Lee Love on mon 3 nov 08
On Mon, Nov 3, 2008 at 11:16 AM, Kate McCoy wrote:
uble free as a glaze gets.
>
> Well, he tried a small batch on a ^6 porcelain (southern Ice style),
> bisqued to 04. The glaze has completely come off. When it dried, if you
> so much as create an air current walking past the pot, the glaze flakes
> and crumbles to dust. There is a ring of dried glaze powder round the
> base of each pot.
These glazes were formulated for a porcelain body? I cannot use my
standard ash glaze (that was formulated for stoneware) on porcelain.
It flakes off at the rim after firing. The shrinkage of the two clay
bodies are different.
--
Lee Love in Minneapolis
http://togeika.multiply.com/journal
http://mashikopots.blogspot.com/
http://claycraft.blogspot.com/
"Let the beauty we love be what we do.
There are hundreds of ways to kneel and kiss the ground." --Rumi
Kate McCoy on mon 3 nov 08
Hello All;
I sent the following message last week, just before Clayart went down.
It didn't make it to the list so am resending, with an update.
------------------------------------------------
Hi,
I have encountered a problem that I hope someone can help with
resolving. Hubby wanted a reliable base glaze to try out some rare earth
colours - in this case, neodymium. So I gave him the recipe of Glossy
Base Glaze 2 (p 96, MC6 Glaze) since Ron and John said it was about as
trouble free as a glaze gets.
Well, he tried a small batch on a ^6 porcelain (southern Ice style),
bisqued to 04. The glaze has completely come off. When it dried, if you
so much as create an air current walking past the pot, the glaze flakes
and crumbles to dust. There is a ring of dried glaze powder round the
base of each pot.
I thought it might be the high proportion of neodymium, but he did
blends around the pots, so I'm not sure what's going on.
Should I make another small batch of glaze, or does this glaze not do
well with porcelain - or WHAT?
Kathy
Olympia, WA
--------------------------------------------------
UPDATE for anyone working with rare earth oxides
Since we were doing a glost on the weekend, we tried mixing up new
batches of glazes for the rare earth colours. We made a Glossy Base 1,
and a new Glossy base 2 - in both cases, the neodymium (even with CMC
gum additions) flakes and crumbled off the pots. HOWEVER, when we tried
the same base glazes with praseodymium and erbium , the glazes were
fine, even without gum.
CONCLUSION - either neodymium is a problematic oxide, or the batch we
have is somehow contaminated.
Any other thoughts anyone!
Kathy - hanging by fingernails waiting for the kiln to cool!
Lynn Goodman Porcelain Pottery on tue 4 nov 08
I thought I sent this out to clayart last night, but it went just to
May. Therefore, here it is:
Hi Kathy and May,
OK, here's my two cents worth:
The rare earth oxides I have used at ^6, neodymium, praseodymium and
erbium, were all very refractory in my glossy base AND caused
extensive crazing. (My glaze doesn't usually craze at all.) I have
been toying with the idea of trying the rare earth oxides again when
I can devote some time to trying to fix these problems, because the
colors are really beautiful-- especially the erbium (pink!).
I have, however, never had the flaking problem that is being
described. I think there may be a problem with the neodymium itself.
If you haven't tried it, I would add in some cmc-- it will give you a
durable coat that will resist flaking, at least until it burns out
during the firing. Between 1/4 of 1% to 1/2 of 1% in the DRY mix (mix
it in well before adding the water, then sieve immediately) should be
enough to harden the glaze coat. It will also help keep the neodymium
from settling out. But you will need to use a little less water in
the glaze, as the cmc lengthens the drying time, making for a thinner
coat.
If you are already using cmc, then I don't know what else to try. I
would probably call up the supplier for help. If they can't help you,
then ask for the manufacturer's contact info-- the manufacturer
should be able to offer suggestions, or replace the neodymium if
there's no workable solution.
Good luck,
Lynn
On Nov 3, 2008, at 11:23 PM, May Luk wrote:
> Hello Kathy;
>
> From what I know rare earth oxides need to fired above cone 8. I
> have used Neodymium (8%) on a high alkaline (with calcium borate
> frit) base glaze and fired to cone 9 on Grolleg porcelain (Standard
> Clay) and there wasn't any problem. Without the rare earth oxide,
> the glaze is really runny. The glaze is a bit more stiff with the
> Neodymium at cone 9.
> My Neodymium was bought in England. I have bought some from US
> pigment but I have not tried the 'domestic' one yet.
> I know that Lynn Goodman has used rare earth oxides on porcelain at
> cone 6 with success. I've bought her bowl. Maybe she will chime in.
>
Lynn Goodman
Fine Porcelain Pottery
Cell 347-526-9805
www.lynngoodmanporcelain.com
May Luk on tue 4 nov 08
Hello Kathy;
From what I know rare earth oxides need to fired above cone 8. I have used =
Neodymium (8%) on a high alkaline (with calcium borate frit) base glaze and=
fired to cone 9 on Grolleg porcelain (Standard Clay) and there wasn't any =
problem. Without the rare earth oxide, the glaze is really runny. The glaze=
is a bit more stiff with the Neodymium at cone 9.
My Neodymium was bought in England. I have bought some from US pigment but =
I have not tried the 'domestic' one yet.
I know that Lynn Goodman has used rare earth oxides on porcelain at cone 6 =
with success. I've bought her bowl. Maybe she will chime in.
Regards
May
Brooklyn NY
[...]
>=20
> I have encountered a problem that I hope someone can help
> with
> resolving. Hubby wanted a reliable base glaze to try out
> some rare earth
> colours - in this case, neodymium. So I gave him the recipe
> of Glossy
> Base Glaze 2 (p 96, MC6 Glaze) since Ron and John said it
> was about as
> trouble free as a glaze gets.
>=20
> Well, he tried a small batch on a ^6 porcelain (southern
> Ice style),
> bisqued to 04. The glaze has completely come off. When it
> dried, if you
> so much as create an air current walking past the pot, the
> glaze flakes
> and crumbles to dust. There is a ring of dried glaze powder
> round the
> base of each pot.
>=20
> I thought it might be the high proportion of neodymium, but
> he did
> blends around the pots, so I'm not sure what's
> going on.
>=20
> Should I make another small batch of glaze, or does this
> glaze not do
> well with porcelain - or WHAT?
>=20
> Kathy
> Olympia, WA
> --------------------------------------------------
>=20
> UPDATE for anyone working with rare earth oxides
>=20
> Since we were doing a glost on the weekend, we tried mixing
> up new
> batches of glazes for the rare earth colours. We made a
> Glossy Base 1,
> and a new Glossy base 2 - in both cases, the neodymium
> (even with CMC
> gum additions) flakes and crumbled off the pots. HOWEVER,
> when we tried
> the same base glazes with praseodymium and erbium , the
> glazes were
> fine, even without gum.
>=20
> CONCLUSION - either neodymium is a problematic oxide, or
> the batch we
> have is somehow contaminated.
>=20
> Any other thoughts anyone!
>=20
> Kathy - hanging by fingernails waiting for the kiln to
> cool!=0A=0A=0A
Ron Roy on wed 12 nov 08
Hi Lee,
They were not formulated for any particular clay body - we used them on two
porcelains and two stoneware clays. We also documented several of them on
both types of clays.
The shrinkage of bisque fired clays does not mater to a glaze - it's the
shrinkage and the drying strength of the glaze that is important.
If you mean shivering off the rim after firing - then that is a completely
different subject and can be addressed by altering the CEO of the glaze -
or the clay.
RR
>These glazes were formulated for a porcelain body? I cannot use my
>standard ash glaze (that was formulated for stoneware) on porcelain.
>It flakes off at the rim after firing. The shrinkage of the two clay
>bodies are different.
>
>--
> Lee Love in Minneapolis
Ron Roy
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
| |
|
