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mason stain underglaze: need help from glaze gurus

updated sat 16 nov 02


Paulette Carr on fri 15 nov 02

Dear Ivor,

I, too, took the recipe (originally Harold Deeley's) to be a carrier
agent/fixitive for the mason stain -not oxide ... a medium for the stain
which is compatible with the firing temperature, and overglaze I plan to use.
I was hoping to use this as a typical underglaze, but at a final firing to
cone 9: I plan to paint on greenware, or bisque, whichever gives me the
visual results that I want. If I am not going to use a clear glaze on top,
then I would fire directly to cone 9. If I was planning to put a clear glaze
on top, then I would fire the underglaze decoration to cone 04 to set it,
glaze, and fire to cone 9.

David Hendley, however pointed out to me that "An "underglaze" without a
clear glaze on top of it is really no different than a "glaze".

My concerns were three-fold: If the bisqued, underglazed area is less
absorbent than the clay upon which it is painted, then glazing over this area
might produce an uneven, or unattractive glaze, as you mentioned in a
previous communication.

>> This may reduce the degree to which your bisque body adsorbs water when
glaze is
applied over your underglaze decoration. The result will be thinner
glaze, even a degree of roughness when your work is fired to maturity.>>

The second concern was that the painting medium would flux so much itself at
cone 9, that the design would run off the surface (seems as if this won't be
the case), and finally, the third concern is that this underglaze may behave
in such a way that it would cause running, and loss of design, under the
clear glaze. This concern, I will have to test with the glaze I am planning
to use. I was thinking that, if the fluxes in the underglaze were closer to
the ones that I use in my glaze (potash feldspar and wollastonite), I might
have a better chance to avoid this situation.

I hope that this answers your question, Ivor. Time for me to test the
recipe, as is. I will post my results for those who are interested.

My best,
Paulette Carr
St. Louis, MO

<* From: iandol )
* Date: Fri, 15 Nov 2002 07:09:33

Dear Ron Roy,

I'm not sure if this answer <common cone 6 glaze - it has three times the alumina and 1.7 times the
silica so - by itself it will not be overfired at cone 9. >> addresses
the question

The recipe in question is a carrier medium for the stain, to be mixed
with a stain to act as a flux which will adhere the stain to the work
when it is applied and as it is fired, which I presume is before being
fired to bisque.

I read the original post to mean the mixture was a carrier recipe, a
dilutent or a fixative. Perhaps Paulette would confirm that?

Best regards,