anne chambers on wed 21 aug 96
Emily,
Your post caught my attention this morning.
You mentioned green spots while talking about pop-outs. I have had this happen
occasion sometimes worse than others. Especially when using a white glaze, those
spots show up and ruin a piece. I though it was something I was doing in the st
after finally switching clay bodies the spots are gone.
What causes those green spots? They only show up at the glaze firing.
Anyone help me out?
Thanks,
Anne Chambers (Ottawa, Canada)
Emily Pearlman on thu 22 aug 96
>----------------------------Original message----------------------------
>Emily,
>
>Your post caught my attention this morning.
>You mentioned green spots while talking about pop-outs. I have had this happen
>occasion sometimes worse than others. Especially when using a white glaze,
>those
>spots show up and ruin a piece. I though it was something I was doing in
>the st
>after finally switching clay bodies the spots are gone.
>
>What causes those green spots? They only show up at the glaze firing.
>Anyone help me out?
>Thanks,
>Anne Chambers (Ottawa, Canada)
Hi Anne:
Those green spots drove me crazy for a couple 0f years, first thinking it
was me and then trying to figure out wat it was. I sopke to Julie at
Standard clay who was very helpful. I sent her several samples of both
popouts and the green spots and she said it was the grog in the clay.
Sometimes it gets contaminated in some way. She suggested I try their 205
without grog and it seem to have practically eliminated the problem, both
problems, that is.
As for it only showing up in the glaze, if you look really carefully at the
bisque pieces you can sometimes see an tiny black spot and if you can
remember where it is, nine times out of ten it will be a green or a
metallic green-black after the glaze firing if you have used a white glaze
over it.
Emily (in NYC)
Emily Pearlman-Pottery (clayfeat@echonyc.com)
http://206.4.28.2/emilypearlman
Louis Howard Katz on fri 23 aug 96
On Wed, 21 Aug 1996, anne chambers wrote:
> ----------------------------Original message----------------------------
> Emily,
>
> Your post caught my attention this morning.
> You mentioned green spots while talking about pop-outs. I have had this happe
> occasion sometimes worse than others. Especially when using a white glaze, tho
> spots show up and ruin a piece. I though it was something I was doing in the
Green spots that come through a glaze may have many sources but they boil
down to the same thing. Either iron or copper is finding it's way into
your clay or glaze.
Many (most)((all)), clays contain iron to some extent. If the pot is
fired hot enough for the iron to become liquid it can be squeezed out of
the body as the clay shrinks. Sometimes the spot of iron is on the
surface of the pot and doesn't need to get squeezed out.
Iron can also contaminate your glaze materials.
Both Iron and Copper can come from clay processing equipment. Even
Stainless Steel equipment is made of steel and bits of bearings, abraded
mill blades, bits of wire from screens, staples and many other items can
get ground and blended into your clay body or glaze materials. Copper
specks that aren't introduced in your studio come from bronze bearings
used in some large pugmills and other equipment.
In glazes often the worst of the iron will come out with fine seiving
above 80 mesh. You might be able to run your glaze over a big
electromagnet to try and collect some of the iron, but I have never tried
this.
By the way, I like green spots, so send the spots to me.
Louis
BTW Hve new computer but my network connection is flakey so I may be
offline more often than Online.
***************************************************
*Louis Katz lkatz@falcon.tamucc.edu *
*Texas A&M University Corpus Christi *
*6300 Ocean Drive, Art Department *
*Corpus Christi, Tx 78412 *
*Phone (512) 994-5987 *
**************************************************
Hendriks; Eleanor D. on sun 25 aug 96
Hello Anne,
I had terrible problems with green spots in my clear glaze until
I changed from a yellow plastic bucket to a blue one and never, never let
the stuff that dries hard on the sides of the bucket get into the glaze.
I swear there is less of that stuff in my blue bucket that there was in
my yellow bucket. Now I use the yellow bucket for my green glaze so if
there are green spots I *can't* see them!
All the best,
Eleanor Hendriks,
Elan Fine Pottery
Fergus, Ontario
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