Kayo Parsons-Korn on fri 13 nov 98
I read Don Goodrich's comments on this and went to the website he
suggested, http://members.aol.com/goodrichdn/acfc1.htm. When I took
Vince's class we applied terra sig over the clay body and I suspect the
pieces Don's group made did so as well. So really what you are looking
at is not the clay body itself, but the terra sig. (Just a
clarification.)
We made the sig out of redart and goldart clay and I know Vince has
posted the method of making the terra sig before. I believe Vince
mentioned, and I believe it is true, the goldart was more likely to go
absolutely black in the firing than the redart. As you can see in Don's
photos, many of the pots are not absolutely black.
If you have ever seen color pictures of Maria Martinez making pots,
you'll notice her clay is a very red clay. But I have made pots out of
clay mined near Showlow, AZ where the clay is very yellow and fires out
red in oxidation and black when reduced.
So here's question to the clay gurus like Ron Roy and Vince. Does the
iron content of the clay have anything to do with how black a pot will
reduce? Or is it more likely the firing method which determines whether
a pot will go totally black. I've started to reduce the amount of
sawdust in the reduction materials and increase the manure. Recently I
read where Maria Martinez just used manure and the ashes from previous
fires for her reducing medium.
--
Kayo Parsons-Korn
Kayo Parsons-Korn Design
kayo@kayodesign.com
http://www.kayodesign.com
(503) 647-5464
P.O. Box 436
North Plains, OR 97133
Vince Pitelka on sat 14 nov 98
Thanks Kayo for clarifying several things.
>I read Don Goodrich's comments on this and went to the website he
>suggested, http://members.aol.com/goodrichdn/acfc1.htm. When I took
>Vince's class we applied terra sig over the clay body and I suspect the
>pieces Don's group made did so as well. So really what you are looking
>at is not the clay body itself, but the terra sig. (Just a
>clarification.)
That is correct. That claybody (equal parts goldart, ball clay, fire clay,
and extra-fine grog) does not burnish especially well by itself, because it
is so gritty. Anyone wanting info on my terra sig process can find it at
Tony Hansen's IMC webpage at http://digitalfire.com/education/glaze/terasig.htm
>We made the sig out of redart and goldart clay and I know Vince has
>posted the method of making the terra sig before. I believe Vince
>mentioned, and I believe it is true, the goldart was more likely to go
>absolutely black in the firing than the redart. As you can see in Don's
>photos, many of the pots are not absolutely black.
Actually, the most intense black is achieved with the ball clay terra sig,
but if there are any areas which do not go black, they will be white or
gray. So it really depends on what combination of colors you want on the
surface, just in case the pot does not go completely black. I prefer the
range of red-browns which the redart sig gives when it does not go pure black.
>If you have ever seen color pictures of Maria Martinez making pots,
>you'll notice her clay is a very red clay.
I am not sure about this. All the images I have seen show Maria using a
buff body, which is pretty standard among Pueblo potters. The slip she
applied for her black-on-black pots was very red.
>So here's question to the clay gurus like Ron Roy and Vince. Does the
>iron content of the clay have anything to do with how black a pot will
>reduce? Or is it more likely the firing method which determines whether
>a pot will go totally black. I've started to reduce the amount of
>sawdust in the reduction materials and increase the manure. Recently I
>read where Maria Martinez just used manure and the ashes from previous
>fires for her reducing medium.
As far as I know, it is particle size rather than iron content which
determines the amount of carbon admitted into the clay surface. As I see
it, the redart terra sig, prepared properly, is composed of the very finest
fraction of particles, and it makes a VERY dense surface, especially when
burnished. The ball clay has a much finer average particle distribution
before making terra sig, and therefore it is harder to separate out the
finest particles. Ball clay gives a very high yield of sig, but the average
particle size is considerable coarser than with the redart sig, where the
coarse particles settle out easily during the preparation process.
Maria uses pure crushed manure dumped on the firing to make the necessary
smoke, and then the whole pile is smothered with ashes accumulated from
previous firings. In my experience it does not make any difference whether
you use all manure, or half manure and half sawdust. It is important that
it be bone dry, and that it be finely pulverized.
Good luck -
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Don Goodrich on sat 14 nov 98
Kayo,
You make a good point abou the terra sigillata used in Vince's Ancient Clay
class. We used two sigs, made from redart or from ball clay. However, some of
the pots our group made were burnished without it, so we could compare. It
turned out that burnished pots without terra sig developed a similar smooth,
shiny surface. The sig just required a lot less work, since polishing with a
rag was sufficient.
It appears that the goldart body without a redart coating does produce a
deeper black. I visited Lisa Skeen's place a couple of weekends ago, where we
pitfired and manure-smothered several pots made of Vince's clay, with no terra
sig. The well-smoked areas of these pots, whether burnished or not, are truly
black, without the red tint that appears in those having the redart sig one
can see in the website photos.
I've fired clay from the Acoma Pueblo in an open, loosely stacked fire of
cow pies and had it turn out white. The same clay turns out black if the fire
is smothered in horse manure.
The best-blackened work I've fired was a batch of small medallions made of
dark red clay from central Wisconsin, fired in tightly-stacked newspapers
under a bonfire for several hours. All this leads me to conclude that firing,
or rather the smoking method, contributes most to blackening.
Hoping to see some guru responses,
Don Goodrich
goodrichdn@aol.com
http://members.aol.com/goodrichdn/
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