Numo Jaeger & Michael Miller on mon 18 oct 99
If a glaze leaches a metal above drinking water levels will it still leach
the metal if a clear glaze is layered on the top before firing?
Does anyone know the answer to this question. Or do I need to have the
glaze tested with a clear glaze over the top?
Numo
Numo Jaeger
Studio One Art Center
Oakland CA
Craig Martell on tue 19 oct 99
Numo asked:
>If a glaze leaches a metal above drinking water levels will it still leach
>the metal if a clear glaze is layered on the top before firing?
Hi:
John Hesselberth posted some info on this a while back. He applied a clear
glaze over another glaze that was leaching a bit too much metal and found
that this improved things quite a bit. In fact, I believe he said that the
glaze with an overglaze of clear was then within accepted limits. I think
that you will still want to test though.
regards, Craig Martell in Oregon
John Hesselberth on tue 19 oct 99
Numo Jaeger & Michael Miller wrote:
>----------------------------Original message----------------------------
>If a glaze leaches a metal above drinking water levels will it still leach
>the metal if a clear glaze is layered on the top before firing?
>
>Does anyone know the answer to this question. Or do I need to have the
>glaze tested with a clear glaze over the top?
>
>Numo
>
>Numo Jaeger
>Studio One Art Center
>Oakland CA
Hi Numo,
In one test, that you can find in the archives, I saw a nearly 10 fold
decrease in leaching by putting a thin coat of a clear glaze on top of a
copper-containing glaze. So it CAN work, at least under certain
circumstances. Whether or not it will work in your case depends on the
specific glazes you are using and how much intermingling of those glazes
occurs during firing. You must test to get an answer to this question
with our current state of knowledge. Please do that and report your
results back to the group. We are all trying to learn together in this
area and each of us can contribute a little bit to our knowledge.
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"It is time for potters to claim their proper field. Pottery in its pure
form relies neither on sculptural additions nor on pictorial decorations.
but on the counterpoint of form, design, colour, texture and the quality
of the material, all directed to a function." Michael Cardew in "Pioneer
Pottery"
Ron Roy on tue 19 oct 99
John Hesselberth will answer this because he has done it.
I am sure one could mess this approach up if the over glaze was bad enough
- would be an interesting experiment.
I was down at the Roland Hales lab in Alfred last week - good guy - pots
all over the place. What a bargain it is - getting ware tested for leachate
for $20 - we all better get our glazes tested while he is still doing it
for that price.
Leaching with vinegar is $10
Analyze for each element $10 (each)
All you need to do is send him a cup with the glaze on the inside - and if
you really want to contribute to the results of this - send him the recipe
of the glaze and tell him he can use the information in his data base.
We will be much better able to judge durability when this project is done
and the more samples included the more reliable the data will be.
RR
>----------------------------Original message----------------------------
>If a glaze leaches a metal above drinking water levels will it still leach
>the metal if a clear glaze is layered on the top before firing?
>
>Does anyone know the answer to this question. Or do I need to have the
>glaze tested with a clear glaze over the top?
>
>Numo
>
>Numo Jaeger
>Studio One Art Center
>Oakland CA
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
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