxes to make durable glazes or non-porous
bodies. Primarily, at high fire, you are dealing with feldspar,
silica, clay and calcium in some form.
To turn an old programmer's term around a bit: "No garbage in,
no garbage out."
Also, the whole microwave/dishwasher safe aspect seems to be
one of lifestyle rather than health or safety. Here in Japan, I am
sure few people put their $5,000.00 tea bowl in a microwave or
dishwasher. ;-)
--
Lee in Mashiko, Japan http://mashiko.org
http://hankos.blogspot.com/ Visual Bookmarks
"We can make our minds
so like still water
that beings gather about us
that they may see,...
....their own images, and so live for a moment with a clearer,
perhaps even with a fiercer life
because of our quiet." -- W. B. Yeats
Vince Pitelka on sun 17 apr 05
----- Original Message -----
From: "Des & Jan Howard"
To:
Sent: Saturday, April 16, 2005 4:31 PM
Subject: Re: Is crazing always so terrible?
> Ron
> Stainless steel ware is so much stronger & more durable than ceramic
> ware so why do we bother making ceramic pots if a "superior" product is
> the goal?
> It is all about aesthetics not relative strengths.
> That said a non porous, non absorptive cone 11-12 body with a crazing
> glaze has to be much stronger than for example
> a non crazed one at cone 6 ;-)
> Des
>
> Ron Roy wrote:
>
>>A properly fitting glaze on functional ware makes for a clearly superior
>>product on many levels.
>>
>>I suspect the reason so many potters do not object to crazing is in direct
>>relationship to their ability to correct the fault.
>>
>>
>
> --
> Des & Jan Howard
> Lue Pottery
> LUE NSW 2850
> Australia
> Ph/Fax 02 6373 6419
> http://www.luepottery.hwy.com.au
>
> ______________________________________________________________________________
> 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.
>
John Hesselberth on sun 17 apr 05
Hi Des,
Could you give me a literature reference or quote your own data on
this? I think you will have a hard time supporting that statement, but
I'd be happy to be proved wrong.
Regards,
John
On Saturday, April 16, 2005, at 05:31 PM, Des & Jan Howard wrote:
> That said a non porous, non absorptive cone 11-12 body with a crazing
> glaze has to be much stronger than for example
> a non crazed one at cone 6 ;-)
Des & Jan Howard on sun 17 apr 05
Ron
Stainless steel ware is so much stronger & more durable than ceramic
ware so why do we bother making ceramic pots if a "superior" product is
the goal?
It is all about aesthetics not relative strengths.
That said a non porous, non absorptive cone 11-12 body with a crazing
glaze has to be much stronger than for example
a non crazed one at cone 6 ;-)
Des
Ron Roy wrote:
>A properly fitting glaze on functional ware makes for a clearly superior
>product on many levels.
>
>I suspect the reason so many potters do not object to crazing is in direct
>relationship to their ability to correct the fault.
>
>
--
Des & Jan Howard
Lue Pottery
LUE NSW 2850
Australia
Ph/Fax 02 6373 6419
http://www.luepottery.hwy.com.au
John Hesselberth on sun 17 apr 05
On Sunday, April 17, 2005, at 10:30 AM, Lee Love wrote:
> One of the great advantages of higher temps is lower absorption,
> durability, wider range of glaze maturity,
Hi Lee,
Please tell me some references for these points. I have seen cone 6
clay bodies with pretty low absorption and durability equal to cone 10.
I would also question the wider range of glaze maturity. Data or
references please.
Regards,
John
Eric Hansen on mon 18 apr 05
Properly fired ware can be up to 5 times stronger than that which isn't, ac=
cording to the Nigel Wood book which coincidentally I just happen to be rea=
ding at thistime. I guess it all depends on whether or not the ceramic obje=
cts made are intended to be used on not.
On the other hand I kind of wabi sabi about the idea of using a crackle rak=
u teabowl knowing that someday it will fall to pieces. But your customers m=
ight not appreciate the experience.
If you "put in your two cents worth"
but it's only "a penny for your thoughts"
who is keeping the extra penny?
E R I C=20=20
--=20
_______________________________________________
NEW! Lycos Dating Search. The only place to search multiple dating sites at=
once.
http://datingsearch.lycos.com
Jennifer Boyer on mon 18 apr 05
Just for the heck of it, a totally unscientific test: I had a glaze I
was working on that was a great color, but I could tell that the fit
was not good at all since the pots pinged like crazy after the firing.
It was mattish and it was hard to get a good look at the crazing
pattern in the glaze even with a magnifier. I used the bowls for a
couple of years since I liked the color. This winter I noticed that the
bowls were decidedly dull in tone when rung(like a bell) and knew that
they had cracks, but I couldn't tell where they were or how many. So I
decided to scientifically bonk them gently with a hammer to see what
cracking knowledge I might gain. It was actually quite interesting!
Gentle tapping broke them and I broke them
into small pieces. There didn't seem to be any preexisting cracks(I've
used cracked pots for years before they actually broke) but I did
notice areas where they broke with a jagged edge to the break. Other
areas broke in straighter lines. Clearly most of these bowls had
weakened areas. I'm not sure whether the glaze had crazed or
dunted....I'm suspecting dunting, but I definitely know that the glaze
weakened these bowls alot..
Take Care
Jennifer
On Apr 15, 2005, at 4:07 PM, Dave Finkelnburg wrote:
> Vince and John Hesselberth have touched on what, to me, is the
> important point about crazing...it weakens the ware. To me, any
> health concern is totally subjective in mid to high-fired ware. Its
> significance is up to you to judge. Strength, however, is a major,
> and clear cut issue.
>
> Testing has shown that crazed ceramics are 75 to 80% WEAKER than the
> same ceramics uncrazed. So, if you are making cups, bowls, plates or
> other ceramics subject to being bumped and bounced and eventually
> chipped and broken, glazing them with glazes that neither craze nor
> shiver can make that work dramatically more durable.
>
> This doesn't mean crazed pots are doomed. Of course not! There are
> crazed pots that have survived for millenia. I just think if you are
> concerned about the durability of your work, and don't have specific,
> artistic reasons for introducing crazing into your work, you should
> consider crazing from a ceramic strength perspective.
>
> Good potting!
> Dave Finkelnburg
>
> Vince Pitelka wrote:
> As I have understood it all these years, in midrange and high-fired
> ware,
> crazing is primarily a structural flaw.
>
> ---------------------------------
> Do you Yahoo!?
> Yahoo! Small Business - Try our new resources site!
>
> _______________________________________________________________________
> _______
> 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.
>
>
************************
Jennifer Boyer
Thistle Hill Pottery
Montpelier, VT
http://thistlehillpottery.com
Des & Jan Howard on mon 18 apr 05
John
I used the same references & data set as Ron's assertion, my methodology
did include tongue in right cheek as shown by the emoticon.
Des
John Hesselberth wrote:
> Hi Des,
>
> Could you give me a literature reference or quote your own data on
> this? I think you will have a hard time supporting that statement, but
> I'd be happy to be proved wrong.
--
Des & Jan Howard
Lue Pottery
LUE NSW 2850
Australia
Ph/Fax 02 6373 6419
http://www.luepottery.hwy.com.au
Lee Love on tue 19 apr 05
John Hesselberth wrote:
> I have seen cone 6 clay bodies with pretty low absorption and
> durability equal to cone 10.
Yes, we always compare to high fire along these lines. Stoneware
and porcelain are the reference for durability. The stoneware clays
(traditionally) come right out of the ground ready to go. But when
dealing with the middle temperatures, the clay formulas need to be
"calculated."
Clays here in Japan, because materials are not totally
focused on industry, come right out of the ground. Typically, the
only processing is blundging and filtering to get the rocks out. My
main clay, Mashiko Nami Tsuchi, is used as plugs for the stoke holes of
the noborigama. It is very durable clay.
So, to get back to the original subject: "Is crazing
always so terrible?" Sometimes crazing is acceptable. The main
problem with crazing is when you are working with absorbent claybodies
or typically, with lower fired glazes that contain problematic
materials.
--
Lee in Mashiko, Japan http://mashiko.org
http://hankos.blogspot.com/ Visual Bookmarks
"We can make our minds
so like still water
that beings gather about us
that they may see,...
....their own images, and so live for a moment with a clearer,
perhaps even with a fiercer life
because of our quiet." -- W. B. Yeats
Ron Roy on tue 19 apr 05
Hi Des - or is it Jan?
Stainless has it's place - and it's not all badly designed either.
If we don't build functionality, durability and balance into our
aesthetically superior pots - those we want people to use - then we are
hypocrites to start with and telling our customers they are better off with
stainless.
My point still is - what potter would do that if they could solve the problems?
If there are potters who do know how to solve the problems and they choose
not to - what would we call them?
I do agree there are certain minimum standards - non absorption would be in
that category - next on the list? Stable liner glazes? Next would proper
fitting glazes - what after that?
On a scale of 1 to 10 - where would smooth bottoms be?
I had better stop this - I'm beginning to enjoy it too much.
RR
>Ron
>Stainless steel ware is so much stronger & more durable than ceramic
>ware so why do we bother making ceramic pots if a "superior" product is
>the goal?
>It is all about aesthetics not relative strengths.
>That said a non porous, non absorptive cone 11-12 body with a crazing
>glaze has to be much stronger than for example
>a non crazed one at cone 6 ;-)
>Des
>
>Ron Roy wrote:
>
>>A properly fitting glaze on functional ware makes for a clearly superior
>>product on many levels.
>>
>>I suspect the reason so many potters do not object to crazing is in direct
>>relationship to their ability to correct the fault.
>Des & Jan Howard
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Anne Webb on wed 20 apr 05
hey des..
well i cant say i entirely agree with you there. Its not just about
aesthetics especially when it comes to functional pots. Part of the beauty
and appeal of pottery is that it is handmade, but you want your pots to be
able to work too, and work well. The design should not only be aesthetically
pleasing but practical as well. If that teapot breaks your wrist when you
try to pour, it doesnt really matter how pretty it is.. its not functional.
Same goes for glaze fit. Who wants bits of that pretty glaze popping off
into their ice cream because the glaze wasnt formulated right?
While i do agree that a high fire pot is more durable than a cone 6 one,
when your glaze fits right, it makes for a strong and even more durable pot
than if your glaze didnt. No brainer. This is especially important for
functional ware as it needs hold up under the rigors of daily use.
Ron isnt saying go out there and make sterile bland looking pots, just ones
that work. And whats wrong with that? Seems pretty logical to me.
Sometimes its too easy to get caught using the guise of something being
'handmade' as an excuse for shortcomings in design and functionality, but it
doesnt have to be that way.
anne
Des Howard wrote
>
>Ron
>Stainless steel ware is so much stronger & more durable than ceramic
>ware so why do we bother making ceramic pots if a "superior" product is
>the goal?
>It is all about aesthetics not relative strengths.
>That said a non porous, non absorptive cone 11-12 body with a crazing
>glaze has to be much stronger than for examp non crazed one at cone 6 ;-)
>Des
>
>Ron Roy wrote:
>
>>A properly fitting glaze on functional ware makes for a clearly superior
>>product on many levels.
>>
>>I suspect the reason so many potters do not object to crazing is in direct
>>relationship to their ability to correct the fault.
>>
_________________________________________________________________
Don’t just search. Find. Check out the new MSN Search!
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John Hesselberth on wed 20 apr 05
On Wednesday, April 20, 2005, at 02:06 PM, Anne Webb wrote:
> While i do agree that a high fire pot is more durable than a cone 6
> one,
> when your glaze fits right,
Hi Anne,
I do not believe this statement is accurate. They are equal if the clay
bodies are well formulated and the glazes fit. Kat (in the Hat) of
Plainsman Clays reported her data just a couple days ago that confirms
it for porcelain. This concern that cone 6 bodies are somehow inferior
to cone 10 is just not accurate. And either can be poorly formulated or
have glaze fit problems.
Regards, John
John Jensen on wed 20 apr 05
John H;
Not to be disputatious: I would like to know. Isn't a cone 14 porcelain
(properly formulated and fired) stronger than a (properly formulated and
fired) cone 6 stoneware clay. Or to put the question another way: Is the
strongest known material in common usage fired at a higher temperature than
materials of lesser strength. Inquiring minds want to know.
John Jensen, Mudbug Pottery
John Jensen@mudbugpottery.com
http://www.toadhouse.com www://www.mudbugpottery.com
>Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of John
Hesselberth
ht,
Hi Anne,
This concern that cone 6 bodies are somehow inferior
to cone 10 is just not accurate. And either can be poorly formulated or
have glaze fit problems.
Regards, John
pdp1@EARTHLINK.NET on thu 21 apr 05
Hi John,
You mention...
----- Original Message -----
From: "John Hesselberth"
> Aramid fibers (Kevlar is an example) is 6 times
> stronger than steel on an equal weight basis.
>
> Regards,
>
> John
You may mean in tension, tensile strength, maybe...
But we all often hear about how something is 'stronger' than
something else, and in order for it to mean anything, it
helps if we may know in what way, or in what kind of
situation. Tensile strength is not allways the most
important kind of strength for a given situation. A Spider's
web or a single
strand of Catapillar Silk, on the same basis, is likely a
great deal stonger yet, than Kevlar...but neither woud make
a very good Truck or Car Wheel for one's Tire to go on...it
would not make a very good Ship's Hull for deep water
Freighters...
How is Kevlar in 'compression'?
I do not believe that of the great many things which exist
that are made of Steel, that very many of them would be
'better' if made from the 'stonger' kevlar...or that very
many of them would anylonger even function at all if they
were.
Can we expect Kevlar 16 Penny Nails to be stronger than
Steel ones?
I can not imagine large Kevlar Rivets holding together large
Kevlar, Wide-Flange Beams for Rail Road Bridges, for
example...for Kevlar Locomotives and Freight Cars to cross
upon...on Kevlar Rails...on Kevlar Wheels...
Anyway...
Just some fun...
I would imagine, that in practice, extrinsicly, our Pots are
more subject to compression forces, than to those of
Tension,
while intrinsicly, both or either may tend to exist, or to
exist at the same time, in them.
Phil
el ve
John Hesselberth on thu 21 apr 05
On Wednesday, April 20, 2005, at 10:27 PM, John Jensen wrote:
> Not to be disputatious: I would like to know. Isn't a cone 14
> porcelain
> (properly formulated and fired) stronger than a (properly formulated
> and
> fired) cone 6 stoneware clay. Or to put the question another way: Is
> the
> strongest known material in common usage fired at a higher temperature
> than
> materials of lesser strength. Inquiring minds want to know.
Hi John,
I have never seen any data that would prove that. Have you? I see no
theoretical reason why it should be so. Your last statement is
certainly not true. Aramid fibers (Kevlar is an example) is 6 times
stronger than steel on an equal weight basis. The processing
temperature is much, much lower. It is not 'fired' at all. Spider silk
is an exceptionally strong material. It also has amazing elastic
properties. Truly a fascinating material. Processing
temperature--ambient.
Regards,
John
John Jensen on thu 21 apr 05
Well John;
I'm not a big in-depth-research kind of guy, but I guess all the general
pottery books I read in my earlier days suggested that high fired porcelain
was stronger than stoneware and stoneware was stronger than earthenware. I
have some Danish porcelain which has been amazingly durable.
As far as the aramid/kevlar/spiderweb comparison goes...I meant commonly
used ceramic materials. But I guess you knew that.
Is Earthenware also as strong as porcelain, when properly formulated?
John Jensen, Mudbug Pottery
John Jensen@mudbugpottery.com
http://www.toadhouse.com www://www.mudbugpottery.com
John Hesselberth on fri 22 apr 05
On Thursday, April 21, 2005, at 04:29 PM, John Jensen wrote:
> I guess all the general
> pottery books I read in my earlier days suggested that high fired
> porcelain
> was stronger than stoneware and stoneware was stronger than earthenware
Hi John,
And that may be true. I think the question is whether cone 10 or 12
stoneware is stronger that cone 6 stoneware. And whether cone 14
porcelain is stronger than cone 6 porcelain. My point is that it is
composition and degree of vitrification that is important.
Vitrification can be achieved at various temperatures. Earthenware is,
of course, not vitrified and is generally recognized as being weaker
and more prone to chipping.
Regards,
John
John Hesselberth on fri 22 apr 05
Also please read Jonathan's post on this subject. He says it much
better than I.
John
On Thursday, April 21, 2005, at 04:29 PM, John Jensen wrote:
> Is Earthenware also as strong as porcelain, when properly formulated?
Lee Love on sat 23 apr 05
On Thursday, April 21, 2005, at 04:29 PM, John Jensen wrote:
> I guess all the general pottery books I read in my earlier days
> suggested that high fired porcelain was stronger than stoneware and
> stoneware was stronger than earthenware
John, I think part of it depends upon what kind of "strong" you
are talking about too. For example, traditional flameware is often
earthenware. My Mashiko nami clay is used to make plugs for
noborigama stoke holes.
Like I mentioned previously, traditionally, stoneware was
taken right out of the ground and used as is, only wet filtering to get
the gravel out. Something that is very interesting that folks
might not be aware of if they have always only used factory/refined clay
for their clay body: in many tradtional clay bodies, while the
clay can be relatively thick, the pot feels lighter overall. How
could this be? Because organics in the clay burn out and leave some
spaces in the clay. I am guessing this is one reason mashiko nami
can be used for stoke hole plugs and stand up the the heat shock. No
cone six factory formulated clay could take the temperature, let alone
the heat shock.
--
Lee in Mashiko, Japan http://mashiko.org
http://hankos.blogspot.com/ Visual Bookmarks
"We can make our minds
so like still water
that beings gather about us
that they may see,...
....their own images, and so live for a moment with a clearer,
perhaps even with a fiercer life
because of our quiet." -- W. B. Yeats
John Jensen on sat 23 apr 05
Lee,
What kind of Strong I'm talking about is the kind of strong that makes a
difference when you are washing dishes and the dish slips out of your hand
and bumps against another dish. The kind of strong that when you bang the
edge of the dish against the sink it doesn't crack into pieces. I just
always thought porcelain was inherently stronger than stoneware, but it
seems I may be wrong about this. Maybe porcelain has the reputation for
being stronger because people who make it are somehow more careful to
formulate and fire it correctly.
Do you think the spaces in the stoneware clay you mentioned serve to make
it stronger or weaker?
John Jensen, Mudbug Pottery
John Jensen@mudbugpottery.com
http://www.toadhouse.com www://www.mudbugpottery.com
On Thursday, April 21, 2005, at 04:29 PM, John Jensen wrote:
> I guess all the general pottery books I read in my earlier days
> suggested that high fired porcelain was stronger than stoneware and
> stoneware was stronger than earthenware
John, I think part of it depends upon what kind of "strong" you
are talking about too. For example, traditional flameware is often
earthenware. My Mashiko nami clay is used to make plugs for
noborigama stoke holes.
Something that is very interesting that folks
might not be aware of if they have always only used factory/refined clay
for their clay body: in many tradtional clay bodies, while the
clay can be relatively thick, the pot feels lighter overall. How
could this be? Because organics in the clay burn out and leave some
spaces in the clay--
Lee in Mashiko, Japan http://mashiko.org
http://hankos.blogspot.com/ Visual Bookmarks
Liz Willoughby on sat 23 apr 05
Hello Claybuds,
I have no idea which clay is the strongest; earthenware, stoneware,
or porcelain, and whether the firing temp. has anything to do with
the strength, or whether the formulation of the clay has anything to
do with it either. But. . . . .
this is what recently happened to me. I was washing up dishes in the
sink (always full of hand-made work, all kinds, and accidently banged
VERY HARD a Tom Coleman tea bowl on the faucet. I could not believe
that it survived, completely intact. This tea bowl is about 10 years
old and is incredibly thin, and translucent with a celadon glaze (not
at all crazed) and has C P on the bottom, which means that it is
Coleman Porcelain. It is wonky, lots of stamp decoration, which I
would think make it weaker.
I believe that most pottery certainly would not have survived the banging.
Just to confuse people more,
Meticky Liz from Grafton, Ontario, Canada.
April Showers Bring May Flowers
>Lee,
>What kind of Strong I'm talking about is the kind of strong that makes a
>difference when you are washing dishes and the dish slips out of your hand
>and bumps against another dish. The kind of strong that when you bang the
>edge of the dish against the sink it doesn't crack into pieces. I just
>always thought porcelain was inherently stronger than stoneware, but it
>seems I may be wrong about this. Maybe porcelain has the reputation for
>being stronger because people who make it are somehow more careful to
>formulate and fire it correctly.
> Do you think the spaces in the stoneware clay you mentioned serve to make
>it stronger or weaker?
>John Jensen, Mudbug Pottery
Ron Roy on sun 24 apr 05
The reason clay fired above 1100 C is stronger than earthen ware is because
mullite grows above that temperature. Mullite is needle shaped crystals
which interlock with the other components of a clay body and provide
mechanical strength. It is why stoneware and porcelain resists chipping so
much better than earthenware.
To say that the best high fired porcelain can be stronger than the best
stoneware may be true - I do not know that - and would not assume that many
of the pottery books were written by people who were deep researchers - so
I would not use them to tell me if it were so.
We should also include the glazes in the equation - glaze fit is a very
important part of the story.
RR
>Well John;
>I'm not a big in-depth-research kind of guy, but I guess all the general
>pottery books I read in my earlier days suggested that high fired porcelain
>was stronger than stoneware and stoneware was stronger than earthenware. I
>have some Danish porcelain which has been amazingly durable.
>As far as the aramid/kevlar/spiderweb comparison goes...I meant commonly
>used ceramic materials. But I guess you knew that.
>Is Earthenware also as strong as porcelain, when properly formulated?
>
>John Jensen, Mudbug Pottery
>John Jensen@mudbugpottery.com
>http://www.toadhouse.com www://www.mudbugpottery.com
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
JoyceLee on sun 24 apr 05
ok
>
> From: Lee Love
> Date: 2005/04/24 Sun PM 04:22:18 PDT
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Re: Is crazing always so terrible?
>
> John Jensen wrote:
>
> > Do you think the spaces in the stoneware clay you mentioned serve to make
> >it stronger or weaker?
> >
> Sometimes. :-) Of course, thicker edges give more
> strength there. But there are many other advantages, such as
> insulation quality , not to mention the surface variations you don't
> find in industrial sourced clay. The single biggest criticism I could
> make of cone 6 electric is that it is frequently too uniformed and
> controlled. I don't think it has to be that way, but typically ends
> up that way because its main source of inspiration is industrially mass
> produced derived processes.
>
> I know the work I make now is physically stronger than
> the work I used to make back home. A couple issues I think are far
> more important in high temp stoneware for strength than crazing, are:
> the form of the pot (even walls, etc) and also how you dry and fire the
> work.
>
> With traditional ware, because of the variety of
> firing temps in the large woodfire kilns, the most frequent source of
> weak pots is underfiring. Some of the pots, traditionally, don't get
> over cone 1. But, if you go through the Hamada museum, most of his
> more interesting glazes, especially the nukas, look the way they do
> because they are underfired. I realized this from firing student
> pots in my teacher's noborigama. The deshis put most of their work on
> the floor, under the last shelves where it was very cold. Our student
> pots tended to have soft, mat surfaces like Hamada's.
>
> I like temperature variation in a kiln for the
> variation it adds. When you let go of come control, the kiln
> sometimes makes "happy accidents." I deal with the strength problem
> by having the variation go from cone 9 to cone 14, putting Mashiko nami
> tsuchi in the cooler areas and unglazed Shigaraki and shino-type glazes
> in the hotter areas.
>
> --
> Lee in Mashiko, Japan http://mashiko.org
> http://hankos.blogspot.com/ Visual Bookmarks
>
> "We can make our minds
> so like still water
> that beings gather about us
> that they may see,...
> ....their own images, and so live for a moment with a clearer,
> perhaps even with a fiercer life
> because of our quiet." -- W. B. Yeats
>
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>
Lee Love on mon 25 apr 05
John Jensen wrote:
> Do you think the spaces in the stoneware clay you mentioned serve to make
>it stronger or weaker?
>
Sometimes. :-) Of course, thicker edges give more
strength there. But there are many other advantages, such as
insulation quality , not to mention the surface variations you don't
find in industrial sourced clay. The single biggest criticism I could
make of cone 6 electric is that it is frequently too uniformed and
controlled. I don't think it has to be that way, but typically ends
up that way because its main source of inspiration is industrially mass
produced derived processes.
I know the work I make now is physically stronger than
the work I used to make back home. A couple issues I think are far
more important in high temp stoneware for strength than crazing, are:
the form of the pot (even walls, etc) and also how you dry and fire the
work.
With traditional ware, because of the variety of
firing temps in the large woodfire kilns, the most frequent source of
weak pots is underfiring. Some of the pots, traditionally, don't get
over cone 1. But, if you go through the Hamada museum, most of his
more interesting glazes, especially the nukas, look the way they do
because they are underfired. I realized this from firing student
pots in my teacher's noborigama. The deshis put most of their work on
the floor, under the last shelves where it was very cold. Our student
pots tended to have soft, mat surfaces like Hamada's.
I like temperature variation in a kiln for the
variation it adds. When you let go of come control, the kiln
sometimes makes "happy accidents." I deal with the strength problem
by having the variation go from cone 9 to cone 14, putting Mashiko nami
tsuchi in the cooler areas and unglazed Shigaraki and shino-type glazes
in the hotter areas.
--
Lee in Mashiko, Japan http://mashiko.org
http://hankos.blogspot.com/ Visual Bookmarks
"We can make our minds
so like still water
that beings gather about us
that they may see,...
....their own images, and so live for a moment with a clearer,
perhaps even with a fiercer life
because of our quiet." -- W. B. Yeats
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