Nancy Sowder on sun 6 nov 05
I have a base glaze to which I add mason stains, tin oxide and rutile to
get variegated colors. The tin oxide, or the combination of tin and
rutile is sometimes turning the colors a harsh yellow with a sort of
pearly sheen. The turquoise may fire completely yellow or chartreuse.
The problem may be limited to clay bodies with a little iron, as it is
worse on buff stoneware than on porcelain or white stonewares. It is more
pronounced the more thoroughly the tin is mixed into the glaze.
The glaze is cone 6, oxidation
ferro frit 3292 (54%),
and small amounts of talc, strontium, and silica,
3% tin oxide, 4% rutile and 7% mason various mason stains.
If anyone can help me, I would like to know why it sometimes turns yellow
and if there is any way to stop it from happening.
Richard Aerni on sun 6 nov 05
On Sun, 6 Nov 2005 13:18:32 -0500, Nancy Sowder wrote:
>The glaze is cone 6, oxidation
>ferro frit 3292 (54%),
>and small amounts of talc, strontium, and silica,
>3% tin oxide, 4% rutile and 7% mason various mason stains.
>If anyone can help me, I would like to know why it sometimes turns yellow
>and if there is any way to stop it from happening.
I'm afraid I won't be terribly much of a help here, as I don't fire in
oxidation or at cone 6, but I do have a glaze that I fire in a gas kiln to
cone 10 that has a healthy dose of tin and rutile in it. I can't remember
the exact proportions, as my computer is not at the studio but at home, so
the recipe isn't handy.
Anyway, that glaze goes a lemony yellow in the parts of the kiln that tend
to fire in a neutral atmosphere. In the reducing part of the kiln, it is a
pearly bluish white. So, tin and rutile together can make yellow.
If you are looking for a variegated result, maybe you should drop the tin
and stick with the rutile alone, or else do a line blend of the two
ingredients to see how the glaze behaves with different proportions of them.
As for the Mason stains, I can't say what's going on, since you say you use
various Mason stains. It would baffle me to put in a blue or red stain,
say, and end up with a yellow glaze, however.
Hope this helps, at least a little bit. I'm not a theoretical glaze guy.
If I have ideas on how to change things, I tend to test them in an organized