Dave Finkelnburg on sun 28 may 06
Randy,
Pinholing is a very complex phenomenon. Vapor in
pore spaces in the bisque and the glaze itself can
contribute. Thermal decomposition of oxides can also
put vapor into the glaze. Thermal dehydroxylation of
frits can have a similar effect, if a frit is in the
glaze. So, it is not necessarily a dirty bisque that
is at fault. In your situation it sounds as if it is
some of your glazes, or their ingredients, not the
bisque, that is the cause.
I assume you have already got some thoughts about
what it is about certain of your glazes that is
causing this.
Good potting,
Dave Finkelnburg
--- Randy McCall wrote:
If all the cones were even on each shelf in
> the firing and some glazes pinholed and some did not
> pinhole would bisque be a problem or could that be
eliminated?
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Randy McCall on sun 28 may 06
I have a question on pinholing? If all the cones were even on each shelf in
the firing and some glazes pinholed and some did not pinhole would bisque be
a problem or could that be eliminated?
Randy
South Carolina
Pottery Web site
http://members.tripod.com/~McCallJ/index.html
Lynn Goodman Porcelain Pottery on mon 29 may 06
What do you bisque at? Take it up a cone and do a really slow firing.
That will allow more of the gases that are causing the pinholing to
escape before they ruin your work.
Lynn
On May 28, 2006, at 8:57 PM, Randy McCall wrote:
> I have a question on pinholing? If all the cones were even on each
> shelf in
> the firing and some glazes pinholed and some did not pinhole would
> bisque be
> a problem or could that be eliminated?
>
>
> Randy
> South Carolina
> Pottery Web site
>
> http://members.tripod.com/~McCallJ/index.html
>
> _______________________________________________________________________
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> Send postings to clayart@lsv.ceramics.org
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>
>
Lynn Goodman
Fine Porcelain Pottery
548 Court St.
Brooklyn, NY 11231
718-858-6920
Cell 347-526-9805
www.lynngoodmanporcelain.com
Ivor and Olive Lewis on tue 30 may 06
Dear Dave Finkelnburg,=20
Dehydroxylation of a raw clay I can understand. But do Frits undergo =
this chemical reaction ? I was under the impression that they were =
pretty well ground glass. Can you please explain and give some examples.
Certainly some oxides decompose, Fe2O3 being a good example. And what =
about the fate of Carbon dioxide from the decomposition of the Alkali =
Earth elements carbonates?
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Ron Roy on tue 30 may 06
Hi Randy -
If you refire and it does not help or makes it worse - then it's probably
the bisque.
If only some pots are pin holing - it can still be the bisque because some
bisque firings are uneven. The organics could be burned off in a hotter
part of the kiln but not in a cooler part - you would then probably have
pin holed scattered throughout your glaze firing.
Maybe it's because the glaze firing is uneven - you would know because the
pin holed pots would be together - best to check evenness with cones on all
levels once in a while. Cones can save you a lot of trouble - probably the
least expensive diagnostic help we have.
Some think that there is no problem with fast firing bisque but under the
right (wrong) circumstances it can make a big difference. Some would never
soak a bisque firing but it is a good way to help even a kiln out no mater
what kind of firing.
RR
>I have a question on pinholing? If all the cones were even on each shelf in
>the firing and some glazes pinholed and some did not pinhole would bisque be
>a problem or could that be eliminated?
>
>
>Randy
>South Carolina
>Pottery Web site
>
>http://members.tripod.com/~McCallJ/index.html
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
cliff daniels on tue 30 may 06
Randy, I'd be interested if it is just the larger
pieces. I have this problem. I am glaze firing
today using a slower firing schedule with the
idea that the larger and thicker pieces lag
behind a little. I tried a longer soak last time
45 minutes at 2150, but I got warping. I have
tried 5 different clay bodies--no difference. I
am hoping a slower schedule won't affect color
brilliance, and will keep a slow cool down for
crystal formation.
Ron? will this affect color? My automatic slow
fire program gives pretty boring results, but
that does not include slow cooling.
--- Ron Roy wrote:
> Hi Randy -
>
> If you refire and it does not help or makes it
> worse - then it's probably
> the bisque.
>
> If only some pots are pin holing - it can still
> be the bisque because some
> bisque firings are uneven. The organics could
> be burned off in a hotter
> part of the kiln but not in a cooler part - you
> would then probably have
> pin holed scattered throughout your glaze
> firing.
>
> Maybe it's because the glaze firing is uneven -
> you would know because the
> pin holed pots would be together - best to
> check evenness with cones on all
> levels once in a while. Cones can save you a
> lot of trouble - probably the
> least expensive diagnostic help we have.
>
> Some think that there is no problem with fast
> firing bisque but under the
> right (wrong) circumstances it can make a big
> difference. Some would never
> soak a bisque firing but it is a good way to
> help even a kiln out no mater
> what kind of firing.
>
> RR
>
>
>
> >I have a question on pinholing? If all the
> cones were even on each shelf in
> >the firing and some glazes pinholed and some
> did not pinhole would bisque be
> >a problem or could that be eliminated?
> >
> >
> >Randy
> >South Carolina
> >Pottery Web site
> >
> >http://members.tripod.com/~McCallJ/index.html
>
> 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.
>
The Mud Man
Clifford Daniels
1 Calvin Coombs Rd.
Colrain, MA 01340
413-624-0251
mudmanpottery@yahoo.com
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Ron Roy on wed 31 may 06
HI Cliff,
I would expect some changes - trick is to just do enough to get rid of the
pin holes and change everything else as little as possible. Sounds like in
your case the glaze needs a little change - try dropping the clay a percent
or two to loosen the glaze a little. Do a few small tests to find out.
RR
>Randy, I'd be interested if it is just the larger
>pieces. I have this problem. I am glaze firing
>today using a slower firing schedule with the
>idea that the larger and thicker pieces lag
>behind a little. I tried a longer soak last time
>45 minutes at 2150, but I got warping. I have
>tried 5 different clay bodies--no difference. I
>am hoping a slower schedule won't affect color
>brilliance, and will keep a slow cool down for
>crystal formation.
>
>Ron? will this affect color? My automatic slow
>fire program gives pretty boring results, but
>that does not include slow cooling.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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