Vince Pitelka on sat 11 jan 97
The thread which began with the bee-weed suryp has been fascinating, and I
especially appreciate John Guerin's posts. John explains that the Pueblo
potters doing blackware use a red slip in order to get a darker black. I
have seen this in the various books on the work of Maria, Margaret Tafoya,
etc. But we have had an interesting experience using terra sigillatas. I
have taken to using terra sigs as burnishing slips, as they work better than
any other burnishing slip I have ever used. But in the starved-reduction
blackware firing we get a much darker, denser black with a ball-clay terra
sig than with a redart terra-sig. This is with terra sigs prepared as I
have described previously, to give ultra-fine particle size. Both sigs
burnish and polish very well. The redart terra sig, whether burnished or
polished, usually gives varying shades of smoky red/black, which is very
beautiful. But in the same firing, the ball clay terra sig will give a
wonderful dense jet-black. What's going on here? Any ideas?
- Vince
Vince Pitelka - vpitelka@Dekalb.Net
Phone - home 615/597-5376, work 615/597-6801
Appalachian Center for Crafts, Smithville TN 37166
Darrol F. Shillingburg on wed 15 jan 97
Hi Vince,
I think the color difference is caused by the iron content of the tera
sigillata. I have been saggar smoking white stoneware clays 'glazed' with
mixtures of sigillata made from Laguna's SBRed clay diluted with sigillatas made
from OM4 and from Kaolin. (SBRed is a midrange high iron clay body)
The firing process is very simular to that used in your Ancient Clay workshops,
but uses covered metal sagger buckets in my kiln with a burner under them until
they are 'smoke'n'. Nevertheless, they are 'oxygen starved' carbon firings. When
mixed with OM4 sigillata the SBRed sigillata yields a beautiful range of 'red
browns' in the carbon firing process. It look simular to what I remember comming
from your 'smotherd bonfiring' of redart sig pots. I have not tried the mixture
beyond 'half and half', but it might prove interesting to do so.
All vessels are bisque to cone 012 before carbon firing.
The reactions of high iron content sigillatas to higher temperatures (cone 5)
and to 'reduction cooling' atmospheres seems to me a different discussion. I
have done just enough experimenting to know that the clay body and the sigillata
react differently to 'reduction cooling' atmospheres, but not enough to
articulate the reasons. ( I suspect density)
Darrol in snowy Elephant Butte NM
On January 11,1997 Vince Pitelka wrote:
>The redart terra sig, whether burnished or
>polished, usually gives varying shades of smoky red/black, which is very
>beautiful. But in the same firing, the ball clay terra sig will give a
>wonderful dense jet-black.
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