Bob Johnson on mon 30 nov 09
I've been having increasing problems with pinholes, and I think it has
something to do with my clay. In my last firing (^6 reduction), half of the
pots were unusable because of this defect.
But there's more to the puzzle: All the pinholed pots were made from clay
that had been around my studio for several months (stoneware, some of which
had been through my pug mill a time or two). The pots that didn't pinhole
were made from new boxes of ^10 half-porcelain/half-white-stoneware clay.
The same glazes were used on both clays. Is it possible that aging clay
undergoes a chemical reaction that produces more and more pinholes? Or is m=
y
old clay getting contaminated, somehow?
Possible clues: (1) We have hard water that we run through a water softener
to remove dissolved lime and iron-although both batches of pots were thrown
using this softened water. (2) My pug mill has developed some scabrous
deposits that seem to be the clay and water reacting to the aluminum
housing-although I have not seen any mysterious chunks in the clay.
Any ideas?
Bob
----------------------
Robert Johnson
Roseburg, Oregon
http://www.flickr.com/photos/psychoceramics/
David McBeth on tue 1 dec 09
I am lookig for answers to the same question. I am tryng a higher.
slower bisque firing to see if the culprit is unfired organics.
Dave
On 12/1/09, Bob Johnson wrote:
> I've been having increasing problems with pinholes, and I think it has
> something to do with my clay. In my last firing (^6 reduction), half of =
the
> pots were unusable because of this defect.
>
>
>
> But there's more to the puzzle: All the pinholed pots were made from cla=
y
> that had been around my studio for several months (stoneware, some of wh=
ich
> had been through my pug mill a time or two). The pots that didn't pinhol=
e
> were made from new boxes of ^10 half-porcelain/half-white-stoneware clay=
.
> The same glazes were used on both clays. Is it possible that aging clay
> undergoes a chemical reaction that produces more and more pinholes? Or i=
s my
> old clay getting contaminated, somehow?
>
>
>
> Possible clues: (1) We have hard water that we run through a water softe=
ner
> to remove dissolved lime and iron-although both batches of pots were thr=
own
> using this softened water. (2) My pug mill has developed some scabrous
> deposits that seem to be the clay and water reacting to the aluminum
> housing-although I have not seen any mysterious chunks in the clay.
>
>
>
> Any ideas?
>
>
>
> Bob
>
>
>
> ----------------------
>
> Robert Johnson
> Roseburg, Oregon
> http://www.flickr.com/photos/psychoceramics/
>
--
David McBeth
Professor of Art
Department of Visual and Theatre Arts
University of Tennessee - Martin
731-881-7416
Lee Love on tue 1 dec 09
Do you see pinholes right after glazing? Lowtemp bisque will cause
these. You can get rid of them by sponging before glazing.
--
Lee, a Mashiko potter in Minneapolis
http://mashikopots.blogspot.com/
"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D97tha=
t is, "T=3D
he
land of eternal youth is behind the house, a beautiful land fluent
within itself." -- John O'Donohue
Ron Roy on thu 3 dec 09
Hi Bob,
Could be the extra mixing is responsible - you need to test the boxed clay
for absorbency - see how much there is - could be a tight body that did not
need much more mixing to over fire. Do you think it was all from the same
batch?
It's the only thing I can think of.
RR
On Tue, Dec 1, 2009 at 1:46 AM, Bob Johnson wrote:
> I've been having increasing problems with pinholes, and I think it has
> something to do with my clay. In my last firing (^6 reduction), half of t=
he
> pots were unusable because of this defect.
>
>
>
> But there's more to the puzzle: All the pinholed pots were made from clay
> that had been around my studio for several months (stoneware, some of whi=
ch
> had been through my pug mill a time or two). The pots that didn't pinhole
> were made from new boxes of ^10 half-porcelain/half-white-stoneware clay.
> The same glazes were used on both clays. Is it possible that aging clay
> undergoes a chemical reaction that produces more and more pinholes? Or is
> my
> old clay getting contaminated, somehow?
>
>
>
> Possible clues: (1) We have hard water that we run through a water soften=
er
> to remove dissolved lime and iron-although both batches of pots were thro=
wn
> using this softened water. (2) My pug mill has developed some scabrous
> deposits that seem to be the clay and water reacting to the aluminum
> housing-although I have not seen any mysterious chunks in the clay.
>
>
>
> Any ideas?
>
>
>
> Bob
>
>
>
> ----------------------
>
> Robert Johnson
> Roseburg, Oregon
> http://www.flickr.com/photos/psychoceramics/
>
--
Ron Roy
15084 Little Lake Road
Brighton, Ontario, Canada
K0K 1H0
| |
|
