Gavin Stairs on sun 28 jul 02
At 03:25 PM 27/07/2002, Francoise wrote:
>... I ... (filled) it with cold water and (put) it on my gas cooker. I
>let it come to a boil and left it simmering for about 15 minutes. Yes, no
>nasty surprises, and I am here to tell the tale! I removed the dish from
>the flame, emptied out the boiling water, rinsed it in cold water and
>inspected it for crazing, etc. Nada. Looks just as it did when I removed
>it from the kiln. ...
Dear Francoise,
Most clay will survive the test you have described. In fact, most clay
vessels will serve very well as cooking pots. People living in primitive
circumstances have used plain earthenware pots for cooking over fires for a
very long time. For the most part, they serve very well.
In the discussion below, you can probably substitute US for developed
country without going much wrong.
The reason so-called flame ware is problematic in developed countries,
particularly those with developed legal systems, is the heightened risk of
liability in case of misuse or mistreatment of the ware, and subsequent
injury to the user, with consequent suit for damages. In a contemporary
kitchen using an electric range with metal burners and an enameled metal
stove top, it is quite easy to contrive such a misuse. First, the metal
burner is capable of inducing quite severe thermal gradients. Next, if the
pot is set down on a cold metal surface after heating, there will be even
greater stresses. Next, if the hot pot is brought into contact with cold
water... etc.
The legal problem arises out of the implied warrant of merchantability,
which is legalese for the assumption of the buyer that the pot will behave
as an ordinary person might expect it to. In developed countries, common
sense about clay vessels has atrophied to the point that few people
understand the limitations of such vessels, and consequently expect them to
survive being boiled dry, or heated dry, etc. The courts tend to side with
the plaintiffs, which means that it is a considerable risk to make the
claim that a clay vessel is suitable for cooking on a stove top. The
courts presumably take this position in order to protect the public from
its own ignorance as much as to punish makers of faulty ware.
The end result is that manufacturers, in North America at least, tend to
avoid the risk by declining to market such ware. There was a period during
which various attempts were made to design suitable bodies and
techniques. Out of this came cordierite ware, high lithia ware, and
various kinds of borate glass, culminating in the rather wonderful
recrystallized glass ceramics. Many of these vessels were tested with very
severe protocols, such as heating to red and quenching, or heating to
boiling and then placing on a cold metal plate, etc.
Few of these wares are still available for stovetop use. I only see borate
glass boiling vessels anymore. This is presumably because people have not
lost the expectation that a glass vessel might be fragile, as they seem to
have about opaque ceramics. The coffee pots normally bear baked on frit
declarations about the proper use of the pot: use a burner trivet or pad,
do not heat dry, discard if cracked or if boiled dry, etc. Ovenware on the
other hand is still available, presumably because it is less likely to
injure should a failure occur, and heating stress is normally less severe.
All this for the risk to life and limb should a pot full of boiling water
come apart in the hand of some person. This is a not inconsiderable
risk. I can recall at least two personal instances of a clay pot breaking
under normal use, as well as several failures of ceramic and glass coffee
pots under duress. I am 56 years old, so my experience means that most
people who use clay ware can expect to experience such a failure at least
once during their lives. How many would experience a severe injury? How
many would sue?
So, that in a nutshell is why there is discussion about flameware clay
body, and why it is generally unavailable in North America. And that is
why your flameware test result is no surprise. If such wares are commonly
available in Spain, then the assumptions of the implied warranty are
probably such that the risk is slight, both to the buyers and to you. If
you intend to make ovenware, then you are on fairly secure ground. If you
intend to make stovetop boilers, that is more of a risk.
I urge you to do your stove top tests on every form you intend to
market. It would be a good idea to make the test more severe, for instance
by refrigerating the pot and water before placing on the stove, or even
freezing it, if that would not crack the pot. If your pot will survive a
severe test, then you have greater assurance that it will survive ordinary
usage. You should always test in a more severe manner than you claim the
ware will survive in ordinary use. I would also advise you to print up a
little card to insert in each pot with instructions about what not to
do. In the event that you would be sued for selling dangerous goods, your
tests and warnings would be a defence, showing that you took measures to
ensure that your ware would survive ordinary use, and that the buyer was
made aware of the limitations of proper use.
All the best, Gavin
Earl Brunner on sun 28 jul 02
The other thing is that in these situations, we might be talking about
apples and oranges, or trying to compare two unlike materials and
applying the same conditions or results to them.
I think that the flameware talked about below is the high temperature
"fused" often lithium based ware that was made for a while as stove top
ware. (at least everything said in this instance I have heard
specifically about this type of pottery)
If it is made still at all, it is probably done in such a way that would
be difficult to reproduce in a studio potter setting.
The earthenware pottery that has for millennia been made and used over
an open flame by virtually every culture that has ever made pottery,
deals with uneven heat and thermal expansion in an entirely different
way (or at least the factures that prevent vitrified ware from
surviving) than more "sophisticated" ware. Even so, at least here in the
U. S. I would be hesitant about promoting the use of earthenware that I
had made in this manner. This society has become too litigious.
Earl Brunner
mailto:bruec@anv.net
http://coyote.accessnv.com/bruec
-----Original Message-----
From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG] On
Behalf Of Gavin Stairs
Sent: Sunday, July 28, 2002 7:52 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: flameware trial: long
At 03:25 PM 27/07/2002, Francoise wrote:
>... I ... (filled) it with cold water and (put) it on my gas cooker.
I
>let it come to a boil and left it simmering for about 15 minutes. Yes,
no
>nasty surprises, and I am here to tell the tale! I removed the dish
from
>the flame, emptied out the boiling water, rinsed it in cold water and
>inspected it for crazing, etc. Nada. Looks just as it did when I
removed
>it from the kiln. ...
Dear Francoise,
Most clay will survive the test you have described. In fact, most clay
vessels will serve very well as cooking pots. People living in
primitive
circumstances have used plain earthenware pots for cooking over fires
for a
very long time. For the most part, they serve very well.
In the discussion below, you can probably substitute US for developed
country without going much wrong.
The reason so-called flame ware is problematic in developed countries,
particularly those with developed legal systems, is the heightened risk
of
liability in case of misuse or mistreatment of the ware, and subsequent
injury to the user, with consequent suit for damages. In a contemporary
kitchen using an electric range with metal burners and an enameled metal
stove top, it is quite easy to contrive such a misuse. First, the metal
burner is capable of inducing quite severe thermal gradients. Next, if
the
pot is set down on a cold metal surface after heating, there will be
even
greater stresses. Next, if the hot pot is brought into contact with
cold
water... etc.
The legal problem arises out of the implied warrant of merchantability,
which is legalese for the assumption of the buyer that the pot will
behave
as an ordinary person might expect it to. In developed countries,
common
sense about clay vessels has atrophied to the point that few people
understand the limitations of such vessels, and consequently expect them
to
survive being boiled dry, or heated dry, etc. The courts tend to side
with
the plaintiffs, which means that it is a considerable risk to make the
claim that a clay vessel is suitable for cooking on a stove top. The
courts presumably take this position in order to protect the public from
its own ignorance as much as to punish makers of faulty ware.
The end result is that manufacturers, in North America at least, tend to
avoid the risk by declining to market such ware. There was a period
during
which various attempts were made to design suitable bodies and
techniques. Out of this came cordierite ware, high lithia ware, and
various kinds of borate glass, culminating in the rather wonderful
recrystallized glass ceramics. Many of these vessels were tested with
very
severe protocols, such as heating to red and quenching, or heating to
boiling and then placing on a cold metal plate, etc.
Few of these wares are still available for stovetop use. I only see
borate
glass boiling vessels anymore. This is presumably because people have
not
lost the expectation that a glass vessel might be fragile, as they seem
to
have about opaque ceramics. The coffee pots normally bear baked on frit
declarations about the proper use of the pot: use a burner trivet or
pad,
do not heat dry, discard if cracked or if boiled dry, etc. Ovenware on
the
other hand is still available, presumably because it is less likely to
injure should a failure occur, and heating stress is normally less
severe.
All this for the risk to life and limb should a pot full of boiling
water
come apart in the hand of some person. This is a not inconsiderable
risk. I can recall at least two personal instances of a clay pot
breaking
under normal use, as well as several failures of ceramic and glass
coffee
pots under duress. I am 56 years old, so my experience means that most
people who use clay ware can expect to experience such a failure at
least
once during their lives. How many would experience a severe injury?
How
many would sue?
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