JUDY THOMPSON on thu 10 oct 96
Here is a question whose answer I hope will solve a problem we are
having in our teaching studio.
When students use cobalt carbonate, cobalt oxide, or a cobalt based
Mason Stain for onglaze decoration, the cobalt seems to spatter
downward while firing in the electric kiln to Cone 5-6. Almost
every time cobalt is used to decorate over glaze, the pieces come
out of the kiln with speckles of blue misted over the area directly
around, or under, where the decoration was applied. Is this
getting spattered when it is applied (it doesn't show up when raw);
or is the cobalt volatizing in the firing and spattering then?
Whatever the cause, we need a solution to this problem. Can anyone
shed a little light?
Lisa on thu 10 oct 96
JUDY THOMPSON wrote:
>
> ----------------------------Original message----------------------------
> Here is a question whose answer I hope will solve a problem we are
> having in our teaching studio.
>
> When students use cobalt carbonate, cobalt oxide, or a cobalt based
> Mason Stain for onglaze decoration, the cobalt seems to spatter
> downward while firing in the electric kiln to Cone 5-6. Almost
> every time cobalt is used to decorate over glaze, the pieces come
> out of the kiln with speckles of blue misted over the area directly
> around, or under, where the decoration was applied. Is this
> getting spattered when it is applied (it doesn't show up when raw);
> or is the cobalt volatizing in the firing and spattering then?
>
> Whatever the cause, we need a solution to this problem. Can anyone
> shed a little light?
I have had this same problem many times, but have not found an answer.
One also has to be careful not to get even the HINT of cobalt on the
fingers, or one gets fingerprints and cobalt smudges where they're not
wanted.
Cobalt1994@aol.com on thu 10 oct 96
Hi Judy,
I Use cobalt wash on top of my glaze all the time and never get splattering.
I wonder if it's your particular glaze bubbling alot as it melts in the
firing and causing the splattering.....try a different glaze.
Jennifer in Vermont
*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*
email: Cobalt1994@aol.com
Jennifer Boyer
Thistle Hill Pottery
Montpelier, Vt.
~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~
Bonnema on fri 11 oct 96
We were having the same cobalt splattering problem at cone 9 reduction over
one particular glaze. I asked Pete Pinnell about it at a workshop last fall
and after looking at the glaze formula he thought that it was the boron in
the glaze that caused a lot of boiling during the melt. (At least that is
how I remember his answer). Do you have gerstley borate in the glazes?
Garret Bonnema
--
Garret Bonnema
bonnema@bdc.bethel.me.us
Suzanne Storer on fri 11 oct 96
Cobalt is a renegade in the kiln. In the firing it spatters about. I make
sure the pieces with cobalt on them are fired near others that won't mind
some spots on them. I've also found that glaze that collects into little
spots when applied over wax on convex surfaces (rims are an extreme example)
shoots off the surface in the fire and lands on the ware around it just like
cobalt.
Hello again after a years leave. I'm still getting garden tomatoes here in
mountain Utah. No hard freeze by now is amazing.
>----------------------------Original message----------------------------
>Here is a question whose answer I hope will solve a problem we are
>having in our teaching studio.
>
>When students use cobalt carbonate, cobalt oxide, or a cobalt based
>Mason Stain for onglaze decoration, the cobalt seems to spatter
>downward while firing in the electric kiln to Cone 5-6. Almost
>every time cobalt is used to decorate over glaze, the pieces come
>out of the kiln with speckles of blue misted over the area directly
>around, or under, where the decoration was applied. Is this
>getting spattered when it is applied (it doesn't show up when raw);
>or is the cobalt volatizing in the firing and spattering then?
>
>Whatever the cause, we need a solution to this problem. Can anyone
>shed a little light?
>
Gerry Barbe on sat 12 oct 96
Hi,
I've had the same problem with cobalt, so has our Guild. Always
wondered what the problem was and am glad to find out!!! One more
observation though: the cobalt which spattered on the kiln shelf will
return to haunt you during the next glaze fire. That's right, it will
spatter off the shelf and onto pots that don't have even a hint of blue on
them. What I do is put kiln wash over the spatters on the shelf to make
them stay put.
Great, informative discussion....
Yours, Marilyn getting ready for Thanksgiving in Ailsa Craig, ON
Canada
______________________________________________________________________________
| |
|
