Craig Martell on mon 24 dec 01
Hey all you teadusters:
I was thinking about the teadust/tenmoku discussion and though I might
offer my conception of tenmokus and the difference between these glazes and
teadust.
The easiest thing to grasp is the visual difference between the two
glazes. Teadust has a tenmoku background that is littered with pyroxene
crystals. To develop these crystals, you need some MgO. Calcium doesn't
seem to go crystalline too easily without the company of a few pals like
MgO or B2O3, to name a few. There also needs to be quite a bit of calcium
in the glaze along with free silica. If conditions are right the glaze can
develop Wollastonite crystals.
To me, tenmokus are very akin to celadons but they have much more iron and
like the celadons, this iron must be dissolved and taken into solution to
achieve a dark brown to black glass. To achieve this we can use potash
feldspar with calcium as a seconday flux combined with clay and
silica. One of the important functions of calcium is dissolving the iron
and preventing it from going into a crystalline state. So, the amount of
calcium in a tenmoku has a bearing on how the glaze is going to look. If
MgO is introduced into a tenmoku your chances of ending up with a teadust
glaze will be pretty good. MgO seems to be very good at making crystals
without being the major player in the flux team. If you want to add some
MgO to a tenmoku for glaze fit, but still retain the non crystalline black,
you could try crash cooling to avoid crystal growth. That's not always an
option though. We may be quite reluctant to change our firing profiles for
one glaze or effect, but the choice is there.
regards, Craig Martell in Oregon
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