Snail Scott on thu 24 may 01
At 12:39 PM 5/24/01 -0600, you wrote:
cups (unomi) made out of a new
>(to me) native white clay that I had slipped with different native white
>slip, bisqued and then glazed with a carbon trap glaze of my own
>formulation... I was quite surprised when I
>opened the kiln to find a very different glaze, albeit roughly the same
>color...
>William A. Lucius
>President and Executive Director
Seems to be that carbon-trap is all about outgassing.
That underlying clay has lotsa stuff in it that's
gotta get out somehow, and a carbon-trap glaze is
pretty much designed to catch at least some of it.
I woulld think that clay-glaze surface interactions
are a minor component of the final outcome.
-Snail
William Lucius on thu 24 may 01
I just unloaded my cone 6 to cone 7 moderate reduction firing from my
natural gas, stacked ring, soft firebrick kiln (a candidate for the dump).
It was my first firing this year, because our grandson's kindergarten class
tiles had to be fired before the end of the school year. In order to fill
out the kiln I added a series of teapots and cups (unomi) made out of a new
(to me) native white clay that I had slipped with different native white
slip, bisqued and then glazed with a carbon trap glaze of my own
formulation. Since I have been using this glaze for several years I know
its range of variation on this particular slip. I was quite surprised when I
opened the kiln to find a very different glaze, albeit roughly the same
color. I had noticed this change in a previous test firing, but since I
graph every firing to create a time/temperature curve and this one was not
significantly different, I would guess that what I am observing is a
glaze/body clay interaction through the relatively heavy slip. I have read
that the glaze only interacts with the topmost layer of body clay (i.e, the
slip in this case). But I wonder if the actual case might be much more
complex. And if clay bodies and glazes do interact through a slip, it might
explain some of the glaze variations that I have noted with other native
clay combinations that I have worked with. Has this issue been discussed
previously? Do any of the technical wizards have any opinions?
I will only be here for a few more days to check on responses. Then we (my
wife and I and 16 Forest Service Partners in Time volunteers) are due to
visit with the Ancestral Pueblo (Anasazi to the politically incorrect)
potters who made redware pottery in Southeastern Utah. No matter that they
have been dead for over a millennium - their clay mines and kilns are what
we are looking for. We will have not access to e-mail, so I will have to go
off the list for the month of June.
William A. Lucius
President and Executive Director
Institute for Archaeological Ceramic Research
845 Hartford Drive
ilwwal@hotmail.com
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