PJLewing@aol.com on sun 16 mar 97
A friend of mine asked me to post his problem to all you clay detectives out
there.
He makes sinks at ^04 oxidation and wants them to be really white white.
Lately he has been getting specks that he's sure are copper- black with
green halos, about 1/16" diameter. There are usually no more than one or two
in a sink, and not in every one. Just enough to drive him crazy. He
slip-casts the sinks, and on some sprays on a white engobe, bisques, and
sprays on a white glaze. Some of the glazes he makes himself, others are
commercial, and come wet. He has recently moved his shop, and this has
happened in both shops, with water from three different water systems.
He has put a filter on his air tank and one on his spray gun. He always puts
shelves over all his sinks in the kiln, even when they are on the top, but
never puts a shelf closer than 3" above a sink. He only glazes the inside of
these sinks. This has happened in two different kilns, and it doesn't seem
to matter whether the sink is on the top or bottom of the kiln. He ball
mills all the glazes. He has cleaned out his spray booth, and his new studio
has very little dust in it.
There is no evidence of the spots on greenware or bisque.
Any ideas?
Paul Lewing, Seattle, where today's rain is almost cold enough to be snow.
Tomorrow's rain is forecast to be a bit warmer.
Emily Pearlman on mon 17 mar 97
>----------------------------Original message----------------------------
>A friend of mine asked me to post his problem to all you clay detectives out
>there.
>He makes sinks at ^04 oxidation and wants them to be really white white.
> Lately he has been getting specks that he's sure are copper- black with
>green halos, about 1/16" diameter. There are usually no more than one or two
>in a sink, and not in every one. Just enough to drive him crazy. He
>slip-casts the sinks, and on some sprays on a white engobe, bisques, and
>sprays on a white glaze. Some of the glazes he makes himself, others are
>commercial, and come wet. He has recently moved his shop, and this has
>happened in both shops, with water from three different water systems.
>He has put a filter on his air tank and one on his spray gun. He always puts
>shelves over all his sinks in the kiln, even when they are on the top, but
>never puts a shelf closer than 3" above a sink. He only glazes the inside of
>these sinks. This has happened in two different kilns, and it doesn't seem
>to matter whether the sink is on the top or bottom of the kiln. He ball
>mills all the glazes. He has cleaned out his spray booth, and his new studio
>has very little dust in it.
>There is no evidence of the spots on greenware or bisque.
>
>Any ideas?
>Paul Lewing, Seattle, where today's rain is almost cold enough to be snow.
> Tomorrow's rain is forecast to be a bit warmer.
Hi: I had the same problem a while back at cone 6. At that time I was
using a stoneware clay with grog from Standard Clay. After may discussions
with Julie at Standard and sending her some samples of my pots with the
green spots, she came up with the idea that it was contaminated grog in
the clay. She said that while they were careful sometimes some got in.
She suggested that I switch bodies to the same one without grog in it. It
has fireclay in it to repace the grog. The new clay works as well for me
and the green spots are gone.
Emily
Emily Pearlman-Pottery (clayfeat@echonyc.com)
http://humanarts.com/emilypearlman
http://www.craftweb.com/org/pearlman/pearlman.htm
(in NYC)
Hertz Pottery on mon 17 mar 97
You didnt mention the clay he used and more important the ingredients in the
clay...
I use "standard 306" and it has the same copper spots you mention. not very
often but they show-up on otherwise first quality pots. it also has , or
used to have, chunks about 1-2 mm in size that show up in almost every
piece. when i asked about the copper, I had also seen what I think is Iron
chunks, they assured me the recipe had changed and I wouldnt see it in the
new batch of clay. and i have to admit it has become very much less frequent..
I wonder if its backing up in my pugmill screen?
Erik
>----------------------------Original message----------------------------
>A friend of mine asked me to post his problem to all you clay detectives out
>there.
>He makes sinks at ^04 oxidation and wants them to be really white white.
> Lately he has been getting specks that he's sure are copper- black with
>green halos, about 1/16" diameter. There are usually no more than one or two
>in a sink, and not in every one. Just enough to drive him crazy. He
>slip-casts the sinks, and on some sprays on a white engobe, bisques, and
>sprays on a white glaze. Some of the glazes he makes himself, others are
>commercial, and come wet. He has recently moved his shop, and this has
>happened in both shops, with water from three different water systems.
>He has put a filter on his air tank and one on his spray gun. He always puts
>shelves over all his sinks in the kiln, even when they are on the top, but
>never puts a shelf closer than 3" above a sink. He only glazes the inside of
>these sinks. This has happened in two different kilns, and it doesn't seem
>to matter whether the sink is on the top or bottom of the kiln. He ball
>mills all the glazes. He has cleaned out his spray booth, and his new studio
>has very little dust in it.
>There is no evidence of the spots on greenware or bisque.
>
>Any ideas?
>Paul Lewing, Seattle, where today's rain is almost cold enough to be snow.
> Tomorrow's rain is forecast to be a bit warmer.
>
>
erik hertz
gshaffer on tue 18 mar 97
Hertz Pottery wrote:
>
> ----------------------------Original message----------------------------
> You didnt mention the clay he used and more important the ingredients in the
> clay...
> I use "standard 306" and it has the same copper spots you mention. not very
> often but they show-up on otherwise first quality pots. it also has , or
> used to have, chunks about 1-2 mm in size that show up in almost every
> piece. when i asked about the copper, I had also seen what I think is Iron
> chunks, they assured me the recipe had changed and I wouldnt see it in the
> new batch of clay. and i have to admit it has become very much less frequent..
> I wonder if its backing up in my pugmill screen?
> Erik
> >----------------------------Original message----------------------------
> >A friend of mine asked me to post his problem to all you clay detectives out
> >there.
> >He makes sinks at ^04 oxidation and wants them to be really white white.
> > Lately he has been getting specks that he's sure are copper- black with
> >green halos, about 1/16" diameter. There are usually no more than one or two
> >in a sink, and not in every one. Just enough to drive him crazy. He
> >slip-casts the sinks, and on some sprays on a white engobe, bisques, and
> >sprays on a white glaze. Some of the glazes he makes himself, others are
> >commercial, and come wet. He has recently moved his shop, and this has
> >happened in both shops, with water from three different water systems.
> >He has put a filter on his air tank and one on his spray gun. He always puts
> >shelves over all his sinks in the kiln, even when they are on the top, but
> >never puts a shelf closer than 3" above a sink. He only glazes the inside of
> >these sinks. This has happened in two different kilns, and it doesn't seem
> >to matter whether the sink is on the top or bottom of the kiln. He ball
> >mills all the glazes. He has cleaned out his spray booth, and his new studio
> >has very little dust in it.
> >There is no evidence of the spots on greenware or bisque.
> >
> >Any ideas?
> >Paul Lewing, Seattle, where today's rain is almost cold enough to be snow.
> > Tomorrow's rain is forecast to be a bit warmer.
> >
> >
> erik hertz
hello folks with copper spots,
standard ceramics used to buy their grog from maryland refractories
who grind up old bricks to make grog. they ground some bricks from a
bronze smelting plant and sent the grog to standard and it made copper
spots on pots. standard has since changed to hw grog and no longer has
that problem. good luck
gary shaffer
gshaffer@weir.net
Gavin Stairs on tue 18 mar 97
At 09:28 AM 17/03/97 EST, Paul Lewing wrote:
....
>> Lately he has been getting specks that he's sure are copper- black with
>>green halos, about 1/16" diameter. ...
This is beautiful. It shows the diffusion of a metallic salt or oxide in
the glaze, and quantifies it rather neatly. This is the basic transport
process that underlies glaze formation from particles of a mixture. I have
an idea that this might be used to design a neat analytic or testing technique.
Thanks! Gavin
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