John Baymore on thu 28 may 98
------------------
(clip)
............. looking through the Smith and Hawken Catalog last week and was
disturbed to find =2ACrackleware=2A for sale. It is cast work, badly crazed.
The comment says that a deliberate mismatch between the clay and glaze
creates the decorative crackling. It says that because it is fired at a
high stoneware heat, it is safe to use
for food. (snip) ........... called Smith and Hawkins, saying she was
unhappy ............ (clip) ............. has been a potter for twenty five
years and that she is sure
that a crackled glaze should not be used for food. (zap) ......... They
wanted to know why she was concerned. (slice) .............. The
translator said that she just didn't understand... that this is STONEWARE,
and stoneware is NON POROUS=21=21=21 And furthermore, it has been fired to =
1280c.
She responded that stoneware fired at that temp IS still porous... (snip)
.........Then their argument changed to say that the cracking is only on the
top layer of glaze and doesn't go all the way down to the clay body. She
told him she didn't believe him=21=21 And besides, she said, the crackle =
would
still be next to the food, and that would still make it good bacteria
breeding
grounds.
(clip)
WOW. Sounds like the comments caught the attention of their lawyers=21 =
Tell
her to be careful what and where she expresses these concerns other than
directly to them ....... they might feel that if the allegations prove
legally unsubstantiated that there is reason to hold her accountable for
any lost sales revenues and/or the costs of countering =22public =
preception=22
created by her comments.
..
That being said..........
In a broad generalization.... stoneware is non-porous. Certainly when
compared to earthenware. The reality however is that it probably is
minimally porous. This porosity depends on the body formulation and
firing. How porous is that particular body? Only way to tell for sure is
testing. A typical tight stoneware might have a open pore absorbtion test
of .5-.75=25 weight change. I have seen =22stoneware bodies=22 that have =
far
higher absorbtion figures......... these are more porous. But still really
minimally so.
The exact definition of =22stoneware=22 is elusive........ clay that is
=22stone-like=22. There's lots of types of stones (g).
So it does have some porosity. But if it is a reasonable body, this is so
slight that it is, for all intents and purposes, effectively =
=22non-porous=22.
Compared to a silica glass container it might be considered slightly
porous. Compared to a red clay flowerpot.... it isn't.
Well fired stoneware is tight enough that the porosity is such that it
poses very little hazard from the growth of bacteria in the pores. Not NO
HAZARD...... just very little. You can probably use an unglazed mug for
your coffee (with cream) with reasonable impunity..... the statistical odds
are pretty slight that you might get sick from the bacteria that COULD grow
in the pores of the stoneware.
However...... if you are that one in a gazillion statistical loser, you
WILL get sick.
(=22Do you feel lucky, punk?=22 =3Cg=3E)
Now on to the crazing.
The cracks in the glaze are in the glaze, not the body. They extend
slightly into the boundary interface layer that develops in stoneware where
it's not really glaze and it's not really body. So you have a series of
miniscule cracks sitting basically over the surface of a pretty non-porous
clay body. The tech guy from the catalog was correct certainly in one
respect ....... the cracks are on the surface.
These cracks ARE sites that bacteria COULD hide and grow in. No question
of that. Most USA health departments won't allow crazed ware for use in
the food and beverage serving industry. Compared to a non-crazed surface,
the possibility of potential bacteria growth is much higher.
So the topic comes up of how much risk is too much risk? How mush risk
must there be to say something is not safe for food? How sick would one
typically get from such bacteria? How often would it happen?
If one is of the mindset that a single case of diarea in a single person in
an infinite time period is too much risk, then they just ought to quit
pottery......... cause if that concerns them then there are myriad other
risk factors in the field that must be at least as unacceptable.
Personally, I'd be more concerned about formulation of a base glass and the
oxides it contains that might leach into food than about the possibility of
significantly lethal bacteria growing in craze lines. Soft and leachable
glaze formulas is a far more common problem, I think, from looking at the
glaze formulas in use out in the world. I'd also be more concerned about a
bodys' resistance to thermal shock........ because shattering teapots and
mugs are more of a reality, and can cause significant sudden injury.
Yes..... crazed glaze provides a possible site for bacteria growth when
compared to a totally non-porous surface. (So do other common porous food
prep items such as cutting boards, pizza stones, red-clay cookers and bread
pans, ad nauseaum.) But the odds of that happening at a level to cause
significant illness or death are so slight... so minisclue.... that it is
probably not a significant concern. The history of pottery use is such
that crazed stoneware and porcelain glazes have been and STILL ARE in
widespread use all over the world.... yet there is little documentation of
a significant epidemic of adverse situations.
I am sure that it happens...... and that it is usually never traced to the
actual sorurce. But it is apparently not fequent nor severe. Has anyone in
the history of the world ever died from this? Most likely. But to keep it
in perspective......... your airbag in your car which is intended to save
you can kill you too.
If you don't WASH stuff properly........ well that is a real problem even
if it is glazed. If you store (e-coli contaminated) raw meat in a bowl and
then just quickly rinse it and put food back into it.... well you might
have a problem whether it is crazed or not crazed. That is a hygiene
issue... not a pottery issue.
Technically...... crackle (crazing) is less hygienic than non-crazed
glazes. How much of a hazard is it? Pretty small, I think. Should one be
concerned? Yes. If you can get the effects you want and get the glaze to
fit the body.... GREAT. Should you give up ALL glazes that craze for food
use? Only the individual potter can decide how they feel about this,
unless they are working in a venue where there are regulations published.
Then someone else decides.
Personally, I still use my ash glazes and shino glazes on food vessels.
They craze. I have no ethical issue with this....... as I would have if I
were to use saturated manganese glazes with micro-crystaline surfaces,
barium matts with high copper additions, cadmium reds, lead as a flux, and
so on. These are all actions that IMO, pose a more significant risk to
the consumer.
It is a factor of the magniutude of risk. You cannot sterilize life. Life
is full of risks.
Best,
........................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752
JBaymore=40Compuserve.com
Deanna Grant on fri 29 may 98
Thanks to John Baymore for that essay on crazing and the "dangers" therein. I am
a potter, but I am primarily a biologist. John makes an excellent point about
hygeine. It takes a while before bacteria are at a high enough concentration to
cause intestinal malfunction. The best way to avoid bacterial growth is to wash
your pottery with soap and HOT water. The hot water kills the bacteria (and
washes them away) and the soap breaks apart the bacterial cell walls.
I can also tell you that I've empirically tested this by way of my coffee (and
cream) cup which is crazed and which I simply rinse most of the time. I have
not gotten food poisoning by way of this mug for a number of years.
So, if you're going to buy dishes that are crazed for the purpose of your own
home...great! However, if you are relying upon other people to reliably wash
dinner ware for a restaurant and you do not have a standard sterilization
protocol to wash massive amounts of dinner ware, I wouldn't gamble on that one
in a million chance that a customer may get sick. But, I think the likelihood
of someone getting sick by the food...or as John made the point ...by heavy
metals leaching into the foods from the glazes...is far greater.
One other point...one should be careful about running to large corporations and
slandering their product without being 100% sure what one is talking about. I
found the dialog between the accuser and the French company to be awfully rash
and unsubstantiated.
Cheryl L Litman on sat 30 may 98
Deanna,
>I have
>not gotten food poisoning by way of this mug for a number of years.
Do you mean to say that you DID get food poisioning via the mug at one
time? At a time before you washed more carefully?
Cheryl Litman
Somerset, NJ
email: cheryllitman@juno.com
On Fri, 29 May 1998 12:39:36 EDT Deanna Grant
writes:
>----------------------------Original
>message----------------------------
>Thanks to John Baymore for that essay on crazing and the "dangers"
>therein. I am
>a potter, but I am primarily a biologist. John makes an excellent
>point about
>hygeine. It takes a while before bacteria are at a high enough
>concentration to
>cause intestinal malfunction. The best way to avoid bacterial growth
>is to wash
>your pottery with soap and HOT water. The hot water kills the
>bacteria (and
>washes them away) and the soap breaks apart the bacterial cell walls.
>
> I can also tell you that I've empirically tested this by way of my
>coffee (and
>cream) cup which is crazed and which I simply rinse most of the time.
>
>So, if you're going to buy dishes that are crazed for the purpose of
>your own
>home...great! However, if you are relying upon other people to
>reliably wash
>dinner ware for a restaurant and you do not have a standard
>sterilization
>protocol to wash massive amounts of dinner ware, I wouldn't gamble on
>that one
>in a million chance that a customer may get sick. But, I think the
>likelihood
>of someone getting sick by the food...or as John made the point ...by
>heavy
>metals leaching into the foods from the glazes...is far greater.
>
>One other point...one should be careful about running to large
>corporations and
>slandering their product without being 100% sure what one is talking
>about. I
>found the dialog between the accuser and the French company to be
>awfully rash
>and unsubstantiated.
>
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