r horning on sun 28 sep 03
hello all,
I have been hesitant to ask for help as someone fairly new to the list but I have seen you be most gracious to those in need. I will greatly appreciate any suggestions as I learn my way in the process of salt firing.
i am currently firing my new (I've only fired it three times) salt kiln. In my last firing I introduced about 9 lbs of salt and saw very little effect. The kiln walls are primarily itc coated soft brick. It is a Minnesota flat top kiln, about 27 cubic feet. I understand that the early firings will need quite a bit of salt, as it will build up on the walls. I would like to increase the salt effect. As suggested in Jack Troys "Salt Glazed Ceramics" I am going to close the damper for a few minutes after each salt introduction to keep the vapours in the kiln.
The last time I fired I turned the burners down quite a bit and closed the damper after salting. A few minutes later I put the pyrometer in the kiln and discovered the temperature had rapidly dropped. I had a lot of pin-holing and even some bloating of the glazes, and thought it might have to do with this rapid temperature drop.
I don't know how to carefully monitor the temperature of the kiln so that it does not decrease too much when the damper is closed, without using a pyrometer. I am not experienced enough to see the difference in single cone increases or decreases of temperature. Will the pyrometer be harmed by the sodium vapours?
It is a "Fluke" brand pyrometer, with 1"ceramic sections of tubing over the metal.
I am also going to slow down the cooling process to see if this will help with the glaze problems. I am going to try backing the gas off once I reach temperature, cone 9, and let it go for an hour or so.
Thanks, Rebecca
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Paul Herman on sun 28 sep 03
Rebecca,
If your thermocouple is in a refractory tube, and protected from the
salt vapors, it should be OK.
Good firings,
Paul Herman
Great Basin Pottery
423-725 Scott Road
Doyle, California 96109 US
potter@psln.com
----------
>From: r horning
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: pyrometer in salt kiln
>Date: Sun, Sep 28, 2003, 10:22 AM
>
> Will the pyrometer be harmed by the sodium vapours?
> It is a "Fluke" brand pyrometer, with 1"ceramic sections of tubing over the
> metal.
Fredrick Paget on sun 28 sep 03
>
> Will the pyrometer be harmed by the sodium vapours?
>It is a "Fluke" brand pyrometer, with 1"ceramic sections of tubing
>over the metal.
>Thanks, Rebecca
>
You should make some expendable cover tubes out of porcelain or
stoneware that you can stick in the kiln and leave in place during
the whole firing.
Depending on what they are made of they will last a while and
protect the thermocouple.
Let us know how the soft brick kiln holds up. I have read in the
past that they go to ruin pretty fast in salt.
Fred
--
From Fred Paget, Marin County, California, USA
fredrick@well.com
iandol on mon 29 sep 03
Dear Rebecca Horning,
I do not think you need a pyrometer. Salt (Sodium Chloride) will attack =
and destroy the porcelain sheath.
May I suggest you close the damper and trim the heat imput before you =
add the salt. If you have a good high temperature as shown by your =
cones, somewhere between cone 8 and 12, you will get rapid decrepitation =
(explosion due to thermal shock) then fine, melting salt particles will =
not be swept from the kiln before they have had time to impinge on our =
clay. Yes, hold the damper in and let the salt have chance to work.
May I also suggest that you test some slip recipes, based on your body =
clay but with additions as separated tests of Silica, Potash Felspar and =
Ball clay. Try ball clay on its own as well.
I recall it is written that adding salt causes intense cooling but never =
found this to be so. But this could be a factor of kiln design through =
the choice of brick, RI bricks retaining less heat than dense firebrick =
which act as a heat ballast. Learn to read the Heat Colour of your kiln =
rather than relying on cones, which become unreliable once affected by =
salt, or the Pyrometer, for the reason given.=20
Wishing you every success,
Ivor Lewis. Redhill, South Australia
Vince Pitelka on tue 30 sep 03
Ivor wrote:
"I do not think you need a pyrometer. Salt (Sodium Chloride) will attack and
destroy the porcelain sheath."
Ivor -
A pyrometer is helpful in almost any kiln. In the US, many salt glaze
potters use pyrometers, with a porcelain sheath to protect the thermocouple.
It takes many many firings to destroy the sheath, and then you just install
another one. They are very easy to make, so it isn't a problem if they need
to be replaced frequently. If you use a 50/50 alumina/kaolin paste to seal
the sheath into the brick where it protrudes into the kiln, it is very easy
to remove when replacement is required.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Office - wpitelka@tntech.edu
615/597-6801 x111, FAX 615/597-6803
http://iweb.tntech.edu/wpitelka/
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