Susan Hearn on fri 9 feb 07
Does anyone have a white terra sig that goes up to cone 5? Thanks.
Susan Hearn
Vince Pitelka on fri 9 feb 07
Susan Hearn wrote:
"Does anyone have a white terra sig that goes up to cone 5? Thanks."
Susan -
The answer depends on what you want from a terra sig. If you want the kind
of shine available at lower temperatures, then it's an impossibility - there
is no such thing as a terra sig that will maintain a high shine to cone 5.
The shine on terra sig depends on a compact layer of very fine particles,
and if the substrate claybody shrinks to any appreciable degree, the shine
is lost. The best terra sig shine will not survive above about cone 08.
However, if you just want the silky finish of a terra sig, without the
shine, then any kaolin terra sig will serve well at cone 5. Read my article
at http://iweb.tntech.edu/wpitelka/professional/terra_sig.htm for guidelines
of how to make a superior terra sig. Keep in mind that kaolins give
relatively low yield, because of the coarseness of particle size, and you
can drastically increase the yield with a ball mill.
You can also get a very high yield of terra sig from Tennessee ball clay,
with only slight discoloration at cone 5. For the whitest, white, use a
kaolin like Grolleg, EPK or Tile 6. If that's not such an issue, use
Tennessee ball clay.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Snail Scott on fri 9 feb 07
At 09:57 AM 2/9/2007 -0800, you wrote:
>Does anyone have a white terra sig that goes up to cone 5?
The propery of terra sigillata that most
people value it for - the high shine -
will be compromised at ^5. Any but the
slightest sintering or melt of the clay
it's made of will diminish the shine,
as the particles start to fuse and shift
against each other. This process begins
around ^012 or so, and every incremental
increase in temperature will reduce the
shine a little bit. Even when made of a
high-temperature clay like a kaolin, this
will be the case. The terra sig will
retain some effect, and look smoother
and different from a regular clay
surface, but it won't look like a
terra sigillata would at its usual
temperature.
-Snail
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