vince pitelka on sun 22 apr 01
Elca -
Attic red-black wares were fired in domed updraft kilns. The decoration was
done in a thin terra sigillata. The following is my favorite theory,
although I am not sure anyone knows for sure. The red coloring came from
the terra sig by itself. The black coloring was from the same terra sig,
but mixed with an alkaline solution obtained from soaking wood ashes, which
would introduce soda and potash. As the firing approached maturity the
potter reduced the kiln, which turned all the red ferric iron in the clay
and terra sigs to black ferrous iron. At the top of the kiln, just inside
the exhaust flue, the potter placed a series of draw trials, which were
removed one at a time as the kiln reached temperature. As soon as the
fluxed black terra sig showed signs of vitrification, the potter ended the
firing. As the kiln cooled, the unfluxed, unvitrified red slip reoxidized
back to red ferric iron, while the fluxed vitrified black slip retained the
black ferrous iron color. There are plenty of examples of Greek pots that
were overfired, where all of the terra sig vitrified and remained black, and
other examples which did not quite reach temperature, where areas of the
black sig reoxidized to red.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
| |
|
