Cheryl Shoemaker on sat 7 mar 98
>person who leaves coleslaw in a black bowl overnight? Or the person who
>"always " has a cup fo black coffee in a black cup at her elbow, or a
>black goblet of red wine beside him as he watches TV all evening.
>
>Prevention is much better than cure, Brad; and risk taking is just that.
Lili,
I apologize for not knowing the entirety of this thread, just caught this
while skimming after return from a road trip and could not let this go.
I agree re: risk taking concerning glazes ... but let's not put everyone
into a total panic when they see functional ware glazed black. If I had to
choose between making everybody think it was OK to sloppily concoct black
glazes and not bother to have them tested OR scare them so bad they'd never
consider it ... I'd definitely take your message to the masses but it's too
broad a statement. Let's make it clear that there ARE responsible potters
out there who use black glaze on functional ware and have it tested every
time a material changes, firing methods/times change etc. etc.
Want to know if a black glaze is food safe? Have a standard leach test done
on it at a certified lab for EVERY metal oxide used and any other toxic
ingredient. It's pretty simple really, put your money where your glaze
desire is and have it tested ...and tested repeatedly as warranted due to
material changes, firing changes etc. It's a lot of work but it can be done.
I think the problem lurking on the edge of your statement that may not have
been addressed is that people seem to want a "recipe" for a black glaze that
they can call food safe without bothering to have it tested. Therein lies
the big problem. It's my strong opinion that black glazes are achievable
for food surfaces if you:
a.) formulate one to your specifications (or find one in a recently
published book that has the characteristics you want and is supposedly food
safe)
b.) do glaze tests to find/use the least toxic metal oxides in the
smallest percentages possible, read up on glaze safety .. current info
c.) have a standardized leach test done @ a certified lab before you
put it on any food surface and keep an eye on the glaze ... The hard part
is once you get the numbers you may feel you have nothing to compare to,
where there are no numbers from FDA for dinnerware there are US EPA drinking
water standards to compare to (these are more stringent numbers to comapre
to indeed) and you can contact Arts, Crafts & Theater Safety, Inc and/or
Center for Safety in the Arts for advice too
d.) keep tight controls on your firings
e.) have it retested as conditions change.
If you're in someone's booth full of black glazed functional ware and want
to know if it's safe. ASK them about it. If they are bothering to go thru
testing etc. they will probably happily tell you about the leach tests done
and the oxides present and if you really want I bet they'd send a copy of
the leach test numbers. If however, they seem evasive or say anything to
the effect of "I just dump mason stains (or anything else) into my glaze
till it turns nice and black" .. well .. I'd not swill wine out their ware
either.
Cheryl Shoemaker
Charleston, SC
Ron Roy on mon 9 mar 98
Just a couple of points on this - I think it is time we begin to questions
our attitudes towards our glazes and our responsibility to those who want
to use handmade pottery to eat from. I deal with hundreds of glazes each
year in my capacity as a clay and glaze consultant. I don't know anyone who
has their glazes tested for durability or leaching. I have never seen the
kind of information with glazes - anywhere - which indicates food safe or
durability. In fact most published glazes are not fit for table or cooking
from the standpoint of durability.
The fact is that many glazes look like they are durable because we have
this idea - looks like glass so it must be OK.
Loss of customer confidence threatens our livelihood - it is right and
proper that we carefully consider the consequences of poorly made ware.
Times have changed - we live in a chemical soup - spotting poorly made
products has become an industry in itself and litigation is common.
This is no less important when we choose glazes that fit the clays we are
working with. In this area we are perfectly capable of doing our own
testing.
We have some pretty abysmal attitudes and poor training to overcome. I
think we should automatically assume the glazes we find - anywhere - are
not fit for table, cooking and storage until some investigation indicates
otherwise.
And I do make black (Tenmoku) dinnerware - the glaze is durable - the
recipe is published - Ceramics Monthly June/July/Aug. 1994.
>----------------------------Original message----------------------------
>>person who leaves coleslaw in a black bowl overnight? Or the person who
>>"always " has a cup fo black coffee in a black cup at her elbow, or a
>>black goblet of red wine beside him as he watches TV all evening.
>>
>>Prevention is much better than cure, Brad; and risk taking is just that.
>
>Lili,
>
>I apologize for not knowing the entirety of this thread, just caught this
>while skimming after return from a road trip and could not let this go.
>
>I agree re: risk taking concerning glazes ... but let's not put everyone
>into a total panic when they see functional ware glazed black. If I had to
>choose between making everybody think it was OK to sloppily concoct black
>glazes and not bother to have them tested OR scare them so bad they'd never
>consider it ... I'd definitely take your message to the masses but it's too
>broad a statement. Let's make it clear that there ARE responsible potters
>out there who use black glaze on functional ware and have it tested every
>time a material changes, firing methods/times change etc. etc.
>
>Want to know if a black glaze is food safe? Have a standard leach test done
>on it at a certified lab for EVERY metal oxide used and any other toxic
>ingredient. It's pretty simple really, put your money where your glaze
>desire is and have it tested ...and tested repeatedly as warranted due to
>material changes, firing changes etc. It's a lot of work but it can be done.
>
>I think the problem lurking on the edge of your statement that may not have
>been addressed is that people seem to want a "recipe" for a black glaze that
>they can call food safe without bothering to have it tested. Therein lies
>the big problem. It's my strong opinion that black glazes are achievable
>for food surfaces if you:
>
>a.) formulate one to your specifications (or find one in a recently
>published book that has the characteristics you want and is supposedly food
>safe)
>b.) do glaze tests to find/use the least toxic metal oxides in the
>smallest percentages possible, read up on glaze safety .. current info
>c.) have a standardized leach test done @ a certified lab before you
>put it on any food surface and keep an eye on the glaze ... The hard part
>is once you get the numbers you may feel you have nothing to compare to,
>where there are no numbers from FDA for dinnerware there are US EPA drinking
>water standards to compare to (these are more stringent numbers to comapre
>to indeed) and you can contact Arts, Crafts & Theater Safety, Inc and/or
>Center for Safety in the Arts for advice too
>d.) keep tight controls on your firings
>e.) have it retested as conditions change.
>
>If you're in someone's booth full of black glazed functional ware and want
>to know if it's safe. ASK them about it. If they are bothering to go thru
>testing etc. they will probably happily tell you about the leach tests done
>and the oxides present and if you really want I bet they'd send a copy of
>the leach test numbers. If however, they seem evasive or say anything to
>the effect of "I just dump mason stains (or anything else) into my glaze
>till it turns nice and black" .. well .. I'd not swill wine out their ware
>either.
Ron Roy
93 Pegasus trail
Scarborough Otario
Canada M1G 3N8
Phone: 416-439-2621
Fax: 416-438-7849
Web page: Home page http://digitalfire.com/education/people/ronroy.htm
pedresel@3-cities.com on sat 14 mar 98
So what is your definition of "durable"? I don't think I'm being snotty to
ask. I looked in several texts including Hammer**2 and only found one
discussion of the term. I'm all or durability in the abstract but think
like most ideals we need to consider what is meant and what is reasonable.
Afterall most pots are not durable when subject to impact from a framing
hammer ;-)
The one discussion I found was in Zakin's Electric Kiln Ceramics:
"Utility and Durability
"Glazes vary greatly in durability. Look for glazes that resist
scratches and abraisions and are free from crazing, bubbling and flaking.
"For glazing utilitarian pieces, look for good durability and easy
cleaning. You may want to use shiny or satin shiny glazes because they are
easier to clean than glazes whose surfaces are mat or dry.
"Many glaze materials that encourage rich character and visual
textures also encourage soft, easily worn surfaces. The desire for a
beautiful surface must be balanced against the need for durability.
Ceramists who create nonutilitarian pieces tend to emphasize the look of the
glaze, while those who create utilitarian pieces or work meant for outdoor
sites will favor durable surfaces."
Not exactly a definition or anything that you can measure but sounds sensible.
-- Evan in W Richland WA where it is quite warm.
At 02:37 PM 3-9-98 EST, you wrote:
>----------------------------Original message----------------------------
>Just a couple of points on this - I think it is time we begin to questions
>our attitudes towards our glazes and our responsibility to those who want
>to use handmade pottery to eat from. I deal with hundreds of glazes each
>year in my capacity as a clay and glaze consultant. I don't know anyone who
>has their glazes tested for durability or leaching. I have never seen the
>kind of information with glazes - anywhere - which indicates food safe or
>durability. In fact most published glazes are not fit for table or cooking
>from the standpoint of durability.
>
>The fact is that many glazes look like they are durable because we have
>this idea - looks like glass so it must be OK.
>
>Loss of customer confidence threatens our livelihood - it is right and
>proper that we carefully consider the consequences of poorly made ware.
>Times have changed - we live in a chemical soup - spotting poorly made
>products has become an industry in itself and litigation is common.
>
>This is no less important when we choose glazes that fit the clays we are
>working with. In this area we are perfectly capable of doing our own
>testing.
>
>We have some pretty abysmal attitudes and poor training to overcome. I
>think we should automatically assume the glazes we find - anywhere - are
>not fit for table, cooking and storage until some investigation indicates
>otherwise.
>
>And I do make black (Tenmoku) dinnerware - the glaze is durable - the
>recipe is published - Ceramics Monthly June/July/Aug. 1994.
>
>
>
>
>
>Ron Roy
>93 Pegasus trail
>Scarborough Otario
>Canada M1G 3N8
>Phone: 416-439-2621
>Fax: 416-438-7849
>Web page: Home page http://digitalfire.com/education/people/ronroy.htm
>
>
Tom Buck on mon 16 mar 98
Evan D raises the question of glaze durability, and states the fact that
the "regular" literature is notoriously deficient in this matter.
To obtain a reasonable view on durability one must go to the texts
written by scientists and engineers who explored glaze technology. Such as
Parmelee, Norton, and Lawrence. Their texts are not easy reading (altho
Lawrence directs his attention to Potters rather than to industrial
ceramicists, and makes a great effort to communicate well).
My favourite author among Potters is Michael Cardew (Pioneer
Pottery). He tackles technical questions from a postion that he needs to
know this data so that he can become more proficient in a rural setting.
So he hit the techie books and interpreted the information in a more
readable manner.
Essentially, one needs the durability of window glass, container
glass, on the surface of one's pots. So if one figures out why these
materials do not melt in the rain, then one is well along to making good
glazes. 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).
Ron Roy on mon 16 mar 98
Hi Evan,
The qoute from Zakin you included I feel is correct - but not much help. I
can say however that most of the glazes in our books, on this list and in
our studios are not balanced and the majority would not pass a durability
test - this is simply because this aspect of pottery has not been a part of
our education - I happen to feel it should be. The world is changing and I
feel there is an advantage in making ware that will do the job of food
containment properly.
I have looked up a few sources and the best place to start is with the
Magic of Fire Book by Tony Hansen - which you can purchase in book form or
download as shareware from the IMC web site - http://digitalfire.com
There is a lot of information you will find interesting - I recommend the
book to anyone who would like to understand the molecular approach to
glazes.
Limit formulas are used in many ways - to assess durability, surface, and
maturing temperature.
There are limit formulas in Zakins book "Mastering the craft" (page
126-127) but they are more about surface quality.
The qoute from Zakin you included I feel is correct - but not much help. I
can say however that most of the glazes in our books, on this list and in
our studios are not balanced and the majority would not pass a durability
test - this is simply because this aspect of pottery has not been a part of
our education - I happen to feel it should be. The world is changing and I
feel there is an advantage in making ware that will do the job of food
containment properly.
The Hamer book has some on page 379 but I don't think they are about durability.
I use two sets - the ones in Magic of Fire and those I got from Glazes for
the Potter by Cooper and Royle - same set in Understanding Pottery Glazes
by David Green. Those are also for assessing durability but with B2O3
included in unity with the fluxes.
After you have read the Magic of Fire sections on Limit Formulas and Safety
(is your fired product safe) I will be happy to answer any questions
(snotty or not) you have - if I can.
I can say - there are many factors involved and limits are not cast in
stone - they do give you some idea about possible durability problems - lab
testing would be the best answer if you insist on using oxides which have
toxicity problems. Durability is much less of a problem if there are no
toxics to leach out - in that case glazes will simply get etched (dulled)
with use.
>----------------------------Original message----------------------------
>So what is your definition of "durable"? I don't think I'm being snotty to
>ask. I looked in several texts including Hammer**2 and only found one
>discussion of the term. I'm all or durability in the abstract but think
>like most ideals we need to consider what is meant and what is reasonable.
>After all most pots are not durable when subject to impact from a framing
>hammer ;-)
>
>The one discussion I found was in Zakin's Electric Kiln Ceramics:
>
>"Utility and Durability
>
> "Glazes vary greatly in durability. Look for glazes that resist
>scratches and abraisions and are free from crazing, bubbling and flaking.
>
> "For glazing utilitarian pieces, look for good durability and easy
>cleaning. You may want to use shiny or satin shiny glazes because they are
>easier to clean than glazes whose surfaces are mat or dry.
>
> "Many glaze materials that encourage rich character and visual
>textures also encourage soft, easily worn surfaces. The desire for a
>beautiful surface must be balanced against the need for durability.
>Ceramists who create nonutilitarian pieces tend to emphasize the look of the
>glaze, while those who create utilitarian pieces or work meant for outdoor
>sites will favor durable surfaces."
>
>Not exactly a definition or anything that you can measure but sounds sensible.
>
>-- Evan in W Richland WA where it is quite warm.
Ron Roy
93 Pegasus trail
Scarborough Otario
Canada M1G 3N8
Phone: 416-439-2621
Fax: 416-438-7849
Web page: Home page http://digitalfire.com/education/people/ronroy.htm
Bill Amsterlaw on wed 18 mar 98
Hi Clayart:
Thinking about durability, the leaching out of toxic substances, liability,
quality control.... These are clearly vital issues to ceramic factories
whose reputations are built on the monotonous sameness of their line of
products. What do these issues mean to me in my own work as a studio
potter?
I have been eating off some shino-glazed plates for many years and the
glaze is beginning to show wear. I like that worn quality. I like the
idea that these plates reveal everything that has occurred to them - marks
left by the hands and tools used in their formation, the way they were
dipped in glaze, the way they were fired, ... and the evidence that they
have been in continuous use for many years. The signs of wear in no way
detract from their utility. In fact, for me, these signs of wear impart
these plates with a kind of dignity that they could not have had when they
were new.
It is important to me that the work itself is durable - but, to me, the
glaze is just clothing. Our clothing covers our bodies; our bodies are
just shells for our spirits. The sweater can have a frayed collar, but it
still warms the wearer, and you can tell whether the wearer is a good
person, whether his sweater is worn or not. A person can acquire wisdom
with age, while the shell that is his body shows progressive signs of age.
It is reassuring to realize that as the glaze ages, the pot is still good;
as I age, I am still good.... Over time, such a pot becomes an old friend
with whom you can associate weighty thoughts and memories of many good
meals.
If the walls of your pots are thick enough and they are fired well, and the
pots are properly cared for, they will be strong enough to last for
centuries ... even if the glaze is crazed. With a vitrified body, you
could use them even if they had no glaze at all.
Surely, I don't want to poison anyone. If you want to decorate the insides
of bowls and platters with toxic substances, then you must seal them in
hard, durable, shiny, uncrazed glass. However, it is possible to have a
reasonably rich palette using substances which are not toxic - in which
case leaching is not an issue. The possibility of leaching from the
outside surfaces of pots which do not come in contact with food, like the
possibility of leaching from sculpture, is not an issue, either.
Financial pressures often influence individual studio potters to do
production work. In the process of putting out volumes of saleable
products and avoiding liability risks, it is easy to become preoccupied
with the concerns of industry and commerce ... and to lose interest in
using the medium to reflect your inner self. But I think that if a soft
surface on functional pottery is part of something you want to say, its ok
to do it as long as you understand what you are doing and the people who
buy your work understand where you are coming from. It is good to know how
to formulate a durable glaze - but our surfaces need not be limited to
durable glazes.
- Bill Amsterlaw (wamster@slic.com)
Plattsburgh, NY
Ron Roy wrote:
<<
....I can say however that most of the glazes in our books, on this list and
in our studios are not balanced and the majority would not pass a
durability test - this is simply because this aspect of pottery has not
been a part of our education - I happen to feel it should be. The world is
changing and I feel there is an advantage in making ware that will do the
job of food containment properly.
....
I can say - there are many factors involved and limits are not cast in
stone - they do give you some idea about possible durability problems - lab
testing would be the best answer if you insist on using oxides which have
toxicity problems. Durability is much less of a problem if there are no
toxics to leach out - in that case glazes will simply get etched (dulled)
with use.
>>
Cindy on thu 19 mar 98
Bill,
Beautiful letter, and I do hate to keep harping on this . . . but I guess I
will anyhow. I agree with your assessment of the beauty of old,
worn-around-the-edges, loved-to-realness things. However, remember what
happened to the velveteen rabbit when he became contaminated with fever
germs. I'm glad the nursery fairy saved him from burning , however
it really would not have done for the boy to have him back.
Glazes which are soft, scratchable, rough, too matte, or even vitrified
surfaces which are not smooth, do harbor microbes. Some may be good
microbes; some will be harmful. Will they make you or your customers sick?
They may--depending on the circumstances. It may be that only a few nasties
remain harbored in a nice, cozy craze line of a platter which has been used
to cut raw meat, washed, and then used to serve the broiled meat. These few
may or may not make you sick, depending on your general state of health.
For myself, I don't like getting sick, so I generally refuse to do so
regardless of the circumstances. Convoluted logic, I suppose, but I don't
mind eating from a crazed platter or drinking from a crazed mug that hasn't
been colored with antimony or fluxed with lead or some such. I would not,
however, be willing to give or sell crazed or soft ware for food use--even
if the customer was aware of the risk.
Cindy Strnad
Earthen Vessels
Custer, SD
USA http://blackhills-info.com/a/cindys/menu.htm
Ron Roy on thu 19 mar 98
The following excerpt from Bills comments on a post of mine about the lack
of integrity of so many of the glazes we use. I found his thoughts
stimulating and a catalyst for expressing some additional aspects of how I
feel about functional glazes.
I respect every ones right to make their own decisions - in fact can do
nothing about them. I often feel I am imposing my own standards - that is
not my intention. I am simply trying to fill in some much needed
information about glazes.
Bills comment about factory glazes is right of course - who wants to do
that? Many potters think that durable glazes must be dull - that is simply
not so. The reason we tend to think that way is because, again, of our
education. Good glass, by definition, has to be ordinary - I don't think
so. I predict we will see, over the next few years, many examples of
durable and interesting glazes which will fulfill our desire for glazes
with character which will also sell well.
The reason we don't have them already is because the empirical method of
developing glazes gives no information about durability and fit. Could it
be that in all those triaxles there was the information to have both - I'll
bet the answer is - sometimes - and in most cases certainly better.
>Thinking about durability, the leaching out of toxic substances, liability,
>quality control.... These are clearly vital issues to ceramic factories
>whose reputations are built on the monotonous sameness of their line of
>products. What do these issues mean to me in my own work as a studio
>potter?
- Bill Amsterlaw (wamster@slic.com)
Plattsburgh, NY
Ron Roy
93 Pegasus trail
Scarborough Otario
Canada M1G 3N8
Phone: 416-439-2621
Fax: 416-438-7849
Web page: Home page http://digitalfire.com/education/people/ronroy.htm
Gavin Stairs on fri 20 mar 98
This business of durability is a bit of a mare's nest. I recall a while
ago (this is one of those anedotal terribles that some members so dislike)
reading about the incidence of pathogens (bad bugs) on (in) food
preparation surfaces which compared wood and plastic cutting boards.
Perhaps anti-intuitively, the wood surfaces won. Apparently there's
something in the wood that the bugs don't like. Score one for ancient,
sainted practice over new, hi-tech whizz-bang.
I don't know if there's any bacteriostatic action in ceramic cracks.
Perhaps in nice, lead-glaze cracks. I have certainly eaten off many
cracked and crazed plates and bowls and am not to my knowledge any the
worse for it. That, I hasten to add, is no evidence for anything. People
ate and drank out of lead pewter for centuries before finally figuring that
one out.
The plates that I use at home are rather ancient English dinnerware plates,
apparently seconds from the look of the printed designs and flaws. They
came from a Quebec farmhouse that was about 200 years old. They show signs
of wear. Scratches, pits, chips, cracks. And yet they are holding up much
better than some more recent plates that show score marks after being
attacked by a stainless steel steak knife or something similar. I also ate
at a restaurant which served me soup in a Chinese trade-ware, handled bowl
which had seen better days. I was charmed, but I think the health
department was not, since the bowls have since disappeared. I am much less
worried about any of these than I am about the crazed surfaces with vibrant
colors that I often see on boutique dinnerware, or the mug that changes
color every time it is used. And I am not at all worried about the same on
bric-a-brac or statuary. I am an advocate for safety testing, and
increasing the general level of understanding of safe practice. I don't
think this obstructs us in making interesting and durable glazes. Rather
the reverse. I'm with Ron Roy on that one.
Where do we draw the line? As an engineer, I incline to the smooth, hard,
tight surface, knowing it to minimize possible problems, and also to
maximize the strength and general durability of the ware. As a craftsman,
I incline to the simple possible. Where these two overlap is simple glazes
made of complex materials, well tested by the methods we have been told of
so often. The prototypes for these qualities are the ash, rock and slip
glazes favored by Hamada and company. Made of few materials, mostly
locally obtained, but very complex in their rheology, chemistry and oxide
formulae.
Today, we tend to make glaze out of purer materials that we purchase from
afar. I'm not saying this is terrible. It just means that we have to
build that same complexity into our glazes by knowledge and intent, rather
than by hallowed practice. Hamada's rice husk straw was rich in silica and
alkalai earths. His volcanic rock was a not very fine powder of mostly
basaltic feldspars. Both complex. Add a bit of local white clay, adjust
with other ashes, and you get a complex formula with difficult slurry
properties which perfectly matches his local clay.
Is this practical for today's studio potter? Apparently not. But Tony
Clennels "50 ash 50 river mud", or even his "80 Alberta 20 nep sy" incline
to that direction. Albany slip is just such a simple complex material, and
Alberta is it's current analog, made out of purer materials. And river mud
is just what it is.
So that is my inclination. As a city dweller, I need to go a piece to find
river mud or rice-husk ash. So I end up with what can be purchased, which
is the purer materials. I think I'll put in an order for a bag of Alberta.
Anybody know where to buy rice-husk ash?
Gavin
Bill Amsterlaw on fri 20 mar 98
Hi Clayart:
Cindy Strnad wrote:
<<
Glazes which are soft, scratchable, rough, too matte, or even vitrified
surfaces which are not smooth, do harbor microbes. Some may be good
microbes; some will be harmful. Will they make you or your customers sick?
.... I would not ... be willing to give or sell crazed or soft ware for food
use--even if the customer was aware of the risk.
>>
Living with microbes is part of life. They exist on practically every
surface and in the air we breathe. Every organism has evolved defenses to
deal with this reality. The risk of becoming infected by eating from a
clean plate whose glazed surface is slightly worn or crazed is no greater
than the risk of eating from a shiny, factory-fresh plate; in either case,
the risk is nil.
A << soft >> glaze is soft like a rock. Some rocks are harder than others;
everything wears down with age. I am not suggesting we clothe pots in
crumbly stuff that you can readily scratch. I am talking about rock-hard
surfaces that may show signs of wear a little sooner than other rock-hard
surfaces.
Things made of well-fired clay tend to be durable, no matter how they are
glazed. The long view: Will this pot still be good in 30 years or more?
The study of glaze chemistry makes it possible to predict how durable a
given glaze might be. My choice of glaze will be an aesthetic decision,
with an understanding of the durability of the glaze and the long view in
mind - but I don't feel compelled to limit my choices to the hardest
possible surfaces.
- Bill Amsterlaw (wamster@slic.com)
Plattsburgh, NY
Original message:
<<<
----------
Date: Tue, March 17, 1998
From: Bill Amsterlaw
Subj: Re: food safe black glaze ... wait a minute
Hi Clayart:
Thinking about durability, the leaching out of toxic substances, liability,
quality control.... These are clearly vital issues to ceramic factories
whose reputations are built on the monotonous sameness of their line of
products. What do these issues mean to me in my own work as a studio
potter?
I have been eating off some shino-glazed plates for many years and the
glaze is beginning to show wear. I like that worn quality. I like the
idea that these plates reveal everything that has occurred to them - marks
left by the hands and tools used in their formation, the way they were
dipped in glaze, the way they were fired, ... and the evidence that they
have been in continuous use for many years. The signs of wear in no way
detract from their utility. In fact, for me, these signs of wear impart to
these plates a kind of dignity that they could not have had when they were
new.
It is important to me that the work itself is durable - but, to me, the
glaze is just clothing. Our clothing covers our bodies; our bodies are
just shells for our spirits. The sweater can have a frayed collar, but it
still warms the wearer, and you can tell whether the wearer is a good
person, whether his sweater is worn or not. A person can acquire wisdom
with age, while the shell that is his body shows progressive signs of age.
It is reassuring to realize that as the glaze ages, the pot is still good;
as I age, I am still good.... Over time, such a pot becomes an old friend
with whom you can associate weighty thoughts and memories of many good
meals.
If the walls of your pots are thick enough and they are fired well, and the
pots are properly cared for, they will be strong enough to last for
centuries ... even if the glaze is crazed. With a vitrified body, you
could use them even if they had no glaze at all.
Surely, I don't want to poison anyone. If you want to decorate the insides
of bowls and platters with toxic substances, then you must seal them in
hard, durable, shiny, uncrazed glass. However, it is possible to have a
reasonably rich palette using substances which are not toxic - in which
case leaching is not an issue. The possibility of leaching from the
outside surfaces of pots which do not come in contact with food, like the
possibility of leaching from sculpture, is not an issue, either.
Financial pressures often influence individual studio potters to do
production work. In the process of putting out volumes of saleable
products and avoiding liability risks, it is easy to become preoccupied
with the concerns of industry and commerce ... and to lose interest in
using the medium to reflect your inner self. But I think that if a soft
surface on functional pottery is part of something you want to say, its ok
to do it as long as you understand what you are doing and the people who
buy your work understand where you are coming from. It is good to know how
to formulate a durable glaze - but our surfaces need not be limited to
durable glazes.
- Bill Amsterlaw (wamster@slic.com)
Plattsburgh, NY
Ron Roy wrote:
<<
....I can say however that most of the glazes in our books, on this list and
in our studios are not balanced and the majority would not pass a
durability test - this is simply because this aspect of pottery has not
been a part of our education - I happen to feel it should be. The world is
changing and I feel there is an advantage in making ware that will do the
job of food containment properly.
....
I can say - there are many factors involved and limits are not cast in
stone - they do give you some idea about possible durability problems - lab
testing would be the best answer if you insist on using oxides which have
toxicity problems. Durability is much less of a problem if there are no
toxics to leach out - in that case glazes will simply get etched (dulled)
with use.
>>
>>>
Cindy on sat 21 mar 98
Bill,
Neither do I feel compelled to limit my choices to the hardest possible
surfaces. But I will not sell a glaze which crazes at all or scratches
easily. Eating from a polished stone and eating from a slab of granite are
two entirely different things. Both are rock. One can be cleaned without a
great deal of trouble, the other cannot. This is an overstatement of the
issue, I understand, simply to make a point.
If you want to take the risk of eating from scratched and crazed surfaces,
that is your decision. I suppose if you wish to sell easily scratched or
crazed dinnerware, that's your decision, too. For me, it's a matter of
ethics. People can and do get sick eating contaminated food, and unclean
tableware can contaminate foods--especially liquid or soft foods. Yes, the
risk of getting food poisoning from eating from a clean plate is nil. You
are absolutely right, Bill. The point is that crazed, scratched, chipped
plates are difficult to clean. To really clean them, you'll have to put
them in your kiln, not your sink.
Cindy Strnad
Earthen Vessels
Custer, SD
USA http://blackhills-info.com/a/cindys/menu.htm
Tony Hansen on sun 22 mar 98
> It is good to know how
> to formulate a durable glaze - but our surfaces need not be limited to
> durable glazes.
As long as our customers know that also.
If a crazed vessel is one quarter the strength of a fitted one the
customer
should have some idea that this amount of strength is being sacrificed
for visual character so that he can make an informed choice.
Crazed pots are generally looking for the earliest opportunity to chip,
crack, and shatter.
--
-------
T o n y H a n s e n thansen@digitalfire.com
Get INSIGHT, Magic of Fire at http://digitalfire.com
| |
|
