John Hesselberth on sat 24 nov 01
on 11/24/01 7:55 PM, Rachael Rice at rachaelrice@EROLS.COM wrote:
> I have thrown about 50 bowls out of cone 5 B-Mix and glazed them with a
> cobalt glaze with Randi's Red on top. It gave me a really neat metallic
> look where they overlapped. The cobalt glaze was actually a black glaze
> recipe that I changed the oxides since no one seemed interested in
> buying my black pottery. I tested the glaze when it was black with the
> randi's red over it and it didn't leach for my two day vinegar test so I
> didn't think to test it when I changed the oxides. Well the vinegar
> turned the overlap of the two glazes white. I tried brushing a clear
> glaze over the insides and refired to cone 6 but it didn't stop the
> leaching and I also tried brushing a third coat of clear over the other
> two glazes on my bisque ware and it still leached out with vinegar after
> a day. Is there anything I can do with these 50 bowls to save them?
> Below are my two recipes. Thanks
Hi Rachael,
It sounds like you have already tried the obvious fix so I would say "no"
don't waste any more time on them. I looked at the unity formula of your
cobalt blue recipe and it doesn't look that bad IF the composition of your
Gerstley borate is the same as I assumed--which is very unlikely. Randy's
Red, on the other hand is short of alumina and OK, but on the low side, of
silica. I expect the problem is occurring when some of that copper is
getting into the Randy's Red composition--it might hold iron OK, but no way
would it hold copper.
As a side note, I have become frustrated enough trying to understand
GB-based glazes that I have decided to stop trying. It is so non-uniform
that it is nearly impossible to predict what you will get.
My advice: Take out the hammer, learn from it and move on---preferably with
GB-free glazes.
Regards,
John
Web site: http://www.frogpondpottery.com Email: john@frogpondpottery.com
"The life so short, the craft so long to learn." Chaucer's translation of
Hippocrates, 5th cent. B.C.
Rachael Rice on sat 24 nov 01
I have thrown about 50 bowls out of cone 5 B-Mix and glazed them with a
cobalt glaze with Randi's Red on top. It gave me a really neat metallic
look where they overlapped. The cobalt glaze was actually a black glaze
recipe that I changed the oxides since no one seemed interested in
buying my black pottery. I tested the glaze when it was black with the
randi's red over it and it didn't leach for my two day vinegar test so I
didn't think to test it when I changed the oxides. Well the vinegar
turned the overlap of the two glazes white. I tried brushing a clear
glaze over the insides and refired to cone 6 but it didn't stop the
leaching and I also tried brushing a third coat of clear over the other
two glazes on my bisque ware and it still leached out with vinegar after
a day. Is there anything I can do with these 50 bowls to save them?
Below are my two recipes. Thanks
Rachael
Cobalt Blue
Flint 31.%
Neph Syn 30.0%
GB 21.0%
EPK 10.0%
Whiting 8.0%
Cobalt Oxide 3.0%
Black Copper Oxide 2.5%
Randi's Red
GB 31.7%
Flint 29.7%
Kona F-4 Felspar 19.8%
Talc 13.8%
EPK 5.0%
Red Iron Oxide 15%
Crocus Martis 5.0%
Mike Gordon on sun 25 nov 01
Hi,
I hate to beat a dead horse, BUT....... is this glaze ox.? or red???
Yhanks, Mike Gordon
Marie Tedesco-Folderman on sun 25 nov 01
What is the vinegar test? I was reading "leaching bowls" and am not aware
of this test. I am a newcomer to pottery..have been turning for two years.
I have learned much from this site in the past few weeks...thank you, Marie
KEEP THE FAITH!
_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp
Rachael Rice on sun 25 nov 01
In response to the questions on my leaching bowls it is oxidation fired and the
leach test was filling the bowls with vinegar and leaving the vinegar sitting for 2
days and examine the glazes for any changes. Lemon juice also works as an acidic
substance.
Rachael
Marie Tedesco-Folderman wrote:
> What is the vinegar test? I was reading "leaching bowls" and am not aware
> of this test. I am a newcomer to pottery..have been turning for two years.
> I have learned much from this site in the past few weeks...thank you, Marie
>
> KEEP THE FAITH!
>
> _________________________________________________________________
> Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp
>
> ______________________________________________________________________________
> 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.
Martin Howard on mon 26 nov 01
Thanks John for that simple test. I will do it with my current bowls which
are 2% Copper Oxide slip under a clear glaze; then compare with just a 2%
CuO glaze.
If my idea is right about protecting the colouring oxides within the slip,
there should be quite a difference.
Martin Howard
Webbs Cottage Pottery
Woolpits Road, Great Saling
BRAINTREE, Essex CM7 5DZ
01371 850 423
martin@webbscottage.co.uk
http://www.webbscottage.co.uk
This web-site is being updated NOW!
John Hesselberth on mon 26 nov 01
on 11/25/01 12:12 PM, Marie Tedesco-Folderman at mariespotworks@HOTMAIL.COM
wrote:
> What is the vinegar test? I was reading "leaching bowls" and am not aware
> of this test. I am a newcomer to pottery..have been turning for two years.
> I have learned much from this site in the past few weeks...thank you, Marie
>
Hi Marie,
The vinegar test is a good screening test to tell you whether or not your
glaze is grossly unstable. You take a test tile, clean it thoroughly with
soap and water and soak half of it in white or cider vinegar for 3 days.
Then rinse the tile, dry it and let it air dry for another few minutes. If
the glaze color has changed you have a glaze that is really not suitable for
functional work. If the sheen has changed, but not the color it may be OK
or it may not be. further testing is warranted. If neither the sheen or
the color change then it is probably stable--certainly stable enough to
warrant further testing such as leach testing to find out for sure how good
it is. If all of us would vinegar test every glaze we try we would weed out
some of these terrible glazes that are floating around and being used on
functional work.
Regards,
John
Web site: http://www.frogpondpottery.com Email: john@frogpondpottery.com
"The life so short, the craft so long to learn." Chaucer's translation of
Hippocrates, 5th cent. B.C.
Cl Litman on mon 26 nov 01
John,
Have a stupid question. Once the nasty stuff is leached out of the bowls
(ie treat all the bowls), what's the harm in using them?
Do you feel the glaze surface would still be unstable?
Cheryl Litman - NJ
cheryllitman@juno.com
On Mon, 26 Nov 2001 14:11:31 -0500 John Hesselberth
writes:
> on 11/25/01 12:12 PM, Marie Tedesco-Folderman at
> mariespotworks@HOTMAIL.COM
> wrote:
>
> > What is the vinegar test? I was reading "leaching bowls" and am
> not aware
> > of this test. I am a newcomer to pottery..have been turning for
> two years.
> > I have learned much from this site in the past few weeks...thank
> you, Marie
> >
> Hi Marie,
>
> The vinegar test is a good screening test to tell you whether or not
> your
> glaze is grossly unstable. You take a test tile, clean it
> thoroughly with
> soap and water and soak half of it in white or cider vinegar for 3
> days.
> Then rinse the tile, dry it and let it air dry for another few
> minutes. If
> the glaze color has changed you have a glaze that is really not
> suitable for
> functional work. If the sheen has changed, but not the color it may
> be OK
> or it may not be. further testing is warranted. If neither the
> sheen or
> the color change then it is probably stable--certainly stable enough
> to
> warrant further testing such as leach testing to find out for sure
> how good
> it is. If all of us would vinegar test every glaze we try we would
> weed out
> some of these terrible glazes that are floating around and being
> used on
> functional work.
>
> Regards,
>
> John
John Hesselberth on tue 27 nov 01
on 11/26/01 7:11 PM, Cl Litman at cheryllitman@JUNO.COM wrote:
> Have a stupid question. Once the nasty stuff is leached out of the bowls
> (ie treat all the bowls), what's the harm in using them?
>
> Do you feel the glaze surface would still be unstable?
>
> Cheryl Litman - NJ
Cheryl,
Once the nasty stuff is leached out, the glaze probably won't have any
color, it will have a rough surface, etc. You aren't just leaching out a
few molecules of some theoretical bad guy. You are often dissolving
significant fractions of the glaze. It is a question of durability and
suitability for intended use. I have a couple mugs, made by other potters,
that have a rough, pitted, colorless surface on the inside. These are
garbage glazes and the potters who made and sold them should be ashamed of
them regardless of whether or not anyone was harmed by them.
Regards,
John
Web site: http://www.frogpondpottery.com Email: john@frogpondpottery.com
"The life so short, the craft so long to learn." Chaucer's translation of
Hippocrates, 5th cent. B.C.
Cindy Strnad on tue 27 nov 01
You know,
By the time you
a) fill all the bowls with vinegar/muratic
acid/whatever and let them sit for a week or so
b) clean all the bowls
c) reglaze all the bowls so they'll be pretty and
smooth
d) refire all the bowls
e) etcetera
You could have finished up several hundred new
bowls. It's a wrench, but throw them away.
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
cindy@earthen-vessels-pottery.com
http://www.earthen-vessels-pottery.com
claybair on tue 27 nov 01
I agree with Cindy about not wasting you time trying to "fix" those bowls.
But I don't agree that you should throw them away.
They can be saved....
just turn them into garden art or mosaics.
Why burden the landfill when you can turn a
mistake into something aesthetic?
Gayle Bair
Bainbridge Island, WA
http://claybair.com
Cindy wrote>>
You know,
By the time you
a) fill all the bowls with vinegar/muratic
acid/whatever and let them sit for a week or so
b) clean all the bowls
c) reglaze all the bowls so they'll be pretty and
smooth
d) refire all the bowls
e) etcetera
You could have finished up several hundred new
bowls. It's a wrench, but throw them away.
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
cindy@earthen-vessels-pottery.com
http://www.earthen-vessels-pottery.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.
| |
|
