Stephani Stephenson on sun 14 dec 03
Theresa wrote: "The colors also seem to wash out of the single fire
glazes. They are not consistent when I try to reproduce them.
Hi Theresa
It sounds like the glaze is fluxing and sealing the clay surface before
all organic compounds are properly combusted. Not allowing gases out or
oxygen in.
Aside from the question of bloating and pinholing, oftentimes the same
glaze does not look the same when applied and fired on greenware v.
bisqueware.
One difference is that Greenware is not as porous as bisqueware, so
water is not absorbed into the clay in the same way, at the same rate,
or to the same depth .
This affects the way soluble materials are absorbed into the clay.
Let's say it also affects the way the applied glaze 'rides ' on the
clay, for lack of a more technical term.
Freshly applied glaze will tend to remain in liquid state a bit longer
on greenware, the water remains in suspension on the surface a bit
longer and evaporates into the air rather than being absorbed through
the clay readily, as with bisque. I think, in certain glazes, this
affects the way particles in suspension settle and move about in the
glaze before they are 'frozen' in action by the drying of the glaze
coat.
I have tested many glazes side by side on bisque and greenware: same
glaze, same clay. With some glazes there is little difference, with
others there is marked difference. Sometimes one will look thinner and
'washed out after firing; or one will look more fused to the clay body
than the other,etc. I have also tried some commercial glazes which
crawl on greenware surfaces.
I have one glaze which pinholes easily.. these pinhole bubbles form
during application, rather than firing, and are difficult to smooth
over with finger.They tend to remain through the firing , as this is
not a very fluid glaze.When applying this glaze to bisque, I wet the
clay, wait till water vanishes, then glaze... a typical technique.
When I tried applying this glaze to greenware thousands of bubbles
would appear on the surface upon application. So, I started wetting
the greenware slightly before applying glaze and found that it solved
the problem..
You do have to be very careful not to add TOO much water.I very very
lightly dunk just the surface, or spray it with water, very lightly,
then apply glaze.This is a very particular glaze. I find glazes to
have very distinct 'personalities' , in this regard.
Anyway, it seems to me that the physical interaction of clay and glaze
during application , as well as interactions during firing, cause
differences in fired appearance.
sincerely
Stephani Stephenson
steph@alchemiestudio.com
Teresa Testa on sun 14 dec 03
Thanks for all your suggestions. I will modify my firing schedule and let you
all know how it works. I also like the suggestion of lightly spraying the
greenware with water before the glaze application.
Teresa,
Windancer Studio, Las Vegas NV
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