Suella on sat 10 nov 01
Hi
Does anyone have experience with bloating in a once-fired (no bisque =
firing) kiln? It has been suggested to me that the cause could be the =
early salting of the pots before the gases escape from the body. It's =
difficult for me to test the theory, as I only have 1 kiln. I would be =
interested to hear from anyone who knows or has experience of something =
similar.
Thanks
Allan P
Tony Ferguson on sat 10 nov 01
Allan,
I am not sure what you mean by a "once-fired kiln". If you are bloating,
you are more than likely firing too fast and or adding the salt to early.
Your salt should be added around cone 10 (when it starts to bend to half way
down might work well for you?) Ask people who salt. The earlier stages of
once firing are crucial that you go slow so the steam, organics can burn out
and escape. I single everything in either a gas or my anagama. You should
candle over night to dry out the phantoms, and then start increasing the
heat from morning to late evening. Example: glaze thursdays, load friday,
candle over night. Start turns ups or adding wood Saturday morning, If
it's a gas, you will be done by midnight (depends on the size), if its wood,
Sunday morning (this depends on how much ash you want as well, the
style/size of your kiln).
Some tips--Listen to the kiln, the sound of how the wood is buring (or gas
hissing)--regularily look at the atmosphere in the kiln and surface of your
pots. Now ask yourself, "if I was a pot, would I be ready to get a little
hotter?" he he. yes, I do this. Each firing is different because of the
multitude of variables, when you glazed, how thick the glaze was, outside
temp, humdity, etc, etc. Some people fire like science--others like art--I
combine the two.
KEEP A SCHEDULE to help guide you if need be. BUT, you should be able to
complete a firing within 24 hours in a gas kiln if you are reducing. IF you
are oxidizing, less of course. I have to remind myself when I want to rush:
Do you want all the work leading up to this last stretch to be for naught?
NO, I don't think so. I have ruined entire loads of pots because I rushed
(usually because I didn't know what the hell I was doing and thought I
did--but you got to start somewhere. I scraped a whole summer--bricks from
old kilns, abandoned chimmney stacks, people's pathways through their yard,
part of a dog kennel, brick from an abandoned steel mill, beehive brick with
a double taper I used for the arch (NOT RECOMMENDED). Just take more time,
like we should with most things in life. Anyway, if you have any more
questions, feel free to contact me.
Tony Ferguson, Duluth, MN
----- Original Message -----
From: "Suella"
To:
Sent: Friday, November 09, 2001 10:18 PM
Subject: salt/soda once-firing and bloating
Hi
Does anyone have experience with bloating in a once-fired (no bisque firing)
kiln? It has been suggested to me that the cause could be the early salting
of the pots before the gases escape from the body. It's difficult for me to
test the theory, as I only have 1 kiln. I would be interested to hear from
anyone who knows or has experience of something similar.
Thanks
Allan P
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Hank Murrow on sat 10 nov 01
>Hi
>
>Does anyone have experience with bloating in a once-fired (no bisque
>firing) kiln? It has been suggested to me that the cause could be the
>early salting of the pots before the gases escape from the body. It's
>difficult for me to test the theory, as I only have 1 kiln. I would be
>interested to hear from anyone who knows or has experience of something
>similar.
>
>Thanks
>
>Allan P
>
Dear Allan;
My experience was that slowing down the firing through the C/06
region will givee the combustibles a chance to escape the body before
glazing/vitrification seals them in.
Try slowing down and see what happens.
regards, Hank
vince pitelka on sat 10 nov 01
Does anyone have experience with bloating in a once-fired (no bisque firing)
kiln? It has been suggested to me that the cause could be the early salting
of the pots before the gases escape from the body. It's difficult for me to
test the theory, as I only have 1 kiln. I would be interested to hear from
anyone who knows or has experience of something similar.
Allan -
In my experience this is a consistent problem in salt once-firing, and as a
result we do not once-fire in salt. The residual salt in the firing seals
the surface of the body before outgassing is done, and thus the trapped
volatiles and the eventual bloating. Anyone out there who avoids this
problem in salt once-firing?
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
Steve Mills on sun 11 nov 01
In message , Suella writes
>Hi
>
>Does anyone have experience with bloating in a once-fired (no bisque =3D
>firing) kiln? It has been suggested to me that the cause could be the =3D
>early salting of the pots before the gases escape from the body. It's =3D
>difficult for me to test the theory, as I only have 1 kiln. I would be =3D
>interested to hear from anyone who knows or has experience of something =3D
>similar.
>
>Thanks
>
>Allan P
Personally, I very much doubt it. In our experience here with customer
problems, bloating is often caused by firing in a semi reducing
atmosphere during the early stages, this causes carbon to become trapped
in the body and expand into a gas at a later stage to cause the bloats.
We recommend that our customers ensure that there is plenty of free
oxygen coming into the kiln in the period between zero and 1,000 degrees
centigrade. In the case of electric kilns we recommend either propping
the lid lightly open, or if you have the good fortune to have a hole on
the lid leaving that unplugged until the same temperature.
Steve
Bath
UK
--
Steve Mills
Bath
UK
Ron Roy on wed 14 nov 01
Stephen Hill once fires and he stresses going through the mid stage in
firing - 600C to 900C slowley and with lots of oxygen - leave spys open -
to get rid of the combustables in the clay.
This can be problematic when firing to cone 6 - many cone 6 glazes have
boron which tends to seal over the clay before the crbon and sulfure are
out.
RR
>Does anyone have experience with bloating in a once-fired (no bisque
>firing) kiln? It has been suggested to me that the cause could be the
>early salting of the pots before the gases escape from the body. It's
>difficult for me to test the theory, as I only have 1 kiln. I would be
>interested to hear from anyone who knows or has experience of something
>similar.
>
>Thanks
>
>Allan P
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
Paul Taylor on wed 14 nov 01
Dear Alan
I used to raw glaze but I no longer do.
It had its advantages . There was always a felling of immediacy from the
raw glazing and the glaze seemed to flow better onto the raw pots - some how
more harmonious - less of a coating. There were less pots hanging about
waiting for me to remember what I intended to do with them. AND In pottery
conversations I could say " Actually I raw glaze" and bask in the reverence.
But there was enough lost pots - split rims - to pay for a biscuit .
There was the occasional bloat if I pushed the kiln too fast or made a
mistake with a burner setting - mostly all the lidded pots would bloat. The
firing was longer so I would get tired and impatient, at the end of a firing
when I needed to be at my most alert.
With biscuit firing you get two attempts at clearing the glaze of
carbon- the biscuit firing and the glaze firing. The iron and copper in my
glazes like to start their reduction early so it helps to be certain that
all the carbon is out by 900c . There is a seeming contradiction there, but
the carbon in the atmosphere does not seem to bloat the body while the stuff
in the pot does.
So sadly I can no longer boast - but I have less stress.
I know that 'probably' there is a clay and firing schedule that will
allow you to raw salt glaze, but it 'may' not give the colors and surface
you want . If you biscuit fire you can concentrate on the effects you want
and not have to make such compromise. You could have a long and expensive
search for the combination of clay recipe and firing schedule and still find
biscuit more economical in the long run - even if you have to build a cheap
biscuit kiln.
Regards from Paul Taylor
http://www.anu.ie/westportpottery
Alchemy is the proof that economics is not a science.
> Does anyone have experience with bloating in a once-fired (no bisque firing)
> kiln? It has been suggested to me that the cause could be the early salting
> of the pots before the gases escape from the body. It's difficult for me to
> test the theory, as I only have 1 kiln. I would be interested to hear from
> anyone who knows or has experience of something similar.
>
iandol on thu 15 nov 01
Dear Folks,
In reading responses to the Palmer's problem I keep getting the =
impression that many people are assuming that they are using =
conventional glazes during their firings. As I read it, they are not, =
though I know it is not unusual in modern studio practice to use a liner =
glaze and exploit the aesthetic effects of salt and soda firing on outer =
surfaces. For along time it was assumed that salting destroyed the =
integrity of conventional glazes so it was unusual to use the two =
processes together.
Traditionally, salt glaze was a once fired process. Any residual organic =
material, such as coal, lignite or shale oil from some of the clays =
which were used would have burnt, assisting the h eating process, long =
before the clay sintered. Firings were usually long affairs, upwards of =
a week from light up to cracking the seals. Much of the ware fired was =
more that half an inch thick, often of complex form and construction =
(think sewer traps, split gutters, sediment traps, sinks and the like). =
Heating was slow.
Best regards,
Ivor Lewis. Redhill, South Australia
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