Karen and Cliff Sandlin on thu 10 oct 02
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-----Original Message-----
From: Cliff/Karen Sandlin [mailto:sandlink@bellsouth.net]=20
Sent: Thursday, October 10, 2002 10:05 PM
To: 'potterybasics@yahoogroups.com'; 'CLAYART@LSV.CERAMICS.ORG.'
Cc: Subject: kiln opening #3
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I just opened my kiln for the third time in this past week. (To =
refresh: I
have a Skutt 1018 electric kiln with an automatic controller --no
switches-no kiln sitter - no way to operate manually that I know of.=20
1) first firing was at Cone 6, slow speed, with a 30 min. hold (firing
took 14 hrs.). Spectrum (and a few Opulence) glazes cratered, cone 6 =
bent
only very slightly.
2) refire was at Cone 5, slow speed, 30 min. hold (took 13.3 hrs.). =
MANY
more craters on Spectrum pieces. Cone 5's bent only very slightly.)
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Called Skutt. Ordered various self-supporting cones and will test the
firing temps. We offset the cone 6 temp by 10 degrees hotter, but I =
will do
some cone testing before offsetting other temps.
Called Spectrum - they advised that their reactive glazes (the ones I =
like
best that run different colors) are very tricky and will sometimes fire
better at cone 4 (although the label says Cone 4/6)
Called Opulence - they advise their reduction look glazes work best at a =
hot
cone 6 or even cone 7.
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3) my third firing was with a Ramp & Hold schedule that follows the =
Skutt
Manual for a gentle controlled cooling cycle, a 10 min. hold at 2199 and =
a
30 min. hold at 1950. Spectrum also suggested that I might try applying =
a
very thin clear glaze over the dremeled craters before re-firing in an
attempt to save the load.
=20
The clear glaze covered the craters and they are smooth now, although on
some pieces you can see where they were. Still, some of the pieces are =
very
interesting. NONE OF MY CONE 6 CONES BENT MORE THAN SLIGHTLY! I don't =
mean
to be shouting, it is just that I don't understand what this means. Is =
it
possible that the slow speeds or gentle cooling process somehow keeps =
the
cones from bending? According to my cone table, 2199 is a cone 6, =
correct?
Why didn't the cones bend?
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I received emails from two different potters who experienced cratering
problems with Highwater's Desert Buff clay fired at cone 6. It is =
possible
the clay was the problem all along, but my cones still did not bend.
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What I learned: =20
=20
A. Not a good idea to mix glazes even though the label says Cone 4/6. =
I
think I used Spectrum before at Cone 5 with fewer craters. (I probably
won't fire Cone 4 because most of my clays and glazes are 5-6, but maybe
I'll try the highwater clay cone 3-6 and the spectrum glazes and fire at
cone 4.)
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B. I will try less time for the hold - probably 10 min. hold for my 04
bisque and 15-20 min hold for Cone 5.
=20
C. I will check my bisque temperature (cone 04) with witness cones to =
be
sure that is reaching temp.
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D. The more I learn, the more there is to learn and the less I actually
know! It was easier in a classroom atmosphere where we were not allowed =
in
the kiln room and simply accepted all the bad results as possible =
throwing
problems or bad glazes. Never were we allowed to impugn the person =
doing
the firing. =20
=20
I forgot to mention that the clays I used were highwater's Desert Buff =
and
highwater Redstone (as well as Laguna B-Mix cone6 and Laguna #50-which =
did
not crater, but did not have the Spectrum glazes on them either).
Interesting. =20
=20
Thanks everyone for your help!
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=20
=20
Karen
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Chris Schafale on fri 11 oct 02
Hi Karen,
Congratulations on your persistence. This is a frustrating time, I know. When I first
got my kiln and was developing my own glazes, I threw away a LOT of pots with
glaze problems, firing problems, etc. And yes, I was tempted to go back to the
community studio where I could blame someone else or Fate when things didn't
come out right. But ultimately, I find it much more satisfying to work through the
problems myself.
I'm glad that the clear overcoat helped. I'll have to try that one some time. Some
other comments below:
> 2) refire was at Cone 5, slow speed, 30 min. hold (took 13.3 hrs.). MANY
> more craters on Spectrum pieces. Cone 5's bent only very slightly.)
>
This matches my experience with refires, though it's still a mystery why your cones
aren't bending. You really need to use a range of cones, so you can tell what cone
you ARE getting, as well as what cone you are NOT getting.
>
> Called Skutt. Ordered various self-supporting cones and will test the
> firing temps. We offset the cone 6 temp by 10 degrees hotter, but I will do
> some cone testing before offsetting other temps.
Sounds like more offsetting may be in order. Do you mind sharing how this is
done? I don't remember seeing it in my Skutt manual, and I may need to do
something similar on my kiln.
>
> Called Spectrum - they advised that their reactive glazes (the ones I like
> best that run different colors) are very tricky and will sometimes fire
> better at cone 4 (although the label says Cone 4/6)
Aha! Don't you wish they would just tell you that ahead of time???
>
> Called Opulence - they advise their reduction look glazes work best at a hot
> cone 6 or even cone 7.
>
So, not good to mix these two.
>
> Is it
> possible that the slow speeds or gentle cooling process somehow keeps the
> cones from bending? According to my cone table, 2199 is a cone 6, correct?
> Why didn't the cones bend?
The slow speed and gentle cooling will NOT keep the cones from bending. The
whole point of cones is that they measure the "heatwork" -- the combination of heat,
time, and temperature -- experienced by your pots/glazes. You aren't re-using
cones, are you?? If not, I'd say you need to adjust your controller some more, or
replace the thermocouple if it turns out to be way, way off.
>
> > I received emails from two different potters who experienced cratering
> problems with Highwater's Desert Buff clay fired at cone 6. It is possible
> the clay was the problem all along, but my cones still did not bend.
Maybe a combination of factors. I've noticed recently that I'm more apt to get
blisters on Highwater Speckled Brownstone than on the Brownstone without the
speckles, if I overfire. So perhaps these clays interact with the Spectrum glazes in
ways which cause craters AND you have a problem with your controller and/or
thermocouple.
> >
> B. I will try less time for the hold - probably 10 min. hold for my 04
> bisque and 15-20 min hold for Cone 5.
I don't think this is really called for. Holds are generally a Good Thing to help glazes
smooth out.
> >
> C. I will check my bisque temperature (cone 04) with witness cones to be
> sure that is reaching temp.
>
This may or may not make any difference, if the problem is clay-glaze interaction. I
bisque to 06, and that works fine for me.
>
> I forgot to mention that the clays I used were highwater's Desert Buff and
> highwater Redstone (as well as Laguna B-Mix cone6 and Laguna #50-which did
> not crater, but did not have the Spectrum glazes on them either).
> Interesting.
This is a very interesting clue. Might be interesting to put the Spectrum glazes on
the B-mix and see what happens.
Your Highwater clays are rated at cone 4-6 (DB) and cone 3-6 (RS), and looking at
the absorption info Highwater provides, probably are really maturing around cone 5,
possibly getting overfired a little at a true cone 6. I think you'd be fine firing to cone
5 with these clays, if you want to use the Spectrum glazes and find that they don't
crater at cone 5.
Good luck, and get the thermocouple/controller calibrated by firing the kiln empty
with a series of cones, before you waste any more pots.
Chris
>
> Light One Candle Pottery
Fuquay-Varina, North Carolina, USA
(south of Raleigh)
candle@intrex.net
http://www.lightonecandle.com
Dale Cochoy on fri 11 oct 02
----- Original Message -----
From: "Karen and Cliff Sandlin" Subject: FW: kiln opening #3
I responded to this once before. I will again. I had EXACTLY the same
problems, asked the list, and got several answers from people who never had
that but had Ideas what to try...
It sounds like your kiln simply is not firing to what controller says. If
you are firing to 2199 and your cone 6 cones are not bending especially
after a 30 minute hold, well, you aren't firimng that hot!! Exactly like
mine did. In fact, when I decided it was several cones low and removed/sent
controller to manufacturer they said it was about 200 degrees low at cone
6!!. They replaced a chip and all is well. I had it back in about a week. I
also got a good deal on a pyrometer from a NCECCA price given out to me at
the show by Olympic. Now, If I have a concern about temp I can back-up my
tests with a simple reading. My digital controller was FLAWLESS until IT
FAILED, exactly like you describe. Now, It's flawless again. I only use one
cone pack near the thermocouple to double check firing.
Regards,
Dale Cochoy, Wild Things Bonsai Studio, Hartville, Ohio
DaleCochoy@Prodigy.Net http://www.WildThingsBonsai.Com
SNIPS:
2) refire was at Cone 5, slow speed, 30 min. hold (took 13.3 hrs.). MANY
more craters on Spectrum pieces. Cone 5's bent only very slightlyManual for
a gentle controlled cooling cycle, a 10 min. hold at 2199 and a
30 min. hold at 1950The clear glaze covered the craters and they are smooth
now, although on
some pieces you can see where they were. Still, some of the pieces are very
interesting. NONE OF MY CONE 6 CONES BENT MORE THAN SLIGHTLY! I don't mean
to be shouting, it is just that I don't understand what this means. Is it
possible that the slow speeds or gentle cooling process somehow keeps the
cones from bending? According to my cone table, 2199 is a cone 6, correct?
Why didn't the cones bend?
Arnold Howard on fri 11 oct 02
When a controller fires 200 degrees off the programmed temperature,
it is often due to a bad thermocouple. If this happened to me, the
first thing I would do is replace the thermocouple and fire again.
That usually solves the problem. I would replace the controller
only if the temperature were still off.
By the way, before throwing away an old controller, find out if the
factory can have it rebuilt for you. Sometimes that can be done for
a nominal fee.
I told a customer one time that the type-k thermocouples eventually
drift. She was very disappointed to hear that. She had believed
that the digital controller was the most accurate way to fire
ceramics.
The controllers are wonderful. They are fun to use, and reliable.
But they do fail. That's why we recommend using a witness cone with
the controller. That's also why all kiln manufacturers continue to
tell people to monitor the kilns during firing. I don't know of any
who have stopped saying that.
I spoke to a customer who routinely left her digital kiln firing
when she went home at the end of the day. When I suggested that she
wait until the kiln shut off before going home, she said, "If I did
that, I would never keep up with production. There is no way I can
do that." Because the controllers are so reliable, people are
lulled into a false sense of security. They can and do fail.
With best wishes,
Arnold Howard
Paragon Industries, Inc.
--- Dale Cochoy wrote:
> ----- Original Message -----
> From: "Karen and Cliff Sandlin" Subject: FW: kiln opening #3
>
>
>
>
> I responded to this once before. I will again. I had EXACTLY
> the same
> problems, asked the list, and got several answers from people who
> never had
> that but had Ideas what to try...
> It sounds like your kiln simply is not firing to what controller
> says. If
> you are firing to 2199 and your cone 6 cones are not bending
> especially
> after a 30 minute hold, well, you aren't firimng that hot!!
> Exactly like
> mine did. In fact, when I decided it was several cones low and
> removed/sent
> controller to manufacturer they said it was about 200 degrees low
> at cone
> 6!!. They replaced a chip and all is well. I had it back in about
> a week. I
> also got a good deal on a pyrometer from a NCECCA price given out
> to me at
> the show by Olympic. Now, If I have a concern about temp I can
> back-up my
> tests with a simple reading. My digital controller was FLAWLESS
> until IT
> FAILED, exactly like you describe. Now, It's flawless again. I
> only use one
> cone pack near the thermocouple to double check firing.
> Regards,
> Dale Cochoy, Wild Things Bonsai Studio, Hartville, Ohio
> DaleCochoy@Prodigy.Net http://www.WildThingsBonsai.Com
>
> SNIPS:
> 2) refire was at Cone 5, slow speed, 30 min. hold (took 13.3
> hrs.). MANY
> more craters on Spectrum pieces. Cone 5's bent only very
> slightlyManual for
> a gentle controlled cooling cycle, a 10 min. hold at 2199 and a
> 30 min. hold at 1950The clear glaze covered the craters and they
> are smooth
> now, although on
> some pieces you can see where they were. Still, some of the
> pieces are very
> interesting. NONE OF MY CONE 6 CONES BENT MORE THAN SLIGHTLY! I
> don't mean
> to be shouting, it is just that I don't understand what this
> means. Is it
> possible that the slow speeds or gentle cooling process somehow
> keeps the
> cones from bending? According to my cone table, 2199 is a cone
> 6, correct?
> Why didn't the cones bend?
>
>
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