Vince Pitelka on mon 20 nov 06
Robert Edney wrote:
"> I've recently begun to work with terra-sig and I love it. Our main clay
> body is Laguna's Soldate 60 which I love because I tend to throw large and
> the stuff is wonderful for that. However, it does not take glaze well as
> a
> rule, which we sometimes resolve by spraying with an engobe prior to
> bisquing. In applying terra-sit (thinly with several coats) we're getting
> crackling after bisque (to 1650 F). Any ideas? We're applying the
> terra-sig at the bone dry stage and burnishing with plastic grocery bag
> material."
Robert -
When this happens, the cause is usually the application of terra sig that is
not thin enough, or simply excessive build-up of coats. Either one can
cause the terra sig to crack in the bisque fire. Terra sig should be mixed
no thicker than 1.15 specific gravity for application, and that is a very
thin liquid. Your terra sig might seem very thin in comparison to a normal
glaze mixed for dipping, but it could still be way too thick. If you do not
have a good hydrometer, get the one specified in the terra sig article at my
website at http://iweb.tntech.edu/wpitelka/professional/terra_sig.htm. It
has a range from 1.00 to 1.20, which is exactly the range needed for terra
sig, whereas most glaze hydrometers measure in a range from 1.00 to 2.00,
with far less accuracy in measurement.
Thin your terra sig to 1.15, don't apply more layers than you really need,
and don't polish until all the layers have been applied, and I think you can
eliminate the cracking.
Good luck -
- 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/
Robert Edney on mon 20 nov 06
Hi all,
I've recently begun to work with terra-sig and I love it. Our main clay
body is Laguna's Soldate 60 which I love because I tend to throw large and
the stuff is wonderful for that. However, it does not take glaze well as a
rule, which we sometimes resolve by spraying with an engobe prior to
bisquing. In applying terra-sit (thinly with several coats) we're getting
crackling after bisque (to 1650 F). Any ideas? We're applying the
terra-sig at the bone dry stage and burnishing with plastic grocery bag
material.
Thanks,
Robert
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