David & Diane Chen on tue 27 apr 99
I first learned about pottery at a local pottery that is fairly well known =
in
this state. When I decided I could wreck pottery on my own and didn't need =
them
to help me I ordered a fair amount of raw materials in order to mix some =
glazes.
Now, one year later, I am realizing a few things:
1. The local pottery used to mix glazes in the same room as the 10 =
students.
No one ever put a mask on. I took classes there for several years, there =
were
very little safety measures. They kept the place very clean, but on many
occasions almost burned the place down when the wax burning on the hot plate=
was
left unattended and started smoking uncontrollably. I have seen them =
dumping
raw materials into buckets with the lighter materials floating up into the
air--again, no masks.
2. They claimed all their glazes are food safe which I highly doubt. =
They
used alot of cobalt, and they had a very successful lt blue matte glaze that
people loved. Their most successful glazes had lots of blue and green =
although
they kept recipes kind of a secret. Maybe it is possible to have that wide =
a
range of blues and be food safe?
3. Now that I have all these (in some instances, dangerous) raw =
materials, I
am wondering how to incorporate some of these questionable test glazes into
safer results.
4. I am begging my friend not to eat off her lusterware cake plates that =
she
got at that yard sale=21
This is probably a very stupid question, but if I have a dangerous glaze =
with
say alot of barium, can I reglaze with a safe transparent glaze? I read
somewhere that the safest way to get color is to use underglazes and then a
transparent overglaze. Why wouldn't this work with regular glazes?
Diane
John Hesselberth on wed 28 apr 99
Hi Diane,
It's great to see that you want to learn more about how to safely handle
and use your glaze materials. Unfortunately, there are no simple answers
to the questions you ask. The only way to really learn what you are
doing is to have your glazes tested at a place like Alfred Analytical Lab
(for instructions on how to do this, go to
http://www.frogpondpottery.com/glazetest.html).
I have, though, had success with one glaze by over coating it with a thin
coating of a transparent glaze. I was able to cut down the leaching by a
factor of about 10. This is two experiments with one glaze. That
doesn't say anything about how that technique will work with other glaze
formulations or firing conditions. I did this in a single glaze firing.
I haven't a clue how this would work to "rescue" a previously fired glaze.
Your specific worry about cobalt may or may not be valid. Since cobalt
give intense blues at a very low levels and seems to be relatively easy
to keep in a glaze, it may not be a problem. Again, though, the only way
to know is to have your glazes tested. Copper is more difficult to keep
in a glaze in general so the green glazes you are wondering about may be
higher leaching (of course if the green came from chrome that could also
be a problem)
I don't use barium and have never tested a barium-containing glaze.
However if you are just starting to formulate glazes why would you want
to use it? There are a lot of attractive glazes to be explored without
resorting to barium. Some people get barium-like effects with strontium
instead.
My recommendation to you and all others who are relatively new to
formulating their own glazes is to stick with the least toxic materials
you can. When you understand the chemistry better, then, if you feel you
must, you might experiment with some of the other materials. I consider
myself to be fairly knowledgeable about glaze chemistry, but I still
don't use lead, barium, nickel or chrome in my glazes. I work hard to
minimize leaching of copper, cobalt and manganese. Iron I don't worry
much about; although I have tested for it on a couple occasions to give
me a general indication of glaze stability.
Ultimately, you have to define your own approach and standards because
there are not regulations or laws that will define it for you; however
you are off to a good start just by raising and considering the issue
before you get too far into it.
John
David & Diane Chen wrote:
>----------------------------Original message----------------------------
>I first learned about pottery at a local pottery that is fairly well known in
>this state. When I decided I could wreck pottery on my own and didn't
>need them
>to help me I ordered a fair amount of raw materials in order to mix some
>glazes.
>Now, one year later, I am realizing a few things:
>
>1. The local pottery used to mix glazes in the same room as the 10
>students.
>No one ever put a mask on. I took classes there for several years, there
>were
>very little safety measures. They kept the place very clean, but on many
>occasions almost burned the place down when the wax burning on the hot
>plate was
>left unattended and started smoking uncontrollably. I have seen them dumping
>raw materials into buckets with the lighter materials floating up into the
>air--again, no masks.
>
>2. They claimed all their glazes are food safe which I highly doubt. They
>used alot of cobalt, and they had a very successful lt blue matte glaze that
>people loved. Their most successful glazes had lots of blue and green
>although
>they kept recipes kind of a secret. Maybe it is possible to have that wide a
>range of blues and be food safe?
>
>3. Now that I have all these (in some instances, dangerous) raw
>materials, I
>am wondering how to incorporate some of these questionable test glazes into
>safer results.
>
>4. I am begging my friend not to eat off her lusterware cake plates
>that she
>got at that yard sale!
>
>This is probably a very stupid question, but if I have a dangerous glaze with
>say alot of barium, can I reglaze with a safe transparent glaze? I read
>somewhere that the safest way to get color is to use underglazes and then a
>transparent overglaze. Why wouldn't this work with regular glazes?
>
>Diane
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"
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