Jim V Brooks on tue 2 apr 02
Actually i believe the reason for a shelf on the bottom of the kiln is to
catch any glaze pops.. runs, spills, and not let it get into the firebrick..
Anyone that has glaze run on soft brick knows how damaging it is.. A shelf
is easier to clean.. or can be discarded a lot cheaper than a kiln... Jim
in Denton
Carol Tripp on tue 2 apr 02
Arnold Howard wrote:
>Having an extra shelf on the bottom of the kiln is not always
>necessary. The extra thermal mass of the shelf can cause the bottom
>to fire cooler than the rest of the kiln.
Dear Arnold,
When would the extra shelf not be necessary? I have always read that one
should have a shelf on 1/2" props at the bottom of an electric kiln. Is this
just some old saw that everyone keeps repeating but no one ever questions?
Could you please elaborate?
Thanks and regards,
Carol
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Kathy Maves on tue 2 apr 02
Hi Carol and Arnold,
Envirovent recommends that you prop your first shelf
layer 1/2 or 1 inch from the floor of your electric
kiln to allow ventilation. Those three little holes in
the bottom have to be open and clear of junk for it to
work. There may very well be other reasons too.
Arnold, maybe you skip the whole first shelf
altogether for a bisque? I've seen people tumble stack
all their bisques, very pretty, tons of pots in the
kiln. I just don't have the guts for that. Are you
saying that you fire glazed pots on the kiln floor?
Thanks,
Kathy
kathymaves@yahoo.com
--- Carol Tripp wrote:
> Arnold Howard wrote:
> >Having an extra shelf on the bottom of the kiln is
> not always
> >necessary. The extra thermal mass of the shelf can
> cause the bottom
> >to fire cooler than the rest of the kiln.
>
> Dear Arnold,
> When would the extra shelf not be necessary? I have
> always read that one
> should have a shelf on 1/2" props at the bottom of
> an electric kiln. Is this
> just some old saw that everyone keeps repeating but
> no one ever questions?
> Could you please elaborate?
> Thanks and regards,
> Carol
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Snail Scott on tue 2 apr 02
At 05:25 AM 4/2/02 +0000, you wrote:
I always figured the shelf at the bottom was to
prevent wear and tear on the kiln floor. And if
you put it flat on the floor, you do distribute
the load more evenly, but the thermal mass of the
shelf sitting right on the IFB makes a cold spot,
for sure.
It still tends to be cold if you use short posts,
but less so.
I am reluctant to subject the floor of my poor old
kiln to the direct friction of my large work, but
I do it anyway when I need the space. And, I figure
the work itself actually is a better-distributed
load than having the whole weight of the piece on
four little posts! That's a lot of PSI!
-Snail
Ann Brink on tue 2 apr 02
I always thought that the extra bottom shelf helps a bit with slow cooling,
radiating heat. For that same reason, if I have space left at the top
(usually don't) I add a shelf, picturing it radiating heat downward, while
the IFBs wouldn't. ( I have a Skutt 1027, no vent or controller, but leave
top peep open the whole time)
Ann Brink in CA
> At 05:25 AM 4/2/02 +0000, you wrote:
>
> I always figured the shelf at the bottom was to
> prevent wear and tear on the kiln floor. And if
> you put it flat on the floor, you do distribute
> the load more evenly, but the thermal mass of the
> shelf sitting right on the IFB makes a cold spot,
> for sure.
>
> It still tends to be cold if you use short posts,
> but less so.
>
m markey on wed 3 apr 02
Hi Everybody!
I usually recommend a bottom kiln shelf, to protect the bottom of the kiln.
This is especially necessary if there are several users of the same kiln,
such as in a community college. Kiln shelves can always be rewashed, if a
little glaze drips on them, but a kiln bottom is not replaceable!
There are some electric kilns with elements on the bottom, too. They would
need that 1/2" to work effectively.
Best wishes!
Mohabee NakedClay@hotmail.com
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Arnold Howard on wed 3 apr 02
Kathy raised a good point about firing glazed ware on the kiln
bottom. I would not risk the bottom with glazed ware.
At Paragon, we recommend placing small pieces directly on the kiln
bottom.
Arnold Howard
Paragon
--- Kathy Maves wrote:
> Hi Carol and Arnold,
> Envirovent recommends that you prop your first shelf
> layer 1/2 or 1 inch from the floor of your electric
> kiln to allow ventilation. Those three little holes in
> the bottom have to be open and clear of junk for it to
> work. There may very well be other reasons too.
> Arnold, maybe you skip the whole first shelf
> altogether for a bisque? I've seen people tumble stack
> all their bisques, very pretty, tons of pots in the
> kiln. I just don't have the guts for that. Are you
> saying that you fire glazed pots on the kiln floor?
> Thanks,
> Kathy
> kathymaves@yahoo.com
> --- Carol Tripp wrote:
> > Arnold Howard wrote:
> > >Having an extra shelf on the bottom of the kiln is
> > not always
> > >necessary. The extra thermal mass of the shelf can
> > cause the bottom
> > >to fire cooler than the rest of the kiln.
> >
> > Dear Arnold,
> > When would the extra shelf not be necessary? I have
> > always read that one
> > should have a shelf on 1/2" props at the bottom of
> > an electric kiln. Is this
> > just some old saw that everyone keeps repeating but
> > no one ever questions?
> > Could you please elaborate?
> > Thanks and regards,
> > Carol
>
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Arnold Howard on wed 3 apr 02
Years ago it was a common belief that the kiln bottom remains
cooler because heat rises. Consequently, people placed a shelf in
the bottom of the kiln on short posts. This was to avoid
underfiring the ware on the kiln bottom.
In the mid-80s, I ran numerous tests on Paragon's first automatic
kiln. I carefully glued the witness cones to sheets of cardboard
and labeled them by shelf number, for every firing. (For years I
had boxes of test cones on file.)
I found that *both* the top and bottom of the kiln fired cooler
when ware was evenly distributed throughout the kiln. The center
fired hotter. So we adjusted the elements to fire cooler in the
center section.
The reason the top and bottom fired cooler than the center is that
the elements had to heat the lid and bottom in addition to the
ware. A kiln's lid and bottom are large thermal masses that absorb
heat.
People believed that the bottom fired cooler than the rest of the
kiln because their loads were uneven. Most people were loading more
ware in the bottom than the top. Areas of the kiln that are lightly
loaded get hotter.
You can fire ware directly on the kiln bottom provided you place
only small pieces there or use hotter elements in the bottom wall
section. If the ware underfires, you can place more ware in the
center section of the kiln. By redistributing thermal mass inside
the kiln, you change the heat distribution.
However, if you have fired the kiln successfully with a shelf 1/2"
from the kiln bottom, it may be best to leave well enough alone.
Arnold Howard
Paragon
--- Carol Tripp wrote:
> Arnold Howard wrote:
> >Having an extra shelf on the bottom of the kiln is not always
> >necessary. The extra thermal mass of the shelf can cause the
> bottom
> >to fire cooler than the rest of the kiln.
>
> Dear Arnold,
> When would the extra shelf not be necessary? I have always read
> that one
> should have a shelf on 1/2" props at the bottom of an electric
> kiln. Is this
> just some old saw that everyone keeps repeating but no one ever
> questions?
> Could you please elaborate?
> Thanks and regards,
> Carol
>
>
> _________________________________________________________________
> Join the world’s largest e-mail service with MSN Hotmail.
> http://www.hotmail.com
>
>
______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your
> subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
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Craig Clark on wed 3 apr 02
Arnold, would the use of a layer of high temp (2700 F) insulating
blanket lining the inside of the bottom and one lining the underside of the
lid take care of the thermal mass difficulty?
Craig Dunn Clark
619 East 11 1/2 st
Houston, Texas 77008
(713)861-2083
mudman@hal-pc.org
----- Original Message -----
From: "Arnold Howard"
To:
Sent: Wednesday, April 03, 2002 10:55 AM
Subject: Re: Need shelf 1/2" off kiln bottom?
> Years ago it was a common belief that the kiln bottom remains
> cooler because heat rises. Consequently, people placed a shelf in
> the bottom of the kiln on short posts. This was to avoid
> underfiring the ware on the kiln bottom.
>
> In the mid-80s, I ran numerous tests on Paragon's first automatic
> kiln. I carefully glued the witness cones to sheets of cardboard
> and labeled them by shelf number, for every firing. (For years I
> had boxes of test cones on file.)
>
> I found that *both* the top and bottom of the kiln fired cooler
> when ware was evenly distributed throughout the kiln. The center
> fired hotter. So we adjusted the elements to fire cooler in the
> center section.
>
> The reason the top and bottom fired cooler than the center is that
> the elements had to heat the lid and bottom in addition to the
> ware. A kiln's lid and bottom are large thermal masses that absorb
> heat.
>
> People believed that the bottom fired cooler than the rest of the
> kiln because their loads were uneven. Most people were loading more
> ware in the bottom than the top. Areas of the kiln that are lightly
> loaded get hotter.
>
> You can fire ware directly on the kiln bottom provided you place
> only small pieces there or use hotter elements in the bottom wall
> section. If the ware underfires, you can place more ware in the
> center section of the kiln. By redistributing thermal mass inside
> the kiln, you change the heat distribution.
>
> However, if you have fired the kiln successfully with a shelf 1/2"
> from the kiln bottom, it may be best to leave well enough alone.
>
> Arnold Howard
> Paragon
>
>
>
>
>
>
> --- Carol Tripp wrote:
> > Arnold Howard wrote:
> > >Having an extra shelf on the bottom of the kiln is not always
> > >necessary. The extra thermal mass of the shelf can cause the
> > bottom
> > >to fire cooler than the rest of the kiln.
> >
> > Dear Arnold,
> > When would the extra shelf not be necessary? I have always read
> > that one
> > should have a shelf on 1/2" props at the bottom of an electric
> > kiln. Is this
> > just some old saw that everyone keeps repeating but no one ever
> > questions?
> > Could you please elaborate?
> > Thanks and regards,
> > Carol
> >
> >
> > _________________________________________________________________
> > Join the world's largest e-mail service with MSN Hotmail.
> > http://www.hotmail.com
> >
> >
>
____________________________________________________________________________
__
> > Send postings to clayart@lsv.ceramics.org
> >
> > You may look at the archives for the list or change your
> > subscription
> > settings from http://www.ceramics.org/clayart/
> >
> > Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
>
> __________________________________________________
> Do You Yahoo!?
> Yahoo! Tax Center - online filing with TurboTax
> http://taxes.yahoo.com/
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
John Forstall on wed 3 apr 02
I've been firing once a week for last 6 years with ware directly on the
floor of IFB. The first shelf sits on 4" high posts and fires to large cone
6. On IFB floor large cone indicates about 5-1/2. Early test showed cold
bottom with shelf sitting on kiln floor. I use largest diameter 4" post I
can find because whole kiln load is bearing directly on IFB. Used to worry
about it quite a bit, but nothing has ever happened. Every situation is
different. Testing is the only way. Nothing destroys theory quicker than
variables.
John Forstall
In Pensacola FL.
Arnold Howard on wed 3 apr 02
--- Craig Clark wrote:
> Arnold, would the use of a layer of high temp (2700 F)
> insulating
> blanket lining the inside of the bottom and one lining the
> underside of the
> lid take care of the thermal mass difficulty?
> Craig Dunn Clark
> 619 East 11 1/2 st
> Houston, Texas 77008
> (713)861-2083
> mudman@hal-pc.org
I've never tried that. I don't think you would see much of an
effect. But it would be an interesting experiment.
Arnold Howard
Paragon
>
> ----- Original Message -----
> From: "Arnold Howard"
> To:
> Sent: Wednesday, April 03, 2002 10:55 AM
> Subject: Re: Need shelf 1/2" off kiln bottom?
>
>
> > Years ago it was a common belief that the kiln bottom remains
> > cooler because heat rises. Consequently, people placed a shelf
> in
> > the bottom of the kiln on short posts. This was to avoid
> > underfiring the ware on the kiln bottom.
> >
> > In the mid-80s, I ran numerous tests on Paragon's first
> automatic
> > kiln. I carefully glued the witness cones to sheets of
> cardboard
> > and labeled them by shelf number, for every firing. (For years
> I
> > had boxes of test cones on file.)
> >
> > I found that *both* the top and bottom of the kiln fired cooler
> > when ware was evenly distributed throughout the kiln. The
> center
> > fired hotter. So we adjusted the elements to fire cooler in the
> > center section.
> >
> > The reason the top and bottom fired cooler than the center is
> that
> > the elements had to heat the lid and bottom in addition to the
> > ware. A kiln's lid and bottom are large thermal masses that
> absorb
> > heat.
> >
> > People believed that the bottom fired cooler than the rest of
> the
> > kiln because their loads were uneven. Most people were loading
> more
> > ware in the bottom than the top. Areas of the kiln that are
> lightly
> > loaded get hotter.
> >
> > You can fire ware directly on the kiln bottom provided you
> place
> > only small pieces there or use hotter elements in the bottom
> wall
> > section. If the ware underfires, you can place more ware in the
> > center section of the kiln. By redistributing thermal mass
> inside
> > the kiln, you change the heat distribution.
> >
> > However, if you have fired the kiln successfully with a shelf
> 1/2"
> > from the kiln bottom, it may be best to leave well enough
> alone.
> >
> > Arnold Howard
> > Paragon
> >
> >
> >
> >
> >
> >
> > --- Carol Tripp wrote:
> > > Arnold Howard wrote:
> > > >Having an extra shelf on the bottom of the kiln is not
> always
> > > >necessary. The extra thermal mass of the shelf can cause the
> > > bottom
> > > >to fire cooler than the rest of the kiln.
> > >
> > > Dear Arnold,
> > > When would the extra shelf not be necessary? I have always
> read
> > > that one
> > > should have a shelf on 1/2" props at the bottom of an
> electric
> > > kiln. Is this
> > > just some old saw that everyone keeps repeating but no one
> ever
> > > questions?
> > > Could you please elaborate?
> > > Thanks and regards,
> > > Carol
> > >
> > >
> > >
> _________________________________________________________________
> > > Join the world's largest e-mail service with MSN Hotmail.
> > > http://www.hotmail.com
> > >
> > >
> >
>
____________________________________________________________________________
> __
> > > Send postings to clayart@lsv.ceramics.org
> > >
> > > You may look at the archives for the list or change your
> > > subscription
> > > settings from http://www.ceramics.org/clayart/
> > >
> > > Moderator of the list is Mel Jacobson who may be reached at
> > melpots@pclink.com.
> >
> >
> > __________________________________________________
> > Do You Yahoo!?
> > Yahoo! Tax Center - online filing with TurboTax
> > http://taxes.yahoo.com/
> >
> >
>
____________________________________________________________________________
> __
> > Send postings to clayart@lsv.ceramics.org
> >
> > You may look at the archives for the list or change your
> subscription
> > settings from http://www.ceramics.org/clayart/
> >
> > Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
>
______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your
> subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
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Carol Tripp on thu 4 apr 02
Jim wrote:
> Actually i believe the reason for a shelf on the bottom of the kiln is
>to
>catch any glaze pops.. runs, spills, and not let it get into the
>firebrick..
>Anyone that has glaze run on soft brick knows how damaging it is.. A shelf
>is easier to clean.. or can be discarded a lot cheaper than a kiln...
>Jim
>in Denton
Why not fire on "pancakes" if you have a potentional dripper? I fire all my
test tiles on pancakes because one never knows. Anyway, I think I will try
this idea of Arnold's; fire small pieces directly on the bottom and combine
it with John's method of using wide diameter posts to support the shelves
above.
Regards,
Carol
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