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underglaze vehicles

updated mon 18 nov 02


iandol on sat 16 nov 02

Dear Palette,
I go along with your ideas fully and can see no technical objection to =
I would disagree with David Hendley. I think that an underglaze carrier =
should be as close a match in composition to the underlaying body as =
possible and it should have almost the same degree of vitrification, =
when fired to maturity, as the clay on which it sits. This works well if =
you are using a white or porcelain body.
As I recall, the recipe you posted would need to be pushed high to =
become anything like a glaze. It might approach being a vitreous engobe =
if used on bisque ware but I could not imagine it becoming transparent.
My own measurements are a bit rough and ready, sort of spoonful style, =
when making coloured slips with Stains. I include a good proportion of =
my white clay, say four fifths and one fifth soda-felspar. This goes =
with the stain on a one to one basis for a full strong effect, or it is =
diluted more for pastel tones. If I overfire the bisque, say going to =
cone 06 instead of 08 then I get the resist effect you speak of, which =
gives a thin patch on the glaze. I could allow for this by decreasing =
the Felspar. I would never add a boron based frit as a flux into a =
carrier used on stoneware or porcelain. My fluid vehicle of preference =
is Water with 20% Pure Glycerine and about 10% strong liquid Gum Arabic, =
Acacia or Trag. Flows well from the brush and adheres without powdering.
Carriers with the minimum of flux should not flow at maturity. If it is =
going to do this it will do it whether or not there is glaze over the =
Look forward to learning about your results.
Best regards,