wqwilcox@my-dejanews.com on tue 18 aug 98
I am trying to find out if anyone out there has a definitive answer to
whether lead glazes are safe. The research I've done says basically that if
lead glazes are fired hot enough, and assuming that there is not too much
lead present, that the lead goes into solution with the silica and once fired
like this, lead will not leach out. One of the people in my studio is saying
that no matter what you do, lead can leach out when in contact with mild
acids, like tomatoes. In addition I have heard that some American dinnerware
companies use lead and don't have problems when properly fired. Does anyone
have a definitive answer? Thanks Bill
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Gavin Stairs on wed 19 aug 98
At 10:44 AM 8/18/98 EDT, Bill wrote:
>... Does anyone have a definitive answer? Thanks Bill
Dear Bill:
I guess you haven't been following the glaze safety discussion on this list
very closely. If you had, you would have heard, over and over again, that
there is no such thing as a definitive answer. The only answer is test,
test, test. You would also have read about the consequential dangers of
using lead glazes; of lead fuming, of lead contamination of kilns which
fire lead glazes. And you would have heard that very few people on this
list and elsewhere consider lead glazes suitable for foodware anymore; that
one exposes oneself to federal regulatory disapproval in the US and Canada,
among other countries; and that lead glazes are perhaps most harmful to the
potters who use them.
Trisilicate lead frits were supposed to be the answer to lead leaching and
body absorbtion. Subsequent testing has revealed that this is not the
case: lead may still be leached from the glaze and absorbed by the body.
The rate at which this occurs is dependant upon many factors relating to
glaze durability and resistance to chemical attack.
The major reasons that most responsible potters who make foodware should
not use any lead glaze are:
1. Lead glazes fume, exposing the potter to kiln fumes, and contaminating
the kiln and other ware in the kiln, both during a lead glaze firing, and
during subsequent firings, whether or not they include lead glazes. In
particular, even if a lead free liner glaze is used, it may be contaminated
with fumed lead from other pots or from the kiln or from kiln furniture.
2. Lead frits and lead glazes introduce poisonous powders into the work
area which it would be better to avoid. Having lead in the studio exposes
one to the risk of contamination of other materials and accidental release
(spills and errors). Better to have none at all.
3. Lead is environmentally unfriendly, and makes for disposal problems in
water and residues.
4. There are alternatives to the use of lead. It is true that certain
lead glazes are hard to reproduce, but this is less true now that
encapsulated colorants are available.
5. There are stringent regulations concerning the use, release and
labeling of lead in pottery and glazes. Consumers are also sensitive to
the release of lead from ware, and, if informed as is their right, may
choose not to buy leaded ware.
6. Lead leaching release testing is expensive, costing in the region of
hundreds of dollars per test. The US tests are prescribed by the FDA.
7. Lead glaze materials are definitely not safe for use by students,
particularly young ones.
Notwithstanding all of the above, some potters continue to use lead,
particularly for sculptural and non-functional work. I would not buy food
ware from any of these potters, for the reasons cited above. It also seems
to be true that the foodware industry is still somewhat addicted to lead.
Some firms choose lead in their production wares because it allows them to
make (otherwise) problem free glazes, at the cost of constant risk of
regulatory sanctions should their ware be found to release lead above the
regulation limits.
Hope this approaches an answer to your question.
Gavin
Karen Gringhuis on wed 19 aug 98
Dear Bill - NO, you can NOT extrapolate lead glaze safety from
ANYTHING done in industry. Beleive me they have much stricter
more reliable firing controls than you or I want to know.
Lead also releases hazardous fumes in firing (no tomatoes needed)
which YOU can breathe - just one of the ways it's hazardous.
If you are using it on functional work, PLEASE go find the article
in Ceramics Monthly written by Val Cushing (one of the ranking glaze
experts in the WORLD) circa 1993 titled "Get the Lead Out" - get
busy and develop some new LEAD-FREE glazes. Karen Gringhuis
Tony Hansen on thu 20 aug 98
> I am trying to find out if anyone out there has a definitive answer to
> whether lead glazes are safe. The research I've done says basically that if
> lead glazes are fired hot enough, and assuming that there is not too much
> lead present, that the lead goes into solution with the silica and once fired
> like this, lead will not leach out.
I'd be very careful. The composition matters more than the firing.
You need test equipment and to know what you are doing. You need to
know about the chemistry issues. Lead products
are not safe to work with without the proper ventilation and material
handling equipment.
--
T o n y H a n s e n thansen@digitalfire.com
Don't fight the dragon alone http://digitalfire.com
Calculation/Database Software for Ceramic Industry
Barbara Lewis on thu 20 aug 98
The other thing that hasn't been mentioned, but I think Monona Rossol can
confirm, when Duncan/Mayco lead glazes were recently tested, they showed
higher concentrations of lead than was stated on the label or in their
literature. Barbara
At 09:31 AM 8/19/98 EDT, you wrote:
>----------------------------Original message----------------------------
>At 10:44 AM 8/18/98 EDT, Bill wrote:
>>... Does anyone have a definitive answer? Thanks Bill
>
>Dear Bill:
>
>I guess you haven't been following the glaze safety discussion on this list
>very closely. If you had, you would have heard, over and over again, that
>there is no such thing as a definitive answer. The only answer is test,
>test, test. You would also have read about the consequential dangers of
>using lead glazes; of lead fuming, of lead contamination of kilns which
>fire lead glazes. And you would have heard that very few people on this
>list and elsewhere consider lead glazes suitable for foodware anymore; that
>one exposes oneself to federal regulatory disapproval in the US and Canada,
>among other countries; and that lead glazes are perhaps most harmful to the
>potters who use them.
>
>Trisilicate lead frits were supposed to be the answer to lead leaching and
>body absorbtion. Subsequent testing has revealed that this is not the
>case: lead may still be leached from the glaze and absorbed by the body.
>The rate at which this occurs is dependant upon many factors relating to
>glaze durability and resistance to chemical attack.
>
>The major reasons that most responsible potters who make foodware should
>not use any lead glaze are:
>
>1. Lead glazes fume, exposing the potter to kiln fumes, and contaminating
>the kiln and other ware in the kiln, both during a lead glaze firing, and
>during subsequent firings, whether or not they include lead glazes. In
>particular, even if a lead free liner glaze is used, it may be contaminated
>with fumed lead from other pots or from the kiln or from kiln furniture.
>
>2. Lead frits and lead glazes introduce poisonous powders into the work
>area which it would be better to avoid. Having lead in the studio exposes
>one to the risk of contamination of other materials and accidental release
>(spills and errors). Better to have none at all.
>
>3. Lead is environmentally unfriendly, and makes for disposal problems in
>water and residues.
>
>4. There are alternatives to the use of lead. It is true that certain
>lead glazes are hard to reproduce, but this is less true now that
>encapsulated colorants are available.
>
>5. There are stringent regulations concerning the use, release and
>labeling of lead in pottery and glazes. Consumers are also sensitive to
>the release of lead from ware, and, if informed as is their right, may
>choose not to buy leaded ware.
>
>6. Lead leaching release testing is expensive, costing in the region of
>hundreds of dollars per test. The US tests are prescribed by the FDA.
>
>7. Lead glaze materials are definitely not safe for use by students,
>particularly young ones.
>
>Notwithstanding all of the above, some potters continue to use lead,
>particularly for sculptural and non-functional work. I would not buy food
>ware from any of these potters, for the reasons cited above. It also seems
>to be true that the foodware industry is still somewhat addicted to lead.
>Some firms choose lead in their production wares because it allows them to
>make (otherwise) problem free glazes, at the cost of constant risk of
>regulatory sanctions should their ware be found to release lead above the
>regulation limits.
>
>Hope this approaches an answer to your question.
>
>Gavin
>
Wellspring Clayworks
5412 Well Spring Road
La Plata, MD 20646
blewis@crosslink.net
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