John Baymore on sun 27 jun 99
------------------
(snip)
As far as COBALT LEACHING in a glaze I wouldnt worry about it as
it will just go through the system with that bran muffin. If you have
cobalt
leaching from your glaze that means that your glaze is probably not quite
stable to begin with as cobalt is the dream colorant that distributes
itself
well throughout the glaze and gives strong color in minute amounts without
changing the overall nature of the glaze not to mention the fact that that
it provides reliable color seldom affected in just about all conditions
whether chemical, thermal, or atmosphere of the kiln. If the glaze can
leach
cobalt it is probably not a stable enough glaze to be used as a food grade
surface and would probably scratch easily with a steak knife.
(clip)
Tim,
Interesting...... wonder what E.B. Md. and Monona will have to say to the
documentation in your last post?
=22......... glaze is probably not stable to begin with.........=22
This is where the REAL issue lies here. There's a lot of glazes out there
scratching with a steak knife.
Those who are newer to ceramics here please forgive me ..... we all have to
learn somewhere, and I don't mean this to sound harsh...... but there are a
lot of people making ceramic glazes and sticking them on functional pottery
(and selling them or giving them away) that have very little understanding
of what is happening when they are playing with their big chemistry set.
Even many of those in the college level education programs are not getting
too much technical education.
We can go to the ceramic supplier and but most anything, we can weigh it
out in any proportion we want, and we can stick it on a pot. If it looks
good...... we call it a nice glaze. End of story. No testing other than
an eyeball.....and probably without even a loupe either. I'd say that
many, if not most, people doing clay don't even know that they should be
concerned about issues like durability and leaching in functional glazes,
or what things might affect those properties. It isn't being taught.
If you analize the =22glazes=22 in use in the studio pottery world, you'll =
find
that a huge proportion of them are less than optimal when it comes to
durability and hardness and an even somewhat balanced molecular formula.
One need merely to monitor the glazes and the questions here on CLAYART to
realize that there is not a lot of deep technical background in the field,
and few resources (a big Yea for Ron Roy, Tony Hansen, Tom Buck, Paul
Lewing, Richard Burkett and a few others for helping). Another example,
in the Columbus Glaze Doctor session, Dr. Eppler was really talking pretty
basic, basic, basic stuff....... but it was WAY over the heads of a an
awful lot of people in the room (thank god Jonathan was there to translate
a bunch of it to =22potter-speak=22).
So Tim, if you are acknowledging that there IS a little concern about
cobalt toxicity...... but we shouldn't worry because if it IS leaching, it
is simply a glaze problem........ which of course you'd
correct.............you NEED to take into account the audience to whom you
are writing ....or maybe I should better say ......who are reading your
writing. Along the lines I have said before, say.... take a guy like
......oh..............maybe Tom Buck. Tom can probably develop and handle
serious stuff like raw lead glazes with his vast chemical background.......
but simply because HE could do it would not be the case for recommending
that it come broadly into general practice without some serious caveats.
Cobalt is pretty safe if you know what you are doing with it and you have
safeguards in place. So is a loaded gun. Anyone who has Tom Buck's kind
of background...... feel secure that you probably can handle cobalt safely
and make wares that are not a unacceptable hazard to the users. For the
rest of us........... please check carefully to see if there is one in the
chamber before you assume that =22the gun=22 is not loaded =3Cg=3E. And =
leave the
trigger lock on. And still treat it with some respect.
As to the Toxicity Top 10 list.......... I too think cobalt is a ways down
the scale when you look at =22common studio practice=22. That doesn't make =
it
innocious (sp?). Heck.... we still have studio clayworkers here in the US
with little technical expertise or controls using lead glazes. Puts cobalt
compounds a bit down the =22major prime concerns=22 list =3Cwg=3E.
BEst,
..................john
=22Not a big fan of witch hunts....... just trying to keep within the bounds
of reality.=22
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752
JBaymore=40compuserve.com
John.Baymore=40GSD-CO.COM
=22Earth, Water, and Fire climbing kiln firing workshop Aug. 20-29,1999=22
John Baymore on sun 27 jun 99
------------------
(snip)
As far as COBALT LEACHING in a glaze I wouldnt worry about it as
it will just go through the system with that bran muffin. If you have
cobalt
leaching from your glaze that means that your glaze is probably not quite
stable to begin with as cobalt is the dream colorant that distributes
itself
well throughout the glaze and gives strong color in minute amounts without
changing the overall nature of the glaze not to mention the fact that that
it provides reliable color seldom affected in just about all conditions
whether chemical, thermal, or atmosphere of the kiln. If the glaze can
leach
cobalt it is probably not a stable enough glaze to be used as a food grade
surface and would probably scratch easily with a steak knife.
(clip)
Tim,
Interesting...... wonder what E.B. Md. and Monona will have to say to the
documentation in your last post?
=22......... glaze is probably not stable to begin with.........=22
This is where the REAL issue lies here. There's a lot of glazes out there
scratching with a steak knife.
Those who are newer to ceramics here please forgive me ..... we all have to
learn somewhere, and I don't mean this to sound harsh...... but there are a
lot of people making ceramic glazes and sticking them on functional pottery
(and selling them or giving them away) that have very little understanding
of what is happening when they are playing with their big chemistry set.
Even many of those in the college level education programs are not getting
too much technical education.
We can go to the ceramic supplier and but most anything, we can weigh it
out in any proportion we want, and we can stick it on a pot. If it looks
good...... we call it a nice glaze. End of story. No testing other than
an eyeball.....and probably without even a loupe either. I'd say that
many, if not most, people doing clay don't even know that they should be
concerned about issues like durability and leaching in functional glazes,
or what things might affect those properties. It isn't being taught.
If you analize the =22glazes=22 in use in the studio pottery world, you'll =
find
that a huge proportion of them are less than optimal when it comes to
durability and hardness and an even somewhat balanced molecular formula.
One need merely to monitor the glazes and the questions here on CLAYART to
realize that there is not a lot of deep technical background in the field,
and few resources (a big Yea for Ron Roy, Tony Hansen, Tom Buck, Paul
Lewing, Richard Burkett and a few others for helping). Another example,
in the Columbus Glaze Doctor session, Dr. Eppler was really talking pretty
basic, basic, basic stuff....... but it was WAY over the heads of a an
awful lot of people in the room (thank god Jonathan was there to translate
a bunch of it to =22potter-speak=22).
So Tim, if you are acknowledging that there IS a little concern about
cobalt toxicity...... but we shouldn't worry because if it IS leaching, it
is simply a glaze problem........ which of course you'd
correct.............you NEED to take into account the audience to whom you
are writing ....or maybe I should better say ......who are reading your
writing. Along the lines I have said before, say.... take a guy like
......oh..............maybe Tom Buck. Tom can probably develop and handle
serious stuff like raw lead glazes with his vast chemical background.......
but simply because HE could do it would not be the case for recommending
that it come broadly into general practice without some serious caveats.
Cobalt is pretty safe if you know what you are doing with it and you have
safeguards in place. So is a loaded gun. Anyone who has Tom Buck's kind
of background...... feel secure that you probably can handle cobalt safely
and make wares that are not a unacceptable hazard to the users. For the
rest of us........... please check carefully to see if there is one in the
chamber before you assume that =22the gun=22 is not loaded =3Cg=3E. And =
leave the
trigger lock on. And still treat it with some respect.
As to the Toxicity Top 10 list.......... I too think cobalt is a ways down
the scale when you look at =22common studio practice=22. That doesn't make =
it
innocious (sp?). Heck.... we still have studio clayworkers here in the US
with little technical expertise or controls using lead glazes. Puts cobalt
compounds a bit down the =22major prime concerns=22 list =3Cwg=3E.
BEst,
..................john
=22Not a big fan of witch hunts....... just trying to keep within the bounds
of reality.=22
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752
JBaymore=40compuserve.com
John.Baymore=40GSD-CO.COM
=22Earth, Water, and Fire climbing kiln firing workshop Aug. 20-29,1999=22
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