Carole Fox on mon 13 oct 08
Woe is me. I searched the archives for dunting cures and could not find =
any.
I thought I finally found the replacement for my floating blue, but =
NOOOOO.... this glaze does not fit my clay. My initial tests seemed =
fine- tested on real pieces, not just tiles.=20
Well, perhaps I glazed this batch a bit on the thick side, but of course =
when I glazed a kiln load of hand-carved lidded jars...ping. ping! I =
hear a ping or two every hour. And no, I did not unload the kiln while =
it was still hot.
The glaze, so kindly shared by Anne D. is:
------------------------------------
Recipe Name: my FB=20
Cone: 6 Color: multiphase blue
Firing: Oxidation Surface: Glossy
Amount Ingredient
33 Frit--Ferro 3134
30 Nepheline Syenite
17 Kaolin--EPK
16 Silica
4 Talc
100 Total
Additives
1 Cobalt Oxide
2 Iron Oxide--Red
4 Rutile
2 Bentonite
Unity Oxide
.37 Na2O
.055 K2O
.112 MgO
.463 CaO
1.000 Total
.474 Al2O3
.395 B2O3
.003 Fe2O3
3.575 SiO2
.002 TiO2
.001 P2O5
7.5 Ratio
74.5 Exp
I use Standard 551 cone 6 porcelain.=20
How do I begin to fix this so that it will fit my clay?=20
Carole Fox
Silver Fox Pottery
Elkton, MD
silverfoxpottery@comcast.net
Steve Slatin on tue 14 oct 08
Carole --
I work your formula to have a calculated
COE/CTE of 76.86 -- this will fit some
clay bodies, but if you're using something
like B-Mix, it will likely craze. Pinging
can come from crazing. Dunting usually
leaves a sharp edge at the crack where
crazing will not have much 'feel' to it=20
-- just a light tap as you cross the gap.
You could try to replace some of your
high-expansion material -- the Nepheline
Syenite, or the Frit 3134 -- with Spodumene,
these subs usually work OK on a 1 for 1 basis,
but over 5% you may see a change in result,
either color or surface effects. I have
sometimes had it work at 10% of the total glaze.
=20
You also have to make sure that you're getting
the right undercolor -- I'd expect a caramel
brown -- which will come with keeping the boron
and calcium at nearly the same levels.
This is a quick guess at a solution -- I use
Frit 3195 to get the boron level right with
a smaller amount of frit, lower the Nepheline
Syenite also for expansion, add spodumene to
raise the alkali level and to use the more
powerful lithium to make up for the loss in
fluxes overall, drop the EPK to=20
get the alumina back in the right range,=20
etc. etc.
I do not know if this will work; if it doesn't
it'll probably still not ping even if you have
to add some of the Nepheline Syenite back in
to get it melting the same as it did before.
The COE/CTE is 67.18, so on some clays, this
will indeed dunt -- but not on a porcelainous
stoneware, I suspect. And if it makes a good
melt, it's got the right relationships so you'll
probably get a good floating blue.
Recipe Name: Floating Blue -- Anne D. Altered
Cone: 6 Color: =20
Firing: Oxidation Surface: Glossy
Amount Ingredient
5 Spodumene--Gwalia
25 Nepheline Syenite
8 Kaolin--EPK
20 Silica
8 Talc
32 Frit--Ferro 3195
4 Rutile
2 Iron Oxide--Red
2 Bentonite
1 Cobalt Oxide
107 Total
Unity Oxide
.054 Li2O
.306 Na2O
.053 K2O
.262 MgO
.325 CaO
1.000 Total
.592 Al2O3
.452 B2O3
.057 Fe2O3
4.374 SiO2
.201 TiO2
0 P2O5
7.4 Ratio
67.2 Exp
Comments: From Carole Fox from Anne D. This is an interesting floating bl=
ue; it has a much lower Si/Al ratio than is common for rutile blues. =20
-----------------------------------
Calculations by GlazeMaster=E2=84=A2
www.masteringglazes.com
------------------------------------
Best wishes -- Steve S
--- On Mon, 10/13/08, Carole Fox wrote:
> Woe is me. I searched the archives for dunting cures and
> could not find any.
>=20
> I thought I finally found the replacement for my floating
> blue, but NOOOOO.... this glaze does not fit my clay. My
> initial tests seemed fine- tested on real pieces, not just
> tiles.=20
>=20
> Well, perhaps I glazed this batch a bit on the thick side,
> but of course when I glazed a kiln load of hand-carved
> lidded jars...ping. ping! I hear a ping or two every hour.
> And no, I did not unload the kiln while it was still hot.
>=20
> The glaze, so kindly shared by Anne D. is:
> ------------------------------------
> Recipe Name: my FB=20
>=20
> Cone: 6 Color: multiphase blue
> Firing: Oxidation Surface: Glossy
>=20
> Amount Ingredient
> 33 Frit--Ferro 3134
> 30 Nepheline Syenite
> 17 Kaolin--EPK
> 16 Silica
> 4 Talc
>=20
> 100 Total
>=20
> Additives
> 1 Cobalt Oxide
> 2 Iron Oxide--Red
> 4 Rutile
> 2 Bentonite
>=20
> Unity Oxide
> .37 Na2O
> .055 K2O
> .112 MgO
> .463 CaO
> 1.000 Total
>=20
> .474 Al2O3
> .395 B2O3
> .003 Fe2O3
>=20
> 3.575 SiO2
> .002 TiO2
> .001 P2O5
>=20
> 7.5 Ratio
> 74.5 Exp
>=20
> I use Standard 551 cone 6 porcelain.=20
>=20
> How do I begin to fix this so that it will fit my clay?=20
>=20
> Carole Fox
> Silver Fox Pottery
> Elkton, MD
> silverfoxpottery@comcast.net=0A=0A=0A
Ivor and Olive Lewis on wed 15 oct 08
Dear Carole Fox,
You may get a successful outcome if you do a simple line blend of your
original glaze with one of the Lithium Minerals. My preference , which
cured the same problem with glazes based on Soda Felspar (12% Na2O),
would be to use Petalite. Though this substance has the lowest
proportion of Li2O it is higher by a couple of moles in Silica,
another compound that has an ability to alter CoE.
Or you may wish to use Lepidolite or Spodumene. Amblygonite has the
potential to introduce undesirable elements,
Hope you get a cure.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
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