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salt glaze

updated sat 10 mar 01


craig schuster on sun 2 may 99

HI everyone. I have been reading and enjoying the discussion group for a =
while now.

What I am currently looking for is a nice medium blue salt glaze (not =
or dark blue). If you have seen Jane Hamlyn's beautiful work, well that is =
blue I'm after.

I would call myself relatively inexperienced salt firer (we fire in a =
kiln), so would appreciate any hints on glaze,slips, firing etc.

Hoping you can help and thanking you all in advance.

Carole Steele on mon 3 may 99

Craig=3B I use a commonly known glaze called
=22Gilbert's Blue=22 which is a wonderful dark blue
in cone 10 reduction firing and soda firing. I
achieve similiar results in both. It should work
in salt firing as well. Post me offline if you want
a 300 gm. test recipe.

Carole in Louisiana
Graduating from college (again) and going on for
my MFA, then retiring in the mountains of ????
to make pottery and enjoy the views=21

philrogers on fri 21 jul 00

I have been experiencing a recurrent problem in my salt kiln and
wondered if anyone might have had a similar problem.

Pots are coming out with dark, often matte or rough patches on the side
of the pot that faces the fireboxes. The slips most affected are those
higher in alumina ( high silica slips are unaffected ).I fire with 28
sec domestic heating oil. Reduction commences at Cone 06 and salting at
Cone 8. I keep the kiln as clean as possible upto Cone 06 and trials
drawn at that point show no sign of carbon deposit.

The first four firings in this kiln were perfect, barely a second in
sight. I have therefore come to the conclusion that the problem is in
some way connected to the rise of residual salt as this would not have
been present in the early firings. Is this a problem associated with
carbon or could it be sulphur related. The area of the pots affected
look as if the slip surface has been unaffected by the fluxing action of
the sodium yet it is always the side of the pot that faces the main
draft of the salt that this happens to.

The high alumina slips ie. 1/3 China Clay, 1/3 Ball Clay, 1/3 Nephaline
are meant not to be shiny but when fired properly have a lovely soft
lustre surface and are smooth to the touch. They are not meant to feel
like sand paper!

Let me know if you have had this problem and what conclusions you came

Phil Rogers.

Craig Martell on fri 21 jul 00

Hello Phil:

Tough questions. Best answered by someone who can also make a visual
inspection of the kiln and the ware. Language sometimes isn't
enough. I'll try to help a bit though.

Although you aren't seeing carbon inclusion in your trials perhaps they
aren't telling the full story. If you are pulling them from the spies in
the door they might be in the wrong location. I get much more carbon
inclusion in my salt kiln near the fireboxes. This will happen early on in
the firing before the refractories are heat saturated. Just before I go
into reduction between cone 08 and 06 I set the burners and damper for the
cleanest possible burn and let the kiln do it's work for about half an
hour. I still get a tad bit of carbon but it's not too bad.

I looked at the seger formula for your hi alumina slip. I don't know the
analyses of your ball clay and kaolin so I used the "ideal" analysis. It
shows a silica/alumina ratio of about 2.8 to 1. This is pretty low and one
would expect that this slip would resist a salt glaze. However, you say
that this slip has performed well in the past so, unless you've changed
materials or batches I wouldn't necessarily blame the slip. I've had a bit
of this dry area problem and what seems to rectify the situation is to slow
the draught in the kiln. When I salt, I turn the burners down to about
half their output and close the damper about half way and commence
salting. I put in about 3 to 4 pounds of salt at a time and keep the
burner/damper settings for about 10 to 15 minutes and watch the gasses at
the stack. I turn the burners back up and pull the damper out and regain
lost temperature and repeat the process until the trials show that I've put
in enough salt.

What made me think of this is the possibility of a strong flame path near
your fire box not allowing the salt to settle on the ware. The hi alumina
slips may need the extra vapor bathing to gain that smooth quality that you

hope this has helped some, Craig Martell in Oregon

Marcia Selsor on fri 9 mar 01

Janet Mansfield's Salt Glazed Ceramics is also a good one. I have both.
Jack's is about 10 years earlier.
Marcia in Montana

iandol wrote:
> Dear Karin Hurt
> Try putting "Jack Troy" into your Cyber search. He just about says it all. You could also try "Brongniart" if you read French. He first described a chemistry for the process
> Best regards,
> Ivor
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Marcia Selsor