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soda problem

updated fri 9 feb 01


Joseph Michael Christensen on thu 8 feb 01

I have been working with soda glazing for about a 15 months now
and have run into a problem that no one I know can answer. I have been
firing in about thirty cu. 30 kiln that is fueled with natural gas. I
spray in about 5 pounds of
baking soda. I use a clay body that is a mixture of a pre-mixed grolleg
porcelain body and a buff stoneware body that has a little iron.
The mix is about 50/50. The body, in combination with a simple shino
like slip usually gives me some very nice results. I start
reduction at 010 and reduce all to about cone 9 and let the kiln finish
off in oxidation at cone 10. I have been getting some nice
carbon trapping and some very nice soda build up .
The problem that has happened in the three of my last 4 firings is
that a rough surface has built up on the areas where the soda
has gotten concentrated. I have always gotten smooth surfaces until now,

despite the amount of soda build up. I am of the aesthetic
that the more soda the better on my pots. The rough surface looks like
little black spots that feel like sandpaper. The difference in
the three bad firings is that I put in three small cups of copper
carbonate (about 20 grams )in the kiln before I fired looking for some
copper flashing. Can the copper, in combination with the spraying of the

soda cause this? I am completely in
love with soda glazing.
Thank you -Joe Christensen