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washes in soda kiln

updated fri 25 feb 00


Joseph Christensen on wed 23 feb 00

I have heard about using cobalt and copper washes in
soda firing. I have never seen recipes or application
information. Does anyone have information on this they
are willing to share?
joe christensen
Minneapolis, Minnesota
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Cindy Strnad on thu 24 feb 00


I don't do salt firing, but when I apply an oxide wash, I just pour some
oxide into a cup of water and stir, then apply either by dipping or with a
brush. You have to keep stirring, because the oxides see no reason to keep
themselves conveniently suspended in such a thin medium as water. Keep in
mind the relative strengths of the oxides when deciding how much to add to
the water. Beyond that, I think it's just personal experimentation to find
out what you like. I like iron oxide for brown clay, but neither cobalt nor
copper do well there. They work okay if covered with a white
glaze--otherwise, just look black. They would likely work better on a
lighter colored clay.

Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730

Stephani Stephenson on thu 24 feb 00

----------------------------Original message----------------------------

RE: using cobalt and copper washes in soda firing.
Hi Joseph. This evening, I was perusing reading Dennis Parks' book " A
Potter's Guide to Raw Glazing and Oil Firing".. You didn't mention what
temperature you are firing to. here's a few paraphrased suggestions
from the book, which have to do with high temp firing,
Do you have a light color clay body? if so you can try applying
oxide washes straight . As a good salt body is high in silica, the
copper and cobalt washes will likely flow and bleed into the non wash
For a different effect, mix the colorants into a slip made from your
own clay body or a porcelain clay. Parks says that "German Potters have
an old rule of thumb: Add one third or more clay to an oxide" . Again,
colors will show up better on a light body or in a light color slip.
Following are a couple of slips from the book:
.Kaolin 25,
Ball Clay 25,
feldspar 25,
silica 25.
5 % copper will go red or green, sensitive to atmosphere.
1% cobalt ox. will yield bright blue.

Another Porcelain slip is
Ball Clay 10,
feldspar 50,
silica 25,
gerstley 10
talc 10
zinc 3.
The zinc enhances cobalt blues. The slip can be applied to greenware
and once fired. .Parks discusses how a desirable slip should have
enough alumina to keep the colorant and slip from running off the pot
when fumed by the salt /soda vapors. Also mentions that whiting , as a
slip ingredient, may promote blistering. And of course, much may vary
with your own claybody and firing conditions. The wonderful thing about
salt/soda is that you can be simple and loose with your formulas and
application. The stacking, the firing and the cooling will take it from

have fun
Stephani Stephenson