Alex Solla on fri 15 apr 05
Vince-
I seldom post to clayart anymore these days... seems like there are plenty of experts at the dinner table. But you just threw this dog a bone so I figure I probably should step in.
When I was at Utah State, a lot of folks were firing salt and soda with slips/engobes that were specifically designed to incorporate the sodium into them, essentially making the glaze on the fly. Wollastonite slips in particular gave specatular yellow matte surfaces. Wonderful hand. John Norris who pops up now and again on this list did some great work in this area. I dabbled a little and found some fun surfaces. For about a year I tried deconstructing my standard c10 glazes to see if I could approximate a "normal" glaze from the salt/soda firing. Found that sometimes they needed more than one firing to really soak up the necessary sodium.
In short, it is possible to make matte surfaces, with little to no crazing. Play with strontium, calcium, even lithium is worth exploring.
cheers,
Alex Solla
Cold Springs Studio
4088 Cold Springs Road
Trumansburg, NY 14886
607-387-4042 voice/fax
alexandersolla@yahoo.com
www.coldspringsstudio.com
Vince Pitelka wrote:
We have quite a few potters on this list who do some salt and soda firing,
and I'd like to hear more of a discussion on crazing in salt and soda-fired
wares. As far as I can see, it cannot be avoided, since you are inevitably
going to end up with glazed surfaces oversuplied with sodium. I know this
depends on the degree of thermochemical interaction with the claybody, but
lots of people use glazes on the outside of wares and then salt or soda-fire
lightly. In that case, crazing is common, depending on the particular
glaze. Some glazes that are matt in a reduction firing go semi-gloss in a
salt firing, with little or no crazing. Glazes that are already gloss in
reduction firing often craze badly in a salt firing. And of course, the
interior of bowls, mugs, jars, etc. must always be glazed, because the
sodium vapors do not penetrate those areas. On those vessels, the interior
glazes often craze up near the rim, where some vapors do penetrate. It just
seems to be an unavoiable problem, and I'd love to know if anyone has really
tried to tackle this problem, perhaps designing glazes undersupplied with
sodium in order to create a more balanced glaze surface in salt firing.
- 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/
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Vince Pitelka on fri 15 apr 05
We have quite a few potters on this list who do some salt and soda firing,
and I'd like to hear more of a discussion on crazing in salt and soda-fired
wares. As far as I can see, it cannot be avoided, since you are inevitably
going to end up with glazed surfaces oversuplied with sodium. I know this
depends on the degree of thermochemical interaction with the claybody, but
lots of people use glazes on the outside of wares and then salt or soda-fire
lightly. In that case, crazing is common, depending on the particular
glaze. Some glazes that are matt in a reduction firing go semi-gloss in a
salt firing, with little or no crazing. Glazes that are already gloss in
reduction firing often craze badly in a salt firing. And of course, the
interior of bowls, mugs, jars, etc. must always be glazed, because the
sodium vapors do not penetrate those areas. On those vessels, the interior
glazes often craze up near the rim, where some vapors do penetrate. It just
seems to be an unavoiable problem, and I'd love to know if anyone has really
tried to tackle this problem, perhaps designing glazes undersupplied with
sodium in order to create a more balanced glaze surface in salt firing.
- 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/
Bob Masta on sat 16 apr 05
Vince, I have never done salt/soda firing, so this
is pure speculation. But I wonder if crazing could
be reduced by adding excess boron, instead of
undersupplying the sodium. Or, what happens if
borax is tossed in along with the salt/soda?
One way to get boron to the surface of the glaze,
instead of throughout the glaze by reformulation,
might be by spray application after the main glaze
was applied, using thin, fast-drying coats. I
imagine it would be easy enough to just feather a
little onto the inside of the rims, as needed.
Another way instead of spraying would be to
mix up the borate (borax or whatever) in a
non-aqueous base such as salad oil, and dip or
brush it on over the normal glaze coat. I haven't
actually done that (over a regular glaze), but I have
applied oil-base glazes over bone-dry greenware.
(This was to avoid cracking, since the oil doesn't
rehydrate the clay and cause it to expand like water
based glazes do.) Anyway, the oil soaked into
the piece and left its glaze load on the surface in a
very powdery layer... like butterfly wing scales.
The oil of course burns out in firing, and the glazes
in my case turned out just fine, apart from a few
unavoidable handling marks. (Adds a personal touch!)
I'm thinking that athin coat of borax over the surface
of the glaze coat would balance the sodium from the
salt/soda vapor. But it might also change the whole
character of the effect. For good or bad? If anyone
ever tries this, please share the results here!
Best regards.
Bob Masta
potsATdaqartaDOTcom
John Britt on sat 16 apr 05
I think it is impossible to create a craze-free surface in soda and salt,
because of the unpredictable amount of salt and soda that is put in the
kiln, volatilized, or taken up by the pieces in the kiln. Also, every time
you fire you are adding more salt or soda and the kilns get =91juicier=94 an=
d
so you never know how much you are getting on your ware.
If someone can figure out how to do this regularly it would be amazing,
Just my opinion,
John Britt
www.johnbrittpottery.com
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