Naomi Rieder on sat 21 aug 99
I'm hoping that someone has had some experience in firing a "pit" built on
the ground out of bricks. In this case, the bricks are high-fire, the walls
are 2 bricks thick (no mortar), a floor of bricks, the inside dimensions are
4' x 4.5' and the wall height is about 40". Just fired for the first time
and had extreme breakage. The firing consisted of 5" of sawdust, then the
pots, then small pieces of redwood and cedar snuggly placed over the pots to
a height of about 15", then crumbled newspaper. Corrugated steel sheets were
set over 2/3 of the opening and the paper lit. After the fire spread, the
entire opening was covered with the sheets, but there were gaps.
The fire burned down after about 4-1/2 hrs. One pot near the windy end,
cracked within a very short time, but it was a surprise to find most of them
broken. The same, low-fire, bisqued, grogless clay successfully went
through a beach pit-firing, so I don't think it's the clay, but rather the
wood, ie., not enough, or, perhaps, it should have been hardwood for a slower
burning???
Much TIA.
Naomi
Vince Pitelka on sun 22 aug 99
Naomi -
>The fire burned down after about 4-1/2 hrs. One pot near the windy end,
>cracked within a very short time, but it was a surprise to find most of them
>broken. The same, low-fire, bisqued, grogless clay successfully went
>through a beach pit-firing, so I don't think it's the clay, but rather the
>wood, ie., not enough, or, perhaps, it should have been hardwood for a slower
>burning???
Naomi -
First, it is important to distinguish between a pit-firing and a sawdust
smoking. What you did was the latter, and it is not a true firing process,
because it does not achieve satisfactory temperatures for even minimal
sintering. It is a cosmetic technique, but one which is certainly capable
of giving very beautiful results to already bisque-fired work. It is the
nature of this process that as the sawdust smolders away, the wares are
heated very unevenly, and a low-thermal-shock body will be subject to high
failure rates. For higher thermal shock, you need either a very porous body
with lots of tempering materials (sand, grog, volcanic ash, etc.) or a
high-talc body, like the classic 50-50 talc/ball clay body.
One possible solution is to get a slower burn by slightly dampening your
sawdust. Generally, the coarser and dryer the sawdust, the faster and
hotter it will burn, while the finer and damper, the slower it will burn.
Of course, if it is too fine or too damp, it will not keep burning at all.
Also, the larger the work, the greater the chance that one part of a piece
will heat up considerably while another is stone cold, increasing the
chances of thermal shock damage.
If you suspect that the breakage is because of uneven heating, the above
tips should help. The other possibility is that some of the breakage occurs
when the pots settle upon one another during the burn. This problem can be
minimized by bedding the pots and sawdust with layers of chicken wire. The
chicken wire prevents the pots from settling directly against one another.
Usually, the chicken wire will stand up to a few "firings."
Good luck -
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801 ext. 111, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Naomi Rieder on mon 23 aug 99
Dear Vince:
Much thanks for your suggestions, especially dampening the sawdust. The clay
I use is a 50-50 talc/ball clay body, so I think the problem was not enough
wood, and not enough sawdust. And I only stacked ware once--that was enough
to know better!
Again, thank you. You are always there (on Clayart) with wonderful help.
Naomi
Antoinette Badenhorst on mon 23 aug 99
Naomi, This is my normal way of firing. You already got some wonderful
advise from previous writers. Don`t stack to many pots onto each other
if you do not use chicken wire.(I seldom stack more than 2 layers) The
openings in the bricks can be very small. Mix coarse and fine burning
material, no bigger than 2 cm in "chip" size. Make sure that your
bisque firing is not too high. Narrow opening pots,like bottles is a
better option. If you fire wider pieces, keep them in the middle. Place
the openings facing towards the center and make sure that you fill it
with some burning material. I fire over night but make sure that there
are no flames before I go to bed. Normaly the following morning there
are still some smoldering ashes.
Try another small bach and let us know!
Antoinette
--- Naomi Rieder wrote:
> ----------------------------Original
> message----------------------------
> I'm hoping that someone has had some experience in
> firing a "pit" built on
> the ground out of bricks. In this case, the bricks
> are high-fire, the walls
> are 2 bricks thick (no mortar), a floor of bricks,
> the inside dimensions are
> 4' x 4.5' and the wall height is about 40". Just
> fired for the first time
> and had extreme breakage. The firing consisted of
> 5" of sawdust, then the
> pots, then small pieces of redwood and cedar snuggly
> placed over the pots to
> a height of about 15", then crumbled newspaper.
> Corrugated steel sheets were
> set over 2/3 of the opening and the paper lit.
> After the fire spread, the
> entire opening was covered with the sheets, but
> there were gaps.
>
> The fire burned down after about 4-1/2 hrs. One pot
> near the windy end,
> cracked within a very short time, but it was a
> surprise to find most of them
> broken. The same, low-fire, bisqued, grogless clay
> successfully went
> through a beach pit-firing, so I don't think it's
> the clay, but rather the
> wood, ie., not enough, or, perhaps, it should have
> been hardwood for a slower
> burning???
>
> Much TIA.
>
> Naomi
>
===
Antoinette Badenhorst
PO Box 552
Saltillo,Mississippi
38866
Telephone (601) 869-1651
timakia@yahoo.com
__________________________________________________
Do You Yahoo!?
Bid and sell for free at http://auctions.yahoo.com
Gabrielle Madsen on sun 29 aug 99
gabriellemadse-@hotmail.com wrote: Dear Antoinette:
Your pit type kiln is perfect and the way you fired is to.
The problem IS the clay. You must use a high temp clay, or bisque your
pots much, much lower. The beach firing was a fluke, i'm sure that it
was
because the pot just didn't come into contact with the same heat shocks
that
are completely unavoidable in pit firings.
So, so hard to learn from our mistakes.
Been there, done that.
Good luck to you!
original article:http://www.egroups.com/group/clayart/?start=50518
> ----------------------------Original message-------------------------
---
> I'm hoping that someone has had some experience in firing a "pit"
built on
> the ground out of bricks. In this case, the bricks are high-fire,
the walls
> are 2 bricks thick (no mortar), a floor of bricks, the inside
dimensions are
> 4' x 4.5' and the wall height is about 40". Just fired for the first
time
> and had extreme breakage. The firing consisted of 5" of sawdust,
then the
> pots, then small pieces of redwood and cedar snuggly placed over the
pots to
> a height of about 15", then crumbled newspaper. Corrugated steel
sheets were
> set over 2/3 of the opening and the paper lit. After the fire
spread, the
> entire opening was covered with the sheets, but there were gaps.
>
> The fire burned down after about 4-1/2 hrs. One pot near the windy
end,
> cracked within a very short time, but it was a surprise to find most
of them
> broken. The same, low-fire, bisqued, grogless clay successfully went
> through a beach pit-firing, so I don't think it's the clay, but
rather the
> wood, ie., not enough, or, perhaps, it should have been hardwood for
a slower
> burning???
>
> Much TIA.
>
> Naomi
>
>
Antoinette Badenhorst on mon 30 aug 99
Gabrielle, somewhere there is a misunderstanding. I hope though that
your advise reach the right persons. I work in porcelain 6^10(a grolleg
or exell) and terracotta and I bisque at 1050C to get the best
strenth,color reaction and keep the shine (if I want to) I build with
common sement bricks create small openings to encourage the smoldering.
I cover with corrigated tin after a fire that I keep burning for 25
minutes.I fire over night. I use very fine as well as coarse sawdust
and I wet it if nessesary. Thank you though for the interest that you
have shown. Every one of us can ALWAYS learn from someone else.
Antoinette.
--- Gabrielle Madsen wrote:
> ----------------------------Original
> message----------------------------
> gabriellemadse-@hotmail.com wrote: Dear Antoinette:
>
> Your pit type kiln is perfect and the way you fired
> is to.
>
> The problem IS the clay. You must use a high temp
> clay, or bisque your
> pots much, much lower. The beach firing was a
> fluke, i'm sure that it
> was
> because the pot just didn't come into contact with
> the same heat shocks
> that
> are completely unavoidable in pit firings.
>
> So, so hard to learn from our mistakes.
>
> Been there, done that.
>
> Good luck to you!
> original
> article:http://www.egroups.com/group/clayart/?start=50518
> > ----------------------------Original
> message-------------------------
> ---
> > I'm hoping that someone has had some experience in
> firing a "pit"
> built on
> > the ground out of bricks. In this case, the
> bricks are high-fire,
> the walls
> > are 2 bricks thick (no mortar), a floor of bricks,
> the inside
> dimensions are
> > 4' x 4.5' and the wall height is about 40". Just
> fired for the first
> time
> > and had extreme breakage. The firing consisted of
> 5" of sawdust,
> then the
> > pots, then small pieces of redwood and cedar
> snuggly placed over the
> pots to
> > a height of about 15", then crumbled newspaper.
> Corrugated steel
> sheets were
> > set over 2/3 of the opening and the paper lit.
> After the fire
> spread, the
> > entire opening was covered with the sheets, but
> there were gaps.
> >
> > The fire burned down after about 4-1/2 hrs. One
> pot near the windy
> end,
> > cracked within a very short time, but it was a
> surprise to find most
> of them
> > broken. The same, low-fire, bisqued, grogless
> clay successfully went
> > through a beach pit-firing, so I don't think it's
> the clay, but
> rather the
> > wood, ie., not enough, or, perhaps, it should have
> been hardwood for
> a slower
> > burning???
> >
> > Much TIA.
> >
> > Naomi
> >
> >
>
===
Antoinette Badenhorst
PO Box 552
Saltillo,Mississippi
38866
Telephone (601) 869-1651
timakia@yahoo.com
__________________________________________________
Do You Yahoo!?
Bid and sell for free at http://auctions.yahoo.com
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