sumiko braithwaite on sat 22 jul 06
Hello to All
I have recently become a member and i really enjoy
reading all the mail. I have learned a lot. Maybe
someone can help me with a problem I have been having.
I make "doublewall" pottery and I have a lot of
success with it but I do have one problem that I just
can't figure out. When I make the outer wall, I put a
1/2 inch diameter hole in the bottom. There are
several reasons for this. Suffice it to say, I need
the hole there.
Here is my problem. The first time I high fire
everything is usually ok. If I have to re-fire for
any reason, reglaze, gold trim etc I sometimes get a
crack across the bottom hole.
I use Laguna B mix. I also fire with slow cooling.
It takes over 16 hours firing time from start to
finish. It doesn't happen all the time but often
enough to break my heart.
Any ideas would be appreciated. Do you think I need
to change the clay I use? I like working with b-mix.
Sumiko Braithwaite from sunny San Diego.
www.ceramicsbysumiko.com
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sumiko braithwaite on sun 23 jul 06
To Ron and Elizabeth,
Thanks again for your comments. I wasn't aware I
couldn't post pictures here. If you would like to see
what I was talking about check it out at:
www.sumiko.s5.com
Thanks Elizabeth for your kind words about my work.
Sumiko in sunny San Diego
www.ceramicsbysumiko.com
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Ron Roy on sun 23 jul 06
Hi Sumiko,
It may be happening on the way up during the 2nd firing. Break one in half
and look to see if any glaze has melted around the crack - in other words -
not sharp at the cracked edge. If that is the case and it has cracked on
the way up you will have to fire up slower - probably during the quartz
inversion - say 500 to 600 degrees.
You may also find - if you can - re-enforce the edge of the hole - leaving
it thicker will probably cure the problem.
RR
>Hello to All
>I have recently become a member and i really enjoy
>reading all the mail. I have learned a lot. Maybe
>someone can help me with a problem I have been having.
>I make "doublewall" pottery and I have a lot of
>success with it but I do have one problem that I just
>can't figure out. When I make the outer wall, I put a
>1/2 inch diameter hole in the bottom. There are
>several reasons for this. Suffice it to say, I need
>the hole there.
>Here is my problem. The first time I high fire
>everything is usually ok. If I have to re-fire for
>any reason, reglaze, gold trim etc I sometimes get a
>crack across the bottom hole.
>I use Laguna B mix. I also fire with slow cooling.
>It takes over 16 hours firing time from start to
>finish. It doesn't happen all the time but often
>enough to break my heart.
>Any ideas would be appreciated. Do you think I need
>to change the clay I use? I like working with b-mix.
>Sumiko Braithwaite from sunny San Diego.
>www.ceramicsbysumiko.com
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
sumiko braithwaite on sun 23 jul 06
Hi Ron,
Thank you for your suggestion. I will try firing up
slower. I didn't mention it in the last post but I am
using a Skutt Automatic kiln. Here is the firing
schedule I normally use.
Seg't Rate Temp Hold
1 200 185 2 Hrs
2 360 1032 0
3 180 1132 0
4 200 2050 0
5 108 2199 30 Min
6 5000 1960 0
7 150 1100 0
Then I let it cool to 85 or 90 degrees before opening.
I will try slower rate speeds for segments 1 and 2.
I am attaching a photo of the last one I had a problem
with. This is not nearly as bad as some I get. The
really bad ones have already been destroyed. Do you
think the bottom is thick enough? This one is
approximately ¼ inch. Thank you very much.
Sumiko in sunny San Diego
www.ceramicsbysumiko.com
--- Ron Roy wrote:
> Hi Sumiko,
>
> It may be happening on the way up during the 2nd
> firing. Break one in half
> and look to see if any glaze has melted around the
> crack - in other words -
> not sharp at the cracked edge. If that is the case
> and it has cracked on
> the way up you will have to fire up slower -
> probably during the quartz
> inversion - say 500 to 600 degrees.
>
> You may also find - if you can - re-enforce the edge
> of the hole - leaving
> it thicker will probably cure the problem.
>
> RR
>
>
> >Hello to All
> >I have recently become a member and i really enjoy
> >reading all the mail. I have learned a lot. Maybe
> >someone can help me with a problem I have been
> having.
> >I make "doublewall" pottery and I have a lot of
> >success with it but I do have one problem that I
> just
> >can't figure out. When I make the outer wall, I
> put a
> >1/2 inch diameter hole in the bottom. There are
> >several reasons for this. Suffice it to say, I
> need
> >the hole there.
> >Here is my problem. The first time I high fire
> >everything is usually ok. If I have to re-fire for
> >any reason, reglaze, gold trim etc I sometimes get
> a
> >crack across the bottom hole.
> >I use Laguna B mix. I also fire with slow cooling.
> >It takes over 16 hours firing time from start to
> >finish. It doesn't happen all the time but often
> >enough to break my heart.
> >Any ideas would be appreciated. Do you think I
> need
> >to change the clay I use? I like working with
> b-mix.
> >Sumiko Braithwaite from sunny San Diego.
> >www.ceramicsbysumiko.com
>
> Ron Roy
> RR#4
> 15084 Little Lake Road
> Brighton, Ontario
> Canada
> K0K 1H0
>
>
______________________________________________________________________________
> 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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Elizabeth Priddy on sun 23 jul 06
I would offer this suggestion.
I cannot see the picture you mentioned, because photos
don't come with clayart mail, but I looked on your
site to see what type of work you are making.
It is really beautiful and I see why losing one is
painful.
If you make the exterior wall of the pot as normal and
close it in...if you look on the inside of it, it will
probably look like an inverted dimple at the center
point. This means that the wall is tapering to a
point, due to the nature of the construction. Even if
you cut a small hole at the center of the "foot" of
the pot after trimming, you still would have an uneven
foot that is tapering to thinness at the center. And
unevenness of moisture or thickness is what causes
cracks in my experience.
So what I suggest is this, when you close in the form,
while it is upside down, add a ball of clay to the top
which will become the foot. Center the small ball of
clay on the top and leave it slightly domed. Then
flatten it off with a rib and turn your foot out of
it. This additional ball should stick with no problem
and add enough even thickness to the floor of the
exterior wall of the finished form to make it sturdier
on frequent firings. The flattening will hopefully
revert that dimple to flat on the interior, or at
least add enough thickness to the foot that the slight
taper is compensated for. The added weight to the
piece should also prevent tippiness, as I would guess
that those forms might be a little topheavvy when
complete and with flowers.
I hope this made sense. If I am mistaken about how
you are making these, please disregard.
Your work is really beautiful. Thanks for including
your website. I enjoy seeing new folks on clayart
that are obviously not new folks to clay.
Good luck with everything.
Elizabeth
Elizabeth Priddy
Beaufort, NC - USA
http://www.elizabethpriddy.com
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William & Susan Schran User on mon 24 jul 06
On 7/24/06 1:24 AM, "sumiko braithwaite" wrote:
> If you would like to see
> what I was talking about check it out at:
> www.sumiko.s5.com
> Thanks Elizabeth for your kind words about my work.
> Sumiko in sunny San Diego
> www.ceramicsbysumiko.com
Sumiko,
I looked at the example of the cracking and at your web site, noting these
are double walled forms.
I would imagine the thickness of the bottom at the junction of the outer
wall is sufficiently thick enough relative to the area of the opening that
is setting up an opportunity for cracking due to stress. Fine particle
clays, such as porcelain & B-Mix will be more prone to this issue.
If changing clays is not an option, I would suggest two things.
#1 - Enlarge the hole in the bottom, almost out to the foot. This may lead
to some warping, so a layer of extremely fine grog or powdered alumina on
the shelf for glaze firing might be necessary.
#2 - As was mentioned in another post - throw the form upside down. Open the
clay to the wheel head, split the donut, pull up the inner wall enclosing at
top to form the inner container, then pull up the outer wall a bit higher
than the inner form.
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
sumiko braithwaite on mon 24 jul 06
Hello Bill,
Thank you for the suggestion re the size of the hole.
I hadn't thought of that. I will try it next time. I
would prefer not changing the clay. I like the way
bmix works.
Sumiko in sunny san diego
www.ceramicsbysumiko.com
--- William & Susan Schran User
wrote:
> On 7/24/06 1:24 AM, "sumiko braithwaite"
> wrote:
>
> > If you would like to see
> > what I was talking about check it out at:
> > www.sumiko.s5.com
> > Thanks Elizabeth for your kind words about my
> work.
> > Sumiko in sunny San Diego
> > www.ceramicsbysumiko.com
>
> Sumiko,
>
> I looked at the example of the cracking and at your
> web site, noting these
> are double walled forms.
>
> I would imagine the thickness of the bottom at the
> junction of the outer
> wall is sufficiently thick enough relative to the
> area of the opening that
> is setting up an opportunity for cracking due to
> stress. Fine particle
> clays, such as porcelain & B-Mix will be more prone
> to this issue.
>
> If changing clays is not an option, I would suggest
> two things.
>
> #1 - Enlarge the hole in the bottom, almost out to
> the foot. This may lead
> to some warping, so a layer of extremely fine grog
> or powdered alumina on
> the shelf for glaze firing might be necessary.
>
> #2 - As was mentioned in another post - throw the
> form upside down. Open the
> clay to the wheel head, split the donut, pull up the
> inner wall enclosing at
> top to form the inner container, then pull up the
> outer wall a bit higher
> than the inner form.
>
>
> -- William "Bill" Schran
> Fredericksburg, Virginia
> wschran@cox.net
> wschran@nvcc.edu
>
>
______________________________________________________________________________
> 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 24 jul 06
Are the edags of the glaze - where cracked - sharp or rounded?
You di not send a picture bit kkep it unse 100K please.
RR
>Hi Ron,
>Thank you for your suggestion. I will try firing up
>slower. I didn't mention it in the last post but I am
>using a Skutt Automatic kiln. Here is the firing
>schedule I normally use.
>Seg't Rate Temp Hold
>1 200 185 2 Hrs
>2 360 1032 0
>3 180 1132 0
>4 200 2050 0
>5 108 2199 30 Min
>6 5000 1960 0
>7 150 1100 0
>Then I let it cool to 85 or 90 degrees before opening.
>I will try slower rate speeds for segments 1 and 2.
>I am attaching a photo of the last one I had a problem
>with. This is not nearly as bad as some I get. The
>really bad ones have already been destroyed. Do you
>think the bottom is thick enough? This one is
>approximately =BC inch. Thank you very much.
>Sumiko in sunny San Diego
>www.ceramicsbysumiko.com
>
>
>
>--- Ron Roy wrote:
>
>> Hi Sumiko,
>>
>> It may be happening on the way up during the 2nd
>> firing. Break one in half
>> and look to see if any glaze has melted around the
>> crack - in other words -
>> not sharp at the cracked edge. If that is the case
>> and it has cracked on
>> the way up you will have to fire up slower -
>> probably during the quartz
>> inversion - say 500 to 600 degrees.
>>
>> You may also find - if you can - re-enforce the edge
>> of the hole - leaving
>> it thicker will probably cure the problem.
>>
>> RR
>>
>>
>> >Hello to All
>> >I have recently become a member and i really enjoy
>> >reading all the mail. I have learned a lot. Maybe
>> >someone can help me with a problem I have been
>> having.
>> >I make "doublewall" pottery and I have a lot of
>> >success with it but I do have one problem that I
>> just
>> >can't figure out. When I make the outer wall, I
>> put a
>> >1/2 inch diameter hole in the bottom. There are
>> >several reasons for this. Suffice it to say, I
>> need
>> >the hole there.
>> >Here is my problem. The first time I high fire
>> >everything is usually ok. If I have to re-fire for
>> >any reason, reglaze, gold trim etc I sometimes get
>> a
>> >crack across the bottom hole.
>> >I use Laguna B mix. I also fire with slow cooling.
>> >It takes over 16 hours firing time from start to
>> >finish. It doesn't happen all the time but often
>> >enough to break my heart.
>> >Any ideas would be appreciated. Do you think I
>> need
>> >to change the clay I use? I like working with
>> b-mix.
>> >Sumiko Braithwaite from sunny San Diego.
>> >www.ceramicsbysumiko.com
>>
>> Ron Roy
>> RR#4
>> 15084 Little Lake Road
>> Brighton, Ontario
>> Canada
>> K0K 1H0
>>
>>
>___________________________________________________________________________=
___
>> 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!?
>Tired of spam? Yahoo! Mail has the best spam protection around
>http://mail.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.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Ron Roy on fri 28 jul 06
Hi Sumiko,
Get a copy of "The Potters Dictionary of Materials and Techniques' by Frank
and Janet Hamer - under cracks - you will find many pages of pictures of
cracks - find the kind of cracks you have and it will expalin how it
happened.
RR
>To Ron and Elizabeth,
>Thanks again for your comments. I wasn't aware I
>couldn't post pictures here. If you would like to see
>what I was talking about check it out at:
>www.sumiko.s5.com
>Thanks Elizabeth for your kind words about my work.
>Sumiko in sunny San Diego
>www.ceramicsbysumiko.com
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
sumiko braithwaite on sun 30 jul 06
Ron,
Thanks again for the info. I found the book you
recommended in the San Diego Library system. I had to
have them send it to my local branch. I havn't seen
it yet but it should be here in a couple of days. I
will probably wind up buying one. Thanks again. I
really appreciate all the helpful responses I have
been getting.
Sumiko in Sunny (AND HOT!!!) San Diego
www.ceramicsbysumiko.com
Ron Roy wrote:
> Hi Sumiko,
>
> Get a copy of "The Potters Dictionary of Materials
> and Techniques' by Frank
> and Janet Hamer - under cracks - you will find many
> pages of pictures of
> cracks - find the kind of cracks you have and it
> will expalin how it
> happened.
>
> RR
>
> >To Ron and Elizabeth,
> >Thanks again for your comments. I wasn't aware I
> >couldn't post pictures here. If you would like to
> see
> >what I was talking about check it out at:
> >www.sumiko.s5.com
> >Thanks Elizabeth for your kind words about my work.
> >Sumiko in sunny San Diego
> >www.ceramicsbysumiko.com
>
> Ron Roy
> RR#4
> 15084 Little Lake Road
> Brighton, Ontario
> Canada
> K0K 1H0
>
>
______________________________________________________________________________
> 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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