Joy L. Holdread on thu 6 jun 02
My last kiln load had areas of serious warping and bloating.
I'm wondering if t faulty promoter contributed to an uneven temp raise in
the
bisque and the glaze load also. The bloating appeared in more than one clay
body but seemed prevalent in two areas of the kiln, I'm wondering if the
cause was temp speed problem in either the bisque, or glaze firing or kiln
loading? I have a gas A-1 kiln, three burners at the bottom. I used the
same size kiln shelves and one of the same stack combination I've used for
years.
Question
Can a bad bisque create bloating in the glaze firing?
Is there hope that if I fire the next glaze firing very slowly the
rest of the glazed pieces left over from that bisque will be OK.
I realize no one long distance can TELL me exactly what went wrong
I'm
looking for practical insights and experience.
Joy In Tucson Beautiful morning gonna be hot. I'm planning a temp shade
awning for the summer off the West back door of the studio. That forest
fire
on Mt. Lemon should be contained today.
e-mail mudnjoy@aol.com
web site http://holdreadstudios.hypermart.net/
See the famous studio dog "Shahaley" in sunglasses. This photo actually won
a pet of the week contest. How many people do you know who's dog treated
them to lunch at Steve's Sausage Deli?
http://hometown.aol.com/shahaleyk9/
Jon Pacini on thu 6 jun 02
Greetings All------Joy wrote---"My last kiln load had areas of serious
warping and bloating.------------------"
Bloating is the symptom exhibited by clay that has reached a temperature
where it is soft enough to allow gasses created by the volatilization of
trapped organics or carbon, to expand, but not allow them to be expelled.
These organics can be present in the raw clay or as carbon built up in
the clay during the bisque or early in the glaze firing by an excessive
reduction atmosphere.
Because of a too rapid or excessively reduced firing, these organics or
carbon, are not being properly volatilized before the body softens during
the high fire.
You can burn the organics out during the early stages of the glaze
firing by firing at a slow rate and with an oxidizing atmosphere. The hitch
is going to be if your glazes are starting to react with the clay body and
seal the organics in prior to them volatilizing. You could still end up with
some boating of the body or pin holing of the glaze.
If you can't rebisque the ware, which is the best solution, try to stay
under a temperature rise of 200*f an hr with an oxidizing atmosphere till
you pass your normal bisque temperature. Then proceed from that point as
normal.
Jon Pacini
Clay Manager
Laguna Clay Co
Ron Roy on thu 6 jun 02
Hi Joy,
Tell us about the clay - if it's got iron in it - and the iron got reduced
during the bisque - and the bloating happened in the thicker clay parts -
thats usually the way.
Slow the bisque firing from 500C (say 100C per hour) to the end and make
sure there is free oxygen and your burners are not reducing.
You can test for free oxygen with some combustable - like carboard or wood
- sticks - if it burns (flame) inside the kiln there is oxygen - if just
smoke then open your damper a bit and test again in 15 min.
>My last kiln load had areas of serious warping and bloating.
>I'm wondering if t faulty promoter contributed to an uneven temp raise in
the
>bisque and the glaze load also. The bloating appeared in more than one
clay
>body but seemed prevalent in two areas of the kiln, I'm wondering if the
>cause was temp speed problem in either the bisque, or glaze firing or kiln
>loading? I have a gas A-1 kiln, three burners at the bottom. I used the
>same size kiln shelves and one of the same stack combination I've used for
>years.
>Question
> Can a bad bisque create bloating in the glaze firing?
> Is there hope that if I fire the next glaze firing very slowly the
>rest of the glazed pieces left over from that bisque will be OK.
>
> I realize no one long distance can TELL me exactly what went wrong
I'm
>looking for practical insights and experience.
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