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cone 6 vs. cone 9 ox - #2

updated sun 16 apr 00


Bob Hamm on sat 15 apr 00

Hi Linda

I am sorry for the delay, but I was handcuffed by a modem problem.

I am not sure what kind of texture you want to enhance, so I will just let
my mind ramble and write out some ideas. I hope some will be new to you and
will generate more ideas of your own.

Just a couple of comments about texture.

Think about mountains and reefs in the ocean. If they are high enough, not
even the muddiest water can hide them. If they are under the surface, the
water would have to be fairly clear to see them. And if they are under the
water, they would be easier to see if they were bold and crisp. A muddy
sandbar is less interesting then sharp rocks and coral. So make the texture
bolder if your glaze is matte, or choose clear or translucent glazes for
delicate texture. If your texture is applied, maybe coloured clay could
help define the texture from background. Think of all that colourful coral.

Once you have your texture, try staining it with oxides or glazes, then
apply an over-glaze. There are two approaches to staining - staining the
valleys or the top of the hills.

The valleys: If your clay body is light, choose darker stains and a glaze
that is darker then the body. Try the opposite for darker bodies, with a
light engobe in place of the stain. A glaze that is even a bit fluid can
run off the high points, so the clay would show through the glaze. Try a
clear or translucent glaze over delicate texturing. A matte may work over
bolder texture. This is the way a Celadon defines texture - dark valleys,
bright hilltops.

The hilltops: Airbrush or mist the pot with a contrasting stain. If you
just let the mist drift down over the pot it will collect on the high
points. This is the opposite effect of staining the hollows. If your glaze
is applied thinner on the high points ( I will say more about this later)
the stain will easily penetrate the thin areas, and will be absent or buried
where thick. I have done this with a fairly opaque off-white matte over
iron, and was rewarded with clear definition of the fine lines a sponge
leaves when wiping excess slip off the side of a pot. A fine mist and care
is required.

You could try the celadon approach. Choose a clear glaze that is somewhat
fluid, but controllable, and let the glaze run off the hilltops and into the

You can also enhance texture by using the glaze's tendency of breaking over
edges. Some glazes are different when thin, like a Tenmoku. In oxidation
we can use these effects as well. Thin glazes seem to resist crystal
development. It is not too difficult to create glazes that will develop
crystals where thick, creating a matte surface, but remaining gloss where
thin. This is most easily done by controlling the firing cycle. Firing up
slowly and slowed cooling will ensure a good melt, and allow time for
crystallization on the way down. You will need to experiment to find out
the cooling cycle for a particular glaze. Try starting with a slow cooling
from about 1050'C to 950"C, staying in this range for 4 to 6 hours. Some
gloss glazes will completely matte out with this treatment. The nice thing
about this type of glaze is you get contrasts. Gloss and matte and the
different tactile feel of each. In a coloured glaze the crystals are almost
always a different colour than the background glaze, so you also have
contrasting colours.

If you are applying the glaze by dipping, you can sometimes thin glaze on
edges during application by swirling the pot in the glaze bucket, just
before you take it out. This can wash some of the glaze off the high edges.
A longer count during dipping may help, as this will allow the edges of the
clay body to become wetter, making it harder for the edges to hold the
glaze. This works better on fine clays, because you do not have to worry as
much about rough edges. You could also try lightly buffing the pot with a
rag, to thin the glaze on the edges.
These last ideas would work best on bold textures.

Regarding the floating blue - I have not tried this glaze, so I do not know
what it looks like; but from your description it is the kind of glaze I
would want. My choice of a base glaze would be a clear gloss glaze I could
matte in the kiln. It could be coloured and fired gloss like a celedon.
Opacifiers could be added to control opacity and create different surface
qualities and different reactions to the same colorants. You can create a
book of glazes from one good base. My suggestion would be to pick two or
three, with different primary fluxes and experiment. By working with this
limited sample, you will be surprised at how fast you can learn, and the
number of quality glazes you end up with. A small test kiln and glaze
calculation software, makes this a lot easier. I will be posting a pair of
glazes soon.

Time to stop, my mind is going mushy.

Good luck

Bob Hamm
Super Mud Works
Kelowna BC Canada
Ph 250 765-8876