[Clayart] Pinhole problems with Temmoku Gold ^6

[Robert L. Johnson via Clayart]

I'm having occasional trouble with the cone 6 Temmoku Gold glaze, based on
the following recipe:

*TEMMOKU GOLD* Cone 6 reduction

67.41 Cornwall Stone

8.98 Whiting

3.37 Gerstley Borate (I substitute Frit 3134)

6.17 Lithium Carbonate

7.86 Dolomite

6.17 Silica

Add: 11.24 Red Iron Oxide

Most of the time I get good results with it, but I do lose pots to
pinholes. So. I'm looking for suggestions. Here are some things I've
considered:

- I like to use it in oxidation (often with Ron Roy's Sky Blue) because
I like just a sprinkling of iron crystals.
- It seems like the pinholes occur in pots higher up in the kiln and on
the right side. I have an 18 cu ft, two burner downdraft kiln, so maybe the
flame from the burner on that side could be the culprit?
- I occasionally have a pinhole problem with a teadust glaze, too--so
perhaps these tenmokus are temperamental.
- I have tried reglazing and refiring, but that seems to create even
more pinholes. This suggests that glaze thickness could be the problem.
- I use B-mix, so perhaps there is some interaction with the clay.
- Also, I hear that porcelain could cause some spalling in an aluminum
pugmill, and B-mix is a cousin to porcelain, so could my old PeterPugger be
the problem? (I do occasionally see little hard black things in my clay.)

So where--if anywhere--to start?
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[ronroy--- via Clayart]

Hi Robert,

Put some cones around in your kiln to see what is happening in that corner.

Pin holes are blisters from escaping gases - if the glaze freezes
before the craters heal over you get pinholes. Keep the glaze fluid a
little longer to let those holes heal over. Firing down for 30 minutes
may do the trick.

RR

Ron Roy
ron...@ca.inter.net
Web page ronroy.net

[David Finkelnburg via Clayart]

Robert,
Ron Roy is pointing you in a good direction. To add to what he wrote, you
are using two potentially problematic ingredients: the frit and lithium
carbonate. The first has already been molten once so it melts easily the
second time around. The second has a lower melting point than any other
ingredients in your glaze recipe. The combination gives you a glaze that
melts, at least partly, early in the firing, Ron's suggestion, to keep it
molten longer, would be good to test before trying the other things on your
list. Good firing!
Dave Finkelnburg

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