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salt questions

updated sun 2 mar 08


John Boyd on sat 1 mar 08

Teri and interested parties,
It is possible to single fire
anything, provided you take the time and necessary steps to avoid errors.
Firing in a soda kiln was my senior thesis in college; I single fired many
works to monopolize on the usage of the kiln. Double the time between
turning up the gas until you clear bisque temperatures. Bisquing saves time
and allows you to tumble stack with less shrinkage. I recommend tumble
stacking to variate your fired results.
Flashing slips and firing pots in fluxed and variable atmospheres seem
to go hand in hand. There are too many recipes to list, but in my first
year of ceramics I went to and searched the Clayart archives
for recipes. Almost any Ceramics Monthly article on sodawerk will have
something interesting to try. A potter in Seagrove once told our visiting
class, "Every time you fire the kiln you should be putting in test tiles."
I think I tend to agree.
For a quick start, look up Bauer's Orange Slip. I used this at the
thickness of milk on Hestia clay by Highwater, with Gail Nichol's soda mix
on wood slats @ cone 9 flat to cone 10 tipping with a crash cool when 10 is
flat. That should give you the initial citrus soda rush, with some
unexpected colors coming from stacking and location.
Any Glaze can be exciting in the soda kiln, here's a list of what we
used at Guilford: Tomato Red, Willie Helix, Tenmoku with a little wood ash
sprinkled here and there, A stiff white Shino that picked up copper flashes
when next to Helix glazed pots, Bauer's Orange slip, White Crackle slip,
Saint John's Black, Shino type glazes for liners, Reeve's Green for
decorating, and colored slips.
Salt reacts with oxide stains, but it depends on what you mean by
"well." If the oxide is a mat of color, then you will probably love the
side facing the soda, and shrug at the static side. If you have painted
imagery, the side away from the salt will probably make you smile, the side
facing the salt will probably beak and run.
Any of the salt introduction procedures you list will work; it depends
on the aesthetic result you want. A quick, generalized thinking strategy
for this is:
Less sodium= drier surfaces, more available color range
More sodium= wetter surfaces, narrower available color range
Dry (non hydrated) salt= slow dispersion, localized vapors, some steam
Wet (hydrated) salt= rapid, gaseous dispersion with heavy vapor traveling
through steam
Wood= adds vapors and fluxes of its own, flames waft around kiln
Sodium carbonate compounds= softer surfaces, more available color range
Table salt and non carbonated compounds= wetter surfaces edging towards
glassy, narrower available color range
As with any ceramic process you select variables and manipulate them
towards an aesthetic goal, everything is a test. Calcium in the form of
whiting, will add fluxes to the sodium, affecting colors and surfaces.
Iodized salt is usually in the form of potassium iodide; potassium being a
flux and present in many shino type glazes, you can already guess at the
color range it can provide.
If you use flashing slips over everything at milk like consistency or
thicker, it will matter little what type of clay body you use. If you are
using thin washes of slip, or you aim for purity of glaze color, a
porcelain, or white stoneware should be your starting point. If your slip
is low iron, or you use a lot of shino type glazes, you may want to move to
a grey stoneware. Most of the orangey-brown bodies in gas will come out
heavy purple/red brown, like a lacquered chocolate bar, unless you are set
up to reduction cool the kiln.
The toxicity of salt vs soda, along with many of your questions, is
explored in Phil Rodgers excellent book on salt firing. For you, at this
point, I would highly recommend this book as your starting point.
The advice I would give to someone exploring a new field: Heavily
cultivate your curiosity, your ability to take notes, and an inexhaustible
Best of luck,