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the strangest cracks ever

updated sat 31 jul 04

 

Jonathan Kirkendall on wed 28 jul 04


Hi all,

In almost 20 years (wow, how did that happen?) of throwing, never seen
this before:

Using Campbell's Cone 6 JB Stoneware. Bisqued a bunch of bowls, slow
bisque, to cone 6. They came out looking fine, no visible cracks.
However, when I glazed them, as the glaze dried, a rather wide crackle
pattern appeared UNDER the glaze - the glaze itself didn't crack, but
rather it looked like I had just glazed a stain glass window. I looked
carefully, nothing on the inside. Tested the bowls gingerly by pulling
to see if the were indeed cracked through and they held up, no problem.

When the bowls came out of the kiln (cone 6 oxidation, firing with John
and Roy's schedule), lo and behold, there were in fact cracks running
across the surface of the outside of the bowl, only say, 1/16 inch
deep. They didn't go through the bowl. The pattern is somewhat
irregular, again, like a stain glass window.

I glazed some more bowls today and found more of this happening - seems
that about 1/2 this order has this cracking.

Has anyone seen this before?

Jonathan in very humid DC

Jennifer Boyer on thu 29 jul 04


Just for the record, I had pots come out of a bisk looking like what
you describe when the bisk was interrupted by a power failure. I
started it again after it had cooled quite a bit and fired it to temp.
The whole kiln load had these faint cracks. They were surface cracks in
a large grid all connecting to each other. They were about an inch(or
more) apart.
They showed up on the top surface of the pots. Nothing went through to
the bottom. Hope you figure this out quick!! Poor Jonathan!
Jennifer, buried in a sea of dinner plates......

On Jul 28, 2004, at 1:20 PM, Jonathan Kirkendall wrote:

> Hi all,
>
> In almost 20 years (wow, how did that happen?) of throwing, never seen
> this before:
>
> Using Campbell's Cone 6 JB Stoneware. Bisqued a bunch of bowls, slow
> bisque, to cone 6. They came out looking fine, no visible cracks.
> However, when I glazed them, as the glaze dried, a rather wide crackle
> pattern appeared UNDER the glaze - the glaze itself didn't crack, but
> rather it looked like I had just glazed a stain glass window. I looked
> carefully, nothing on the inside. Tested the bowls gingerly by pulling
> to see if the were indeed cracked through and they held up, no problem.
>
> When the bowls came out of the kiln (cone 6 oxidation, firing with John
> and Roy's schedule), lo and behold, there were in fact cracks running
> across the surface of the outside of the bowl, only say, 1/16 inch
> deep. They didn't go through the bowl. The pattern is somewhat
> irregular, again, like a stain glass window.
>
> I glazed some more bowls today and found more of this happening - seems
> that about 1/2 this order has this cracking.
>
> Has anyone seen this before?
>
> Jonathan in very humid DC
>
> _______________________________________________________________________
> _______
> 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.
>
>
************************
Jennifer Boyer
Thistle Hill Pottery
Montpelier, VT

http://thistlehillpottery.com

Jonathan Kirkendall on thu 29 jul 04


BINGO!

I forgot that these pots were in the bisque load that only fired part
way because the electric outlet shorted out - once I got everything
fixed I bisqued them again. How odd - I wonder why this happens?

By the way, this has turned out to be the order from hell - just 12
very large salad bowls, blue glaze...what could go wrong? Here's the
list:
1) first batch four or five of the bisqued bowls broke while glazing
2) Threw more. The glaze bubbled.
3) Increased bisque temp, adjusted glaze firing. Glazed batch came out
ok, but just. Not what I'd deliver to a CEO of a large, local
financial institution.
4) Third batch, these bizarre surface cracks.

Honestly, I'm beginning to feel jinxed! I guess I'll make some
offerings today to the studio spirits and throw my fourth set of 12
bowls!

Jonathan in DC
enjoying the relative emptiness of the city during a political
convention. No traffic!

On Thursday, July 29, 2004, at 07:15 AM, Jennifer Boyer wrote:

> Just for the record, I had pots come out of a bisk looking like what
> you describe when the bisk was interrupted by a power failure. I
> started it again after it had cooled quite a bit and fired it to temp.
> The whole kiln load had these faint cracks. They were surface cracks in
> a large grid all connecting to each other. They were about an inch(or
> more) apart.
> They showed up on the top surface of the pots. Nothing went through to
> the bottom. Hope you figure this out quick!! Poor Jonathan!
> Jennifer, buried in a sea of dinner plates......
>
> On Jul 28, 2004, at 1:20 PM, Jonathan Kirkendall wrote:
>
>> Hi all,
>>
>> In almost 20 years (wow, how did that happen?) of throwing, never
>> seen
>> this before:
>>
>> Using Campbell's Cone 6 JB Stoneware. Bisqued a bunch of bowls, slow
>> bisque, to cone 6. They came out looking fine, no visible cracks.
>> However, when I glazed them, as the glaze dried, a rather wide crackle
>> pattern appeared UNDER the glaze - the glaze itself didn't crack, but
>> rather it looked like I had just glazed a stain glass window. I
>> looked
>> carefully, nothing on the inside. Tested the bowls gingerly by
>> pulling
>> to see if the were indeed cracked through and they held up, no
>> problem.
>>
>> When the bowls came out of the kiln (cone 6 oxidation, firing with
>> John
>> and Roy's schedule), lo and behold, there were in fact cracks running
>> across the surface of the outside of the bowl, only say, 1/16 inch
>> deep. They didn't go through the bowl. The pattern is somewhat
>> irregular, again, like a stain glass window.
>>
>> I glazed some more bowls today and found more of this happening -
>> seems
>> that about 1/2 this order has this cracking.
>>
>> Has anyone seen this before?
>>
>> Jonathan in very humid DC
>>
>> ______________________________________________________________________
>> _
>> _______
>> 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.
>>
>>
> ************************
> Jennifer Boyer
> Thistle Hill Pottery
> Montpelier, VT
>
> http://thistlehillpottery.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.
>

Jennifer Boyer on thu 29 jul 04


But Jonathan! You don't recognize your multiple screw ups phase as a
golden opportunity to put your "practice" into practice? observe, don't
judge.....breath deeep

Jennifer, who's blood pressure remains stable when watching a pot hit
the ground...;-)

PS I'm in the middle of throwing replacements for 12 small and large
plates that a customer thinks are too shallow.....breating, breathing
On Jul 29, 2004, at 8:40 AM, Jonathan Kirkendall wrote:

> BINGO!
>
> I forgot that these pots were in the bisque load that only fired part
> way because the electric outlet shorted out - once I got everything
> fixed I bisqued them again. How odd - I wonder why this happens?
>
> By the way, this has turned out to be the order from hell - just 12
> very large salad bowls, blue glaze...what could go wrong? Here's the
> list:
> 1) first batch four or five of the bisqued bowls broke while glazing
> 2) Threw more. The glaze bubbled.
> 3) Increased bisque temp, adjusted glaze firing. Glazed batch came out
> ok, but just. Not what I'd deliver to a CEO of a large, local
> financial institution.
> 4) Third batch, these bizarre surface cracks.
>
> Honestly, I'm beginning to feel jinxed! I guess I'll make some
> offerings today to the studio spirits and throw my fourth set of 12
> bowls!
>
> Jonathan in DC
> enjoying the relative emptiness of the city during a political
> convention. No traffic!
>
> On Thursday, July 29, 2004, at 07:15 AM, Jennifer Boyer wrote:
>
>> Just for the record, I had pots come out of a bisk looking like what
>> you describe when the bisk was interrupted by a power failure. I
>> started it again after it had cooled quite a bit and fired it to temp.
>> The whole kiln load had these faint cracks. They were surface cracks
>> in
>> a large grid all connecting to each other. They were about an inch(or
>> more) apart.
>> They showed up on the top surface of the pots. Nothing went through to
>> the bottom. Hope you figure this out quick!! Poor Jonathan!
>> Jennifer, buried in a sea of dinner plates......
>>
>> On Jul 28, 2004, at 1:20 PM, Jonathan Kirkendall wrote:
>>
>>> Hi all,
>>>
>>> In almost 20 years (wow, how did that happen?) of throwing, never
>>> seen
>>> this before:
>>>
>>> Using Campbell's Cone 6 JB Stoneware. Bisqued a bunch of bowls, slow
>>> bisque, to cone 6. They came out looking fine, no visible cracks.
>>> However, when I glazed them, as the glaze dried, a rather wide
>>> crackle
>>> pattern appeared UNDER the glaze - the glaze itself didn't crack, but
>>> rather it looked like I had just glazed a stain glass window. I
>>> looked
>>> carefully, nothing on the inside. Tested the bowls gingerly by
>>> pulling
>>> to see if the were indeed cracked through and they held up, no
>>> problem.
>>>
>>> When the bowls came out of the kiln (cone 6 oxidation, firing with
>>> John
>>> and Roy's schedule), lo and behold, there were in fact cracks running
>>> across the surface of the outside of the bowl, only say, 1/16 inch
>>> deep. They didn't go through the bowl. The pattern is somewhat
>>> irregular, again, like a stain glass window.
>>>
>>> I glazed some more bowls today and found more of this happening -
>>> seems
>>> that about 1/2 this order has this cracking.
>>>
>>> Has anyone seen this before?
>>>
>>> Jonathan in very humid DC
>>>
>>> _____________________________________________________________________
>>> _
>>> _
>>> _______
>>> 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.
>>>
>>>
>> ************************
>> Jennifer Boyer
>> Thistle Hill Pottery
>> Montpelier, VT
>>
>> http://thistlehillpottery.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.
>
>
************************
Jennifer Boyer
Thistle Hill Pottery
Montpelier, VT

http://thistlehillpottery.com

Mike Martino on thu 29 jul 04


Hi Jonathan,

I get these on my tea ceremony waterjars when they dry unevenly. Mostly the
bottom third of the pot. Invisible to the eye, but show up when the glaze is
applied. If fired, they usually go through the wall, but since I use a very
heavy glaze on the inside of the pot, it plugs the holes for me. If I'm
lucky, it even comes through the wall to the outside a bit. Looks cool.
However, if the piece is larger you run the risk of a full blown collapse
onto your other stuff during firing.

If you want to see if you have the cracking before you glaze brush the
surface with kerosene or similar. You'll see the cracks if they are there,
and the stuff will evaporate quickly so you can continue glazing.


Mike

in Taku, Japan


-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of Jonathan
Kirkendall
Sent: Thursday, July 29, 2004 2:20 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: The Strangest Cracks Ever


Hi all,

In almost 20 years (wow, how did that happen?) of throwing, never seen
this before:

Using Campbell's Cone 6 JB Stoneware. Bisqued a bunch of bowls, slow
bisque, to cone 6. They came out looking fine, no visible cracks.
However, when I glazed them, as the glaze dried, a rather wide crackle
pattern appeared UNDER the glaze - the glaze itself didn't crack, but
rather it looked like I had just glazed a stain glass window. I looked
carefully, nothing on the inside. Tested the bowls gingerly by pulling
to see if the were indeed cracked through and they held up, no problem.

When the bowls came out of the kiln (cone 6 oxidation, firing with John
and Roy's schedule), lo and behold, there were in fact cracks running
across the surface of the outside of the bowl, only say, 1/16 inch
deep. They didn't go through the bowl. The pattern is somewhat
irregular, again, like a stain glass window.

I glazed some more bowls today and found more of this happening - seems
that about 1/2 this order has this cracking.

Has anyone seen this before?

Jonathan in very humid DC

____________________________________________________________________________
__
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.

Kathi LeSueur on thu 29 jul 04


jon@KIRKENDALLPOTTERY.COM wrote:

> BINGO!
>
> I forgot that these pots were in the bisque load that only fired part
> way because the electric outlet shorted out - once I got everything
> fixed I bisqued them again. How odd - I wonder why this happens?>>>


Many years ago I had a kiln I used for bisque hooked up to inadequate
wiring. The circuit breaker would trip. I'd wait a few minutes and then
reset it and turn on the kiln. What I found after many lost pots is that
if the breaker tripped at the wrong point the pots would crack just like
you describe. I had many arguments with my then partner about having an
electrician upgrade the service. But it was a rental and she didn't want
to go to the expense. It would have been cheaper in the long run if we had.

Interruptions of firings can have little or no consequences or be a
disaster depending on the temperature the interruption occurred at.

Kathi

>
>
>

Darnie Sizemore on thu 29 jul 04


Your strange cracks in a uncompleted bisque, may be because the kiln got to quartz conversion but never finished. So the clay started to become ceramic, and never finished, the clay never was permanently bonded. This is just a theory, not articulated well.

Darnie

Jonathan Kirkendall wrote:
BINGO!

I forgot that these pots were in the bisque load that only fired part
way because the electric outlet shorted out - once I got everything
fixed I bisqued them again. How odd - I wonder why this happens?

By the way, this has turned out to be the order from hell - just 12
very large salad bowls, blue glaze...what could go wrong? Here's the
list:
1) first batch four or five of the bisqued bowls broke while glazing
2) Threw more. The glaze bubbled.
3) Increased bisque temp, adjusted glaze firing. Glazed batch came out
ok, but just. Not what I'd deliver to a CEO of a large, local
financial institution.
4) Third batch, these bizarre surface cracks.

Honestly, I'm beginning to feel jinxed! I guess I'll make some
offerings today to the studio spirits and throw my fourth set of 12
bowls!

Jonathan in DC
enjoying the relative emptiness of the city during a political
convention. No traffic!

On Thursday, July 29, 2004, at 07:15 AM, Jennifer Boyer wrote:

> Just for the record, I had pots come out of a bisk looking like what
> you describe when the bisk was interrupted by a power failure. I
> started it again after it had cooled quite a bit and fired it to temp.
> The whole kiln load had these faint cracks. They were surface cracks in
> a large grid all connecting to each other. They were about an inch(or
> more) apart.
> They showed up on the top surface of the pots. Nothing went through to
> the bottom. Hope you figure this out quick!! Poor Jonathan!
> Jennifer, buried in a sea of dinner plates......
>
> On Jul 28, 2004, at 1:20 PM, Jonathan Kirkendall wrote:
>
>> Hi all,
>>
>> In almost 20 years (wow, how did that happen?) of throwing, never
>> seen
>> this before:
>>
>> Using Campbell's Cone 6 JB Stoneware. Bisqued a bunch of bowls, slow
>> bisque, to cone 6. They came out looking fine, no visible cracks.
>> However, when I glazed them, as the glaze dried, a rather wide crackle
>> pattern appeared UNDER the glaze - the glaze itself didn't crack, but
>> rather it looked like I had just glazed a stain glass window. I
>> looked
>> carefully, nothing on the inside. Tested the bowls gingerly by
>> pulling
>> to see if the were indeed cracked through and they held up, no
>> problem.
>>
>> When the bowls came out of the kiln (cone 6 oxidation, firing with
>> John
>> and Roy's schedule), lo and behold, there were in fact cracks running
>> across the surface of the outside of the bowl, only say, 1/16 inch
>> deep. They didn't go through the bowl. The pattern is somewhat
>> irregular, again, like a stain glass window.
>>
>> I glazed some more bowls today and found more of this happening -
>> seems
>> that about 1/2 this order has this cracking.
>>
>> Has anyone seen this before?
>>
>> Jonathan in very humid DC
>>
>> ______________________________________________________________________
>> _
>> _______
>> 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.
>>
>>
> ************************
> Jennifer Boyer
> Thistle Hill Pottery
> Montpelier, VT
>
> http://thistlehillpottery.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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Ron Roy on mon 2 aug 04


Hi Jonathan,

Tell us more - you wedging? What kind of wedging?

Sounds like the clay may be delaminated and the outsde clay is shrinking
more than the inside clay- is it possible to pry off part of the outside
layer - from a bisqued pot?

Is this the only clay you use from Campbells?

Never seen this in all my years of dealing with clay.

RR


>Using Campbell's Cone 6 JB Stoneware. Bisqued a bunch of bowls, slow
>bisque, to cone 6. They came out looking fine, no visible cracks.
>However, when I glazed them, as the glaze dried, a rather wide crackle
>pattern appeared UNDER the glaze - the glaze itself didn't crack, but
>rather it looked like I had just glazed a stain glass window. I looked
>carefully, nothing on the inside. Tested the bowls gingerly by pulling
>to see if the were indeed cracked through and they held up, no problem.
>
>When the bowls came out of the kiln (cone 6 oxidation, firing with John
>and Roy's schedule), lo and behold, there were in fact cracks running
>across the surface of the outside of the bowl, only say, 1/16 inch
>deep. They didn't go through the bowl. The pattern is somewhat
>irregular, again, like a stain glass window.
>
>I glazed some more bowls today and found more of this happening - seems
>that about 1/2 this order has this cracking.

Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513