Mary Driever on sun 16 nov 08
Just got a new kiln I am just learning to fire and I screwed up my first
load of porcelain it was cone 6 molded from slip I put in cone 6 in the setter
it went for eight and a half hours couldn't wait to get it all out and my
pieces are full of pimples. it bubbled, there was no glaze I used a prop for
the doll bust and it didn't even hold, that sagged and the poor babe has
pimples all over. I think I got too hot but I don't know what else, I did not
use the witness etc cones the kiln is so small that I can hardly get the
small stuff in let alone the large cones. This is a real small kiln got it just
for buttons and beads but I can't have this happen all the time.
Marya
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Lynn Goodman Porcelain Pottery on sun 16 nov 08
Hi Mary,
You need to find a way to squeeze in the witness cone-- it sounds
like you definitely overfired.
Lynn
On Nov 16, 2008, at 2:43 AM, Mary Driever wrote:
> Just got a new kiln I am just learning to fire and I screwed up my
> first
> load of porcelain
>
Lynn Goodman
Fine Porcelain Pottery
Cell 347-526-9805
www.lynngoodmanporcelain.com
William & Susan Schran User on sun 16 nov 08
On 11/16/08 2:43 AM, "Mary Driever" wrote:
> Just got a new kiln I am just learning to fire and I screwed up my first
> load of porcelain it was cone 6 molded from slip I put in cone 6 in the
> setter
> it went for eight and a half hours couldn't wait to get it all out and my
> pieces are full of pimples. it bubbled, there was no glaze I used a prop
> for
> the doll bust and it didn't even hold, that sagged and the poor babe has
> pimples all over. I think I got too hot but I don't know what else, I did
> not
> use the witness etc cones the kiln is so small that I can hardly get the
> small stuff in let alone the large cones.
Relying on Kilnsitter or pyrometer just will not provide information you
need for firing, you do need to make room for witness cones to be able to
see the work-heat.
Bill
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
Snail Scott on sun 16 nov 08
On Nov 16, 2008, at 1:43 AM, Mary Driever wrote:
> Just got a new kiln I am just learning to fire and I screwed up my
> first
> load of porcelain it was cone 6 molded from slip I put in cone 6 in
> the setter
> it went for eight and a half hours couldn't wait to get it all out and
> my
> pieces are full of pimples...
It does sound like overfiring was the basic problem.
Even if you have to do something weird to get a witness
cone in the kiln, you MUST do it, especially at first while
you are still calibrating your kiln sitter. Later, you can
probably do it only for occasional firings, but you must
do it now. Consider making some smaller, simpler work
for your first few firings, both to leave room for the witness
cones and to lessen the loss if things don't work out well.
It's best to be able to see the witness cone through a
peephole, so you can fire based on what you see and
shut it off when the cone bends. If you really can't fit the
cone in front of a peephole, though, put it in somewhere.
You can check after the firing to correlate the sitter's
results with the witness cone. Remember, the cone
doesn't have to sit on a shelf. It can be on top of something
unglazed, if you make a little clay shelf for the melted cone
to fall against (so it won't stick to the work). You can make a
little 'bridge' to set the cone on so that it can sit above lower
work even if the work is glazed. There's gotta be a way to
get a cone in there.
If you really can't fit one in, calibrate with witness cones
fired amongst smaller stuff, prior to firing the (relatively)
large stuff without cones. (If necessary, fire empty at first,
with nothing except the cones.) And, make sure you do a
firing with witness cones every dozen firings or so
thereafter, just to keep an eye on things. The cost of
cones and an extra firing now and then is a smaller
price to pay than ruined work and wasted effort.
-Snail
Steve Slatin on sun 16 nov 08
Mary -- you inadvertently showed why you should
never fire without at least one set of cones ...
if something goes wrong, you have no way to
immediately identify what happened.
It could have been a temperature issue; it
could have been the way the slip was mixed or
(if there was anything new in the ingredients)
a variation in raw materials.
Don't drive yourself crazy -- put whatever
kiln furniture you'd normally use in the
kiln, a set of cones, and fire it -- then
you'll know what happened.
And even if there's not enough space for a
cone pack in a loaded kiln, you'll probably
have to make space sufficient at least for
the cone for the target temperature for each
firing. That way, when something goes wrong
you'll have a clue about what happened.
Best wishes -- Steve S
--- On Sat, 11/15/08, Mary Driever wrote:
> Just got a new kiln I am just learning to fire and I screwed
> up my first
> load of porcelain it was cone 6 molded from slip I put in
> cone 6 in the setter
> it went for eight and a half hours couldn't wait to get
> it all out and my
> pieces are full of pimples. it bubbled, there was no
> glaze I used a prop for
> the doll bust and it didn't even hold, that sagged and
> the poor babe has
> pimples all over. I think I got too hot but I don't
> know what else, I did not
> use the witness etc cones the kiln is so small that I can
> hardly get the
> small stuff in let alone the large cones. This is a real
> small kiln got it just
> for buttons and beads but I can't have this happen
> all the time.
>
> Marya
> **************You Rock! One month of free movies delivered
> by mail from
> blockbuster.com
> (http://pr.atwola.com/promoclk/100000075x1212639737x1200784900/aol?redir=https://www.blockbuster.com/signup/y/reg/p.26978/r.email_footer)
Tony Ferguson on sun 16 nov 08
Mary,
It sounds like it fired to fast and the gases and or organics did not have enough time to burn out. Does your kiln have a program allowing you to ramp/adjust the rise in temperature rate of the kiln? You can program it to move slower through the burning out organics stage of the firing and allow time for the gas to get out. Once you hit red heat, you can go faster. Try lengthening your firing to about 10 hours--a bit slower in the initial stages.
Tony Ferguson
Mary Driever wrote: Just got a new kiln I am just learning to fire and I screwed up my first
load of porcelain it was cone 6 molded from slip I put in cone 6 in the setter
it went for eight and a half hours couldn't wait to get it all out and my
pieces are full of pimples. it bubbled, there was no glaze I used a prop for
the doll bust and it didn't even hold, that sagged and the poor babe has
pimples all over. I think I got too hot but I don't know what else, I did not
use the witness etc cones the kiln is so small that I can hardly get the
small stuff in let alone the large cones. This is a real small kiln got it just
for buttons and beads but I can't have this happen all the time.
Marya
**************You Rock! One month of free movies delivered by mail from
blockbuster.com
(http://pr.atwola.com/promoclk/100000075x1212639737x1200784900/aol?redir=https://www.blockbuster.com/signup/y/reg/p.26978/r.email_footer)
Take Care,
Tony Ferguson
Artist...Clay, Web, Photo, Video
...where the sky meets the lake...
http://www.tonyferguson.net
John Rodgers on sun 16 nov 08
Mary,
I fired slip cast porcelain for years, so have a few comments. BTW, you
didn't mention what porcelain slip you were using.
Don't know what kind of kiln you got, and it sounds like strictly manual
- no computer - but with a kiln sitter. If so, to know your kiln is
the first step - and you simply must run a test fire using witness cones
sitting on a shelf in the kiln along with the small cone in the kiln
sitter. You need three witness cones on the shelf - a 5, 6, and 7. You
also need a test piece of porcelain to fire at the same time. This will
tell you how your kiln is firing - cool, on temp, or to hot. Ideally
that #6 cone should be bent so the tip almost or just barely touches the
shelf. #5 cone should be laid out pretty flat, and the #7 cone just
beginning to bend. You may find that the miniature cone trips the kiln
just on the cool side. In any case, these four cones and their
relationship when the firing is done, will tell you a lot about how your
kiln is firing. If the cones are correct - meaning the temperatures are
correct, then move your thoughts to the porcelain. What did it do? Did
it still dimple. Did it still sag? Dimpling could be - and most likely
is - the result of contaminants in the porcelain. itself. Slip cast
porcelain is notorious for sagging. A lot depends on the form of the
piece to be fired. Often such pieces can be propped, using Prop-it or
other supporting materials. Sometimes you must make porcelain support
cones , that are tall enough to reach almost but not quite to the
touching point and then fill the gap with prop-it or other material. But
it all must shrink at the same time or sagging, bending, warping or
cracking or all of the above may occur.
You may have to test two or three times, but it is essential to know
your kiln. Once ou do, you can tell real quick if there are temperature
problems or clay problems.
Good luck with your projects.
Regards,
John Rodgers
Chelsea, AL
Mary Driever wrote:
> Just got a new kiln I am just learning to fire and I screwed up my first
> load of porcelain it was cone 6 molded from slip I put in cone 6 in the setter
> it went for eight and a half hours couldn't wait to get it all out and my
> pieces are full of pimples. it bubbled, there was no glaze I used a prop for
> the doll bust and it didn't even hold, that sagged and the poor babe has
> pimples all over. I think I got too hot but I don't know what else, I did not
> use the witness etc cones the kiln is so small that I can hardly get the
> small stuff in let alone the large cones. This is a real small kiln got it just
> for buttons and beads but I can't have this happen all the time.
>
> Marya
> **************You Rock! One month of free movies delivered by mail from
> blockbuster.com
> (http://pr.atwola.com/promoclk/100000075x1212639737x1200784900/aol?redir=https://www.blockbuster.com/signup/y/reg/p.26978/r.email_footer)
>
>
>
Antoinette Badenhorst on mon 17 nov 08
Mary I have 2 remarks to make. How full was your kiln. A very packed kiln fires differently from a loosely packed kiln. Also; was this the very first firing with this kiln or did you do a test firing with an empty kiln as many kiln instructions suggest?
--
Antoinette Badenhorst
www.clayandcanvas.com
www.studiopottery.co.uk
-------------- Original message ----------------------
From: Mary Driever
> Just got a new kiln I am just learning to fire and I screwed up my first
> load of porcelain it was cone 6 molded from slip I put in cone 6 in the setter
> it went for eight and a half hours couldn't wait to get it all out and my
> pieces are full of pimples. it bubbled, there was no glaze I used a prop for
> the doll bust and it didn't even hold, that sagged and the poor babe has
> pimples all over. I think I got too hot but I don't know what else, I did
> not
> use the witness etc cones the kiln is so small that I can hardly get the
> small stuff in let alone the large cones. This is a real small kiln got it
> just
> for buttons and beads but I can't have this happen all the time.
>
> Marya
> **************You Rock! One month of free movies delivered by mail from
> blockbuster.com
> (http://pr.atwola.com/promoclk/100000075x1212639737x1200784900/aol?redir=https:/
> /www.blockbuster.com/signup/y/reg/p.26978/r.email_footer)
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