[Clayart] Kiln issue

[Teri Lee via Clayart]

I have a firing issue that's left me scratching my head.

I have a secondhand 1976 Duncan kiln that uses small firing cones that,
when melted (temperature and time), shuts off the kiln--it's completely
non-automatic. I only use the kiln to bisque to Cone 06. I also always make
packs of witness cones: 07, 06, and 05 and I put a pack on each shelf, and
I usually use 2-3 shelves.

Here's the head-scratcher. Although the firing cone reliably melts and
shuts off the kiln at Cone 06, the witness cones don't go anywhere near 06.
On the top shelf (which sits higher than where the firing cone and tube
assembly sits), Cone 07 barely droops in the cone pack. On the bottom shelf
(lower than where the firing cone and tube assembly sits, natch), none of
the witness cones droop at all. The witness cones were all set at an angle
so that shouldn't be the problem.

Any ideas why I can't reach Cone 06 temperature? I know that the top of a
kiln tends to fire hotter than the bottom but even when I try to adjust the
dials to make the bottom hotter, I'm not reaching temp.

Thanks,
Teri Lee

P.S. I'm usually a lurker but occasionally I pop out a question and you all
have been great in helping me find answers! Clayart rocks.
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[Bonnie D. Hellman via Clayart]

You'll probably get a lot of replies, but I was told that cones are
formulated to fire standing upright. When they're used in a kiln sitter,
you need to use 1 kiln hotter to get the same results as a cone standing up.

So for a cone 06 firing, you should put a cone 05 in the sitter.

I've also found that you have a bit of leeway in HOW you position the
cones in the sitter. You can place them so the fatter end is on the
sitter, or so the skinnier end is more on the sitter, or the cone can be
centered. I'm no sure how much difference this makes, but since I only
use my cones as a "fail safe" since I have a wall mounted computer
controller, which I use for a pre-set bisque program at medium speed.

I fire my bisque to ^04, and use a ^03 in the sitter.

Also, since you know that a cone 06 doesn't get your firing to cone 06,
you might want to try your next firing using a cone 05, and if that is
still too cool, you can use a cone 04.

Many people bisque to a variety of temperatures, anywhere between ^08
and ^04 and probably warmer and cooler than that. You'll probably hear
from some of those people! <G>

Bonnie

Bonnie Hellman
Ouray, CO USA

[L TURNER via Clayart]

On Wed, Apr 20, 2016 at 3:35 PM, Teri Lee wrote:

>
> Here's the head-scratcher. ...

> shuts off the kiln at Cone 06, the witness cones don't go anywhere near 06.
> On the top shelf (which sits higher than where the firing cone and tube
> assembly sits), Cone 07 barely droops in the cone pack. On the bottom shelf

> ...none of the witness cones droop at all. ...

> Any ideas why I can't reach Cone 06 temperature?

I have a small doll kiln I use for tests and general "tinkering." It is
about nine inches by 5 inches by 9 inches tall and has a kiln sitter
controller. I have also have observed that the kiln sitter always trips
before the cone on the shelf of the same number as in the sitter starts to
bend. I just accept that the kiln sitter is warmer than the shelves and I
use a higher cone in the sitter than the target cone on the shelf.

Why this happens?

My speculation is that the heat transfer to the kiln setter is better than
to the kiln shelf area because of the "view factor",
the emissivity of the kiln sitter is higher,
and
perhaps most importantly,
the thermal mass of the sitter-cone assembly is significantly smaller than
the shelf-cone-pack assembly.

Put another way, it takes longer for an iceberg to melt than an ice-cube
even when in the same sauna.


LT
The Woodlands, TX

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[Tommy Humphries via Clayart]

Hello,

Small cones are reliably bad in the kiln sitter. Cones are made to be fired standing up at a preset angle. You get more reliable results using the square bars made specifically for this use. Also, you need periodic calibration on the kiln sitter. When new the sitter comes with a gauge that lets you adjust the drop point on the actuation rod. I think orton will send you one, with instructions for use upon request.

The large standing cones are your sure bet when it comes to firing your kiln accurately. However, make sure you have current production run cones. If they are different colors on each temp you are good to go, but if they are all white, or all brown ( for lower temps) they are OLD, and do not match current cone charts. I have seen nearly 1-1/2 cone difference in old and new ^6.

I was once told that the taper of the cones was to gauge differing thicknesses of pots. As the tip bends past the area of the cone that matches the thickness of your pot, then the pot is fired to that cone... Anyone know if this is accurate?

Tommy Humphries

Sent from my iPad

[William Schran via Clayart]

As others have written, best to use the bars instead of small cones for
the Kilnsitter.
You should use one or two cones hotter in the Kilnsitter, so cone 04 in
sitter for cone 06 firing.

But more importantly, the Kilnsitter must be kept in adjustment.
You can find the adjustment gauge and instructions online.
And even more importantly, you really should use the Kilnsitter as a
back-up device.
Firing by large witness cones is much more accurate way to fire.

Bill

Bill Schran
www.creativecreekartisans.com
wsc...@cox.net



On 4/20/16, 4:35 PM, "Clayart on behalf of Teri Lee via Clayart"
<clayart...@lists.clayartworld.com on behalf of

[Ken Chase via Clayart]

Tommy:
As I'm firing my first kiln for the first time tomorrow I'm not
Clear on whether to set for 04 or 06. Some of the pieces I need
To bisque are chucks and rather thick. Will that be a factor?
I ask because the first time I brought wares to a local studio for
Firing I was told one of my pots was too thick and required it
To be bisque fired a second time. Also, the kiln is automatic so
I assume no need to use cones? And finally.. Do I mix the kiln
Wash with water till a paste consistency.
Thanks
Ken Chase

Sent from my iPad

[Arnold Howard via Clayart]

On 4/20/2016 5:42 PM, Bonnie D. Hellman via Clayart wrote:
> You'll probably get a lot of replies, but I was told that cones are
> formulated to fire standing upright. When they're used in a kiln sitter,
> you need to use 1 kiln hotter to get the same results as a cone standing
> up.
>
> So for a cone 06 firing, you should put a cone 05 in the sitter.

I agree with Bonnie. Place a hotter cone in the Kiln Sitter. Use
whatever small cone number is required to make the correct witness cone
bend on the shelves. Before you begin experimenting with cone numbers,
calibrate the Kiln Sitter.

The Kiln Sitter is a pretty amazing, reliable shut-off. It makes a good
safety backup on digital kilns, too.

Sincerely,

Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
aho...@paragonweb.com / www.paragonweb.com

[Arnold Howard via Clayart]

On 4/20/2016 3:35 PM, Teri Lee via Clayart wrote:
I know that the top of a
> kiln tends to fire hotter than the bottom but even when I try to adjust the
> dials to make the bottom hotter, I'm not reaching temp.

The bottom is difficult to heat, because the thermal mass of the
firebrick bottom absorbs a lot of energy. The top in many kilns is
difficult to heat for the same reason--the lid absorbs a lot of energy.
You can compensate for this by placing lighter, smaller pieces in the
area of your kiln that is difficult to heat.

Sincerely,

Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
aho...@paragonweb.com / www.paragonweb.com

[Paul Gerhold via Clayart]

Or you can adjust the kiln setter to fire in such a way that the cone in the setter exactly matches the witness cone. You Can do this by adding a small amount of weight to the claw such that the small cone in the sitter has less pressure on it so it bends at a higher temp. I have three electric kilns and this keeps me from having to remember the firing differences between the kilns. Best to do this at glaze cone since bisque is more tolerant of firing discrepancies.

Paul

.

Sent from my iPad

[Ken Chase via Clayart]

Bill:
As my kiln is electronic and has no kiln sitter how should I use cone
To assure the kiln is reaching the correct temps? My takeaway
From some of the post is that checking is a good idea.
Thanks
Ken

Sent from my iPad

[William Schran via Clayart]

Ken,
You should get in the habit of using witness cones in EVERY firing right
from the git go.
They are to most accurate way to measure work heat - what truly happened
in the firing.
Does not matter - manual or automatic kiln - use witness cones.
Even if you set the controller to fire a fast or slow bisque, the
controller is controlled by the thermocouple.
Type ³K² thermocouples (what you most likely have) are known to be
inaccurate above 2000F.
So even if you are using a preset program, always use witness cones.
A three pack is best - for cone 06 firing use cones 07, 06, 05 in the cone
pack and put one pack on bottom and one on top.

Bill

Bill Schran
www.creativecreekartisans.com
wsc...@cox.net

On 4/21/16, 9:16 AM, "Clayart on behalf of Ken Chase via Clayart"

<clayart...@lists.clayartworld.com on behalf of
cla...@lists.clayartworld.com> wrote:

[David Woof via Clayart]

Hi everyone,
Regrets that Lately i have limited time to read everyone's posts, so here goes with apologies if someone also posted this:

On my older manual kilns I lay down a refractory blanket on the kiln floor as there is no need to allow heat to penetrate and escape thru the floor brick. From this point it depends on what sort (volume vs mass) of ware one places in the bottom stacking to absorb the heat in situ, or allow it to rise.

In other pre computor applications;
Where I wish to absorb heat to slow the rise during the beginning of the firing, I place
older(degenerated) shelves as hearth plates upon which I place the short
posts that support the first ware supporting shelves.
Eventually during the firing, as the kiln evens out in upper regions, this absorbed heat at the bottom is released and can contribute to even out a finicky bottom. Depending of course on what one stacks there in anticipation of a considered effect.

As Arnold brings out; judiciously placing less or more mass where it can effect heat absorption and heat rise will give one much control in getting the even firings we desire.

One must not confuse mass with volume vs empty space...... Gotta think this thru, and though it is not "rocket science" there are physical laws to understand and apply.

Ceramic resists absorbing heat when first applied but holds heat for longer durations after being absorbed, so duration of the fireing can mean much when planning firing stacking and mapping of a kilns performance.

Vital to do!!! Check with kiln manufacturer before adding refractory insulation to the kiln lid.

Idea number 578: Do without pizza, beer, and impulse spending for six months, save the bucks, and buy a computerized kiln with the "Zone Control" feature.

My computerized kiln will sit there happily maintaining within one degree f on all three zones from start up to firing finish and what ever cool down protocol is chosen.

David
***************************************************

> To: cla...@lists.clayartworld.com
> Date: Thu, 21 Apr 2016 08:39:26 -0500
> Subject: Re: [Clayart] Kiln issue
> From: cla...@lists.clayartworld.com
> CC: aho...@paragonweb.com

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[Paul Gerhold via Clayart]

Actually doubt ceramic resists absorbing heat. Laws of heat transfer apply pretty much uniformly to all materials.

Paul

Sent from my iPad

> On Apr 21, 2016, at 6:56 PM, David Woof via Clayart <cla...@lists.clayartworld.com> wrote:
>
> Ceramic resists absorbing heat when first applied but holds heat for longer durations after being absorbed, so duration of the fireing can mean much when planning firing stacking and mapping of a kilns performance

[Ken Chase via Clayart]

Forgive me another naive question. What is a refractory blanket?
And the fellow who sold me the kiln suggested I place a shelf on the
Bottom of the kiln, on a short post, or direct. Is that to protect against
Runny glaze? Or is there another reason. And finally. When I mix kiln wash should it only be for that application or would I mix a large
Batch and keep in a gallon container.
Thanks to all who have indulged my rookie questions. My first kiln
Did not come without some anxiety as I've never done this before.
Best
Ken

Sent from my iPad

[Tommy Humphries via Clayart]

The kiln shel on or at the bottom of the kiln is purely to protect the bricks from wear and tear. The blanket is kaowool, preferably 1" thick, for added insulation.

As for the kiln wash, if it is a premixed store bought I would mix just enough for the job, as some washes can settle out like concrete in the bottom of the container.

Tommy Humphries

Sent from my iPad

[William Schran via Clayart]

Ken,
The bottom shelf is primarily to protect the floor of the kiln, but using
a shelf with 1² or 2² posts under (Make sure all posts you load in the
kiln are directly over these first ones) will allow pots on the bottom to
better get to proper firing temperature. Without the shelf they may fire a
bit cooler.

I have kiln wash (50% alumina hydrate, 25% kaolin, 25% calcined kaolin)
mixed and stored wet in a 2 quart plastic pail with tight fitting lid.
It has sat on the shelf for a couple years - no problems. Be sure to apply
to only one side and don¹t apply to edges.

Bill

Bill Schran
www.creativecreekartisans.com
wsc...@cox.net

On 4/21/16, 9:37 PM, "Clayart on behalf of Ken Chase via Clayart"

<clayart...@lists.clayartworld.com on behalf of
cla...@lists.clayartworld.com> wrote:

[William Schran via Clayart]

Ken,
Have a look at this page:
http://www.clay-king.com/kiln_supplies/kiln_supplies/pyrometric_cones.html
Read all the way down on this page, it will explain how and why cones are
used.

You will note the 1st item is self supporting cones.
I would suggest you start with these.
As the name suggests, you need nothing else to hold the cone vertical at
the correct angle.
They are more expensive than regular large cones but worth it to start.
You want to set the cones in front of the spy hole (gotta plan your
loading of pots with all this in mind) so you will be able to see all 3.
Set them at an angle to your sight, lined at that angle.
If for example you have cones 5, 6, 7, then have cone 5 first, closest to
the spy hole, then 6 and 7 (same with low fire cones).
If you decide you want to view the cones during firing, you should have
them such that there is an element on the wall lined up behind them.
The element is brighter than the kiln atmosphere color so it will back
light the cones.
You also must have proper eye protection.

I use standard large cones and set them in Orton medium standard large
cone plaques with 3 holes.
These are dry ram pressed clay that are intended for one-time use, but I
use them many times.

Feel free to contact me should you have any questions.

Bill

Bill Schran
www.creativecreekartisans.com
wsc...@cox.net

On 4/21/16, 2:00 PM, "Clayart on behalf of Ken Chase via Clayart"

[Sharon Wetherby via Clayart]

Might add note: when using self supporting witness cones, place on
kiln-washed shelves because they could stick to the shelf. I never thought
about this before I test-fired a new kiln w/new shelves w/o kiln wash last
year. Thankfully I placed the witness cones on bisque-fired pieces of
stoneware (w/o kiln wash). The cones stuck.

Sharon Wetherby
Fort Worth, TX

On Fri, Apr 22, 2016 at 9:12 AM, William Schran via Clayart <

URL: <http://lists.clayartworld.com/pipermail/clayart/attachments/20160422/be95e8e6/attachment.html>

[ronroy--- via Clayart]

Most electric kilns fire cooler on the bottom - the trick is not to
cut the heat off from the lower elements. Stack taller pots down
there. Soaking as you get to top temperature will help even out the
temperature as well. It's a good idea to stack tighter in the middle -
plates and platters add extra shelves witch slow down the heat gain.

Davis is right about zone control - you can still sabotage it if you
try hard enough but generally it's a great system. The electronics
sense where it's cooler or hotter and adjust the heat to compensate.

RR

Ron Roy
ron...@ca.inter.net
Web page ronroy.net