claybair on tue 20 jun 06
Yikes...
I haven't followed this thread until I just saw
the glaze in question.
Three years ago I took issue with Duncan
Diamond Clear which is very popular in the
paint your own shops. When I questioned them
about the lead content I was told it was 26%.
It turned an over the counter lead test kit stick bright pink.
See
http://www.potters.org/subject71137.htm
for details and response from Monona Rossol.
There are several issues here... yes they meet gov't
guidelines BUT the guidelines were issued in 1970.
Those guidelines were limited by the equipment used for testing.
This brings me back to the over the counter lead test kit which is
much more sensitive than state of the art 1970 equipment.
The guidelines are antiquated.
I sure hope the once fired porcelain is not functional ware.
Please tell me it's sculpture or some such.
Gayle Bair
Bainbridge Island, WA
Tucson, AZ
http://claybair.com
-----Original Message-----
From: Snail Scott
At 01:47 AM 6/20/2006 -0500, you wrote:
> Firing to cone 6 after glazing the bone dry greenware .. Had some
>initial success with 2/3 of the batch coming out great but my luck has
>run out and Im now getting a majority of the pieces with pinholes and what
>Im calling craters...
Try slowing down the early phases of the
firing: the temperatures we would normally
call 'bisque'. Even in a one-shot firing,
you've gotta give things plenty of time to
burn out before the glaze skins over and
traps the outgassing, causing bubbles and
pinholes. Just take it nice and slow to
at least ^05 or thereabouts.
I don't know what temperature that Duncan
Diamond-Clear starts to melt at, but it's
possible that it's low enough that stuff
is still outgassing at temperatures higher
than that. If so, it may not be a suitable
glaze for single-firing, but try a slower-
early-stage firing first, just to see.
-Snail
--
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Checked by AVG Free Edition.
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marci Boskie's Mama =^..^= on tue 20 jun 06
Hey all,
Im hoping some of you might have some answers for me.
Im trying to once-fire porcelain . Ive been using Laguna frost cone
6 and also some slip cast Seeleys Nordic White and a commercial glaze (
duncan's diamond clear) ...
Firing to cone 6 after glazing the bone dry greenware .. Had some
initial success with 2/3 of the batch coming out great but my luck has
run out and Im now getting a majority of the pieces with pinholes and what
Im calling craters. ( look like little volcanoes or hills that you stuck
something into to depress the center ) ...
Ive tried firing hotter ( cone 7) , soaking ( 15 to 90 minutes ) (
the hotter fire and/or the long soak help a little but then the
surface of the glaze orange peels ) . I ve tried thicker glaze, thinner
glaze, very thin coat under a heavier coat, finger polishing the surface
of the clay ( it seems to happen less or rarely on an untouched
slipcast surface ) , making sure I had all the clay dust removed ( I
thought maybe that was it since i did notice that the dry glaze sometimes
had pinholes in it.. but one batch that had no visible pinholes in the dry
glaze still pinholed badly after firing.).. I even tried finger sanding
the dry glaze...
I am basically rolling pieces of clay out with a rolling pin and
trying to leave the surface undisturbed ( since it appears to be worse
if I sand the surface ) or slip casting some parts and doing clay
attachments .. ( the slip cast parts seem to do better with few or no
pinholes ) ....
I would appreciate suggestions .. Thanks
Marci Blattenberger Boskie's Mama =^..^=
http://www.marciblattenberger.com
marci@ppio.com
Porcelain Painters International Online http://www.ppio.com
--
No virus found in this outgoing message.
Checked by AVG Anti-Virus.
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William & Susan Schran User on tue 20 jun 06
On 6/20/06 2:47 AM, "marci Boskie's Mama =^..^=" wrote:
> Firing to cone 6 after glazing the bone dry greenware .. Had some
> initial success with 2/3 of the batch coming out great but my luck has
> run out and Im now getting a majority of the pieces with pinholes and what
> Im calling craters. ( look like little volcanoes or hills that you stuck
> something into to depress the center ) ...
The answer is probably in firing slower through the ^010 - ^04 range, before
the glaze begins to melt and seal the surface, to allow the organics to burn
out, which if not burned out completely, may cause the issue of pinholes and
bubbles/craters.
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
info@flatrockclay.com on tue 20 jun 06
Marci,
I single fire my ^6 translucent porcelain with Spectrum or Amaco glazes very slow going up 25-50 degrees an hour for the first 500 degrees and still remain a little slower than a traditional bisque so that all the organics can burn out because it is very hard to get them out from under the glazes that often have already begun to melt a little. I will remain slower through the 1900 and then resume a more traditional glaze firing after that wit up to a 20 min soak at ^5. You are prob getting better results from your slip work due to the fact that it is often thinner than the handbuilt works and therefor there is less claybody for the organics to outgas through.
I hope this helps and Happy mud fingers,
Kelley Wilks
Flat Rock Clay
Supplies & Gallery
2002 S School Ave
Fayetteville, AR 72701
479-521-3181
Leave a message, our hands may be in mud!
www.flatrockclay.com
"marci Boskie's Mama =^..^=" wrote: Hey all,
Im hoping some of you might have some answers for me.
Im trying to once-fire porcelain . Ive been using Laguna frost cone
6 and also some slip cast Seeleys Nordic White and a commercial glaze (
duncan's diamond clear) ...
Firing to cone 6 after glazing the bone dry greenware .. Had some
initial success with 2/3 of the batch coming out great but my luck has
run out and Im now getting a majority of the pieces with pinholes and what
Im calling craters. ( look like little volcanoes or hills that you stuck
something into to depress the center ) ...
Ive tried firing hotter ( cone 7) , soaking ( 15 to 90 minutes ) (
the hotter fire and/or the long soak help a little but then the
surface of the glaze orange peels ) . I ve tried thicker glaze, thinner
glaze, very thin coat under a heavier coat, finger polishing the surface
of the clay ( it seems to happen less or rarely on an untouched
slipcast surface ) , making sure I had all the clay dust removed ( I
thought maybe that was it since i did notice that the dry glaze sometimes
had pinholes in it.. but one batch that had no visible pinholes in the dry
glaze still pinholed badly after firing.).. I even tried finger sanding
the dry glaze...
I am basically rolling pieces of clay out with a rolling pin and
trying to leave the surface undisturbed ( since it appears to be worse
if I sand the surface ) or slip casting some parts and doing clay
attachments .. ( the slip cast parts seem to do better with few or no
pinholes ) ....
I would appreciate suggestions .. Thanks
Marci Blattenberger Boskie's Mama =^..^=
http://www.marciblattenberger.com
marci@ppio.com
Porcelain Painters International Online http://www.ppio.com
Flat Rock Clay
Supplies & Gallery
2002 S School Ave
Fayetteville, AR 72701
479-521-3181
Leave a message, our hands may be in mud!
www.flatrockclay.com
Snail Scott on tue 20 jun 06
At 01:47 AM 6/20/2006 -0500, you wrote:
> Firing to cone 6 after glazing the bone dry greenware .. Had some
>initial success with 2/3 of the batch coming out great but my luck has
>run out and Im now getting a majority of the pieces with pinholes and what
>Im calling craters...
Try slowing down the early phases of the
firing: the temperatures we would normally
call 'bisque'. Even in a one-shot firing,
you've gotta give things plenty of time to
burn out before the glaze skins over and
traps the outgassing, causing bubbles and
pinholes. Just take it nice and slow to
at least ^05 or thereabouts.
I don't know what temperature that Duncan
Diamond-Clear starts to melt at, but it's
possible that it's low enough that stuff
is still outgassing at temperatures higher
than that. If so, it may not be a suitable
glaze for single-firing, but try a slower-
early-stage firing first, just to see.
-Snail
John Rodgers on tue 20 jun 06
I find that a long slow bisque fire works best for me for porcelain. I
recently had a big project in which I used both slip and pugged clay -
in this case C-5 B-mix. I planned to used the same glaze on both the
pugged clay and the slip, and had concerned about how the glaze would
perform on slip-cast B-mix vs thrown B-mix. In our discussions Laguna
told me that the slip cast piece would be more dense than the pieces
made from pugged clay. This difference could well have effects on the
way the clay out-gases during bisque and glaze firings.
Regards,
John Rodgers
Chelsea, AL - where an electrical storm is approaching, and I have come
in to turn off the computer and get my wooden chair, lantern, and book
into the middle of the room.
marci Boskie's Mama =^..^= wrote:
> Hey all,
> Im hoping some of you might have some answers for me.
> Im trying to once-fire porcelain . Ive been using Laguna frost cone
> 6 and also some slip cast Seeleys Nordic White and a commercial
> glaze (
> duncan's diamond clear) ...
> Firing to cone 6 after glazing the bone dry greenware .. Had some
> initial success with 2/3 of the batch coming out great but my luck has
> run out and Im now getting a majority of the pieces with pinholes and
> what
> Im calling craters. ( look like little volcanoes or hills that you stuck
> something into to depress the center ) ...
> Ive tried firing hotter ( cone 7) , soaking ( 15 to 90 minutes ) (
> the hotter fire and/or the long soak help a little but then the
> surface of the glaze orange peels ) . I ve tried thicker glaze, thinner
> glaze, very thin coat under a heavier coat, finger polishing the
> surface
> of the clay ( it seems to happen less or rarely on an untouched
> slipcast surface ) , making sure I had all the clay dust removed ( I
> thought maybe that was it since i did notice that the dry glaze
> sometimes
> had pinholes in it.. but one batch that had no visible pinholes in the
> dry
> glaze still pinholed badly after firing.).. I even tried finger sanding
> the dry glaze...
> I am basically rolling pieces of clay out with a rolling pin and
> trying to leave the surface undisturbed ( since it appears to be worse
> if I sand the surface ) or slip casting some parts and doing clay
> attachments .. ( the slip cast parts seem to do better with few or no
> pinholes ) ....
> I would appreciate suggestions .. Thanks
>
> Marci Blattenberger Boskie's Mama =^..^=
> http://www.marciblattenberger.com
> marci@ppio.com
> Porcelain Painters International Online http://www.ppio.com
>
>
> --
> No virus found in this outgoing message.
> Checked by AVG Anti-Virus.
> Version: 7.1.394 / Virus Database: 268.9.0/368 - Release Date: 6/16/2006
>
> ______________________________________________________________________________
>
> 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.
>
>
Tony Ferguson on tue 20 jun 06
Bill's right on the money here. This has been my exact experience and remedy to the fault.
Tony Ferguson
William & Susan Schran User wrote:
On 6/20/06 2:47 AM, "marci Boskie's Mama =^..^=" wrote:
> Firing to cone 6 after glazing the bone dry greenware .. Had some
> initial success with 2/3 of the batch coming out great but my luck has
> run out and Im now getting a majority of the pieces with pinholes and what
> Im calling craters. ( look like little volcanoes or hills that you stuck
> something into to depress the center ) ...
The answer is probably in firing slower through the ^010 - ^04 range, before
the glaze begins to melt and seal the surface, to allow the organics to burn
out, which if not burned out completely, may cause the issue of pinholes and
bubbles/craters.
-- 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.
Tony Ferguson
...where the sky meets the lake...
Duluth, Minnesota
Artist, Educator, Web Meister
fergyart@yahoo.com
fergy@cpinternet.com
(218) 727-6339
http://www.aquariusartgallery.com
http://www.tonyferguson.net
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