Heather Bessey on mon 12 sep 11
The transparent green glaze I am using looks very blue. I am firing to cone=
=3D
six using a slow cooling program.Using Laguna clay #60 or #80The recipe:Tr=
=3D
ansparent Green Don Goodrich custer 38.1dolomite 10EPK =
=3D
9.6silica 9.5gersley borate 9.5zinc oxide 9.4 copper ca=
=3D
rb 4.4 Could this be turning blue from the other glazes in the kiln o=
=3D
r from the slow cooling program?I assume the copper is too high for this to=
=3D
be food safe.I would like to find a transparent green that is food safe an=
=3D
d does not turn blue.Heather =
=3D
Ron Roy on tue 13 sep 11
Hi Heather,
I think the term food safe is inappropriate in this case - durable or
stable would be a better description.
Not sure if I have the right recipe - it only totals 86.1.
If that is the right - as you can see - the SiO2 is only 1.99 - it has
to be over 2.5 to begin to be a stable glaze - with 4.4 copper carb it
will leach copper into food and will probably change colour as well -
leave some vinegar in a pot lined with this glaze for a few hours and
see.
CUSTER SPAR................. 38.10
DOLOMITE.................... 10.00
EPK......................... 9.60
SILICA...................... 9.50
GERS BOR Laguna 06/11....... 9.50
ZINC Oxide.................. 9.40
=3D=3D=3D=3D=3D=3D=3D=3D=3D
86.10
CaO 0.30*
MgO 0.18*
K2O 0.12*
Na2O 0.08*
ZnO 0.33*
Fe2O3 0.00
TiO2 0.00
B2O3 0.15
Al2O3 0.29
SiO2 1.99
P2O5 0.00
Si:Al: 6.97
SiB:Al: 7.48
Thermal Expansion: 515.82
Formula Weight: 226.43
Quoting Heather Bessey :
> The transparent green glaze I am using looks very blue. I am firing
> to cone six using a slow cooling program.Using Laguna clay #60 or
> #80The recipe:Transparent Green Don Goodrich custer
> 38.1dolomite 10EPK 9.6silica 9.5gersley
> borate 9.5zinc oxide 9.4 copper carb 4.4 Could this
> be turning blue from the other glazes in the kiln or from the slow
> cooling program?I assume the copper is too high for this to be food
> safe.I would like to find a transparent green that is food safe and
> does not turn blue.Heather
Chic Lotz on wed 14 sep 11
Hi Heather,
I'm not sure why your glaze is turning blue, but if you want a
transparent green glaze, start with a clear glossy glaze and add
increments of copper carb......... the more copper, the darker the
green. If it's for food surfaces definitely do not go over 5% copper
carb. When you get one you like, be sure to test it to see if the
color and sheen hold up to lemon, vinegar and dishwashers.
Here is a stable clear glaze if you want to use it.
Hansen's 5/20
20 Custer Feldspar
20 Frit 3134
20 Silica
20 Epk Kaolin
20 Wollastonite
Good luck!
Chic Lotz
Chic@PotteryPoet.com
www.PotteryPoet.com
www.GlazeBasics.com
Alisa Liskin Clausen on fri 16 sep 11
Hi Heather
I agree with Chic that Hansen 20/20 is good workhorse glaze for coloring.
However, I have found that sometimes the addition of Cu. Carb. can cause
some crazing and I have nothing else to tell about that except my visual
observation.
Additionally on my site, there are several good clears for coloring, such a=
s
Dolita base or even a
commercial base you may like to work with. www.alisapots.dk
I have become a fan of green stains to obtain green in clears. You can
experiment with increments between 1 to 12 percent.
Best regards, Alisa in Denmark
Date: Wed, 14 Sep 2011 07:53:30 -0700
From: Chic Lotz
Subject: Transparent green glaze
Hi Heather,
I'm not sure why your glaze is turning blue, but if you want a
transparent green glaze, start with a clear glossy glaze and add
increments of copper carb......... the more copper, the darker the
green. If it's for food surfaces definitely do not go over 5% copper
carb. When you get one you like, be sure to test it to see if the
color and sheen hold up to lemon, vinegar and dishwashers.
Here is a stable clear glaze if you want to use it.
Hansen's 5/20
20 Custer Feldspar
20 Frit 3134
20 Silica
20 Epk Kaolin
20 Wollastonite
Good luck!
Chic Lotz
Chic@PotteryPoet.com
www.PotteryPoet.com
www.GlazeBasics.com
----------
Don Goodrich on sat 17 sep 11
Hi Heather,
I don't think I've ever used that recipe you quoted, although
I probably collected it from Clayart several years ago.=3D20
Ron's right about the percentages. I wouldn't expect it to pass
the vinegar test.=3D20
Here's a glaze I've been using for the last few years, that
does pass the acid test, and is a glossy transparent green or blue,
depending on what you add:
HONEY GLAZE BASE ^6 oxidation
Custer feldspar=3D09 20
Gerstley borate=3D09 20
Nepheline syenite 20
Flint=3D09 15
Wollastonite 10
Dolomite=3D09 2
EPK kaolin 5
Red iron oxide 2 (Leave out the RIO if you don't care for red speckles)
Titanium dioxide 1
----------------------
TOTAL 95 (because I took out 5% of the original recipe's ir=
=3D
on)
For green, add Cobalt carbonate 0.5 or even less,
Copper carbonate 3.0
For Blue, add Cobalt carbonate 1.0
Copper carbonate 2.5
The Alumina:Silica ratio is 1.00:8.32, which seems to be adequate in thi=
=3D
s case.
here's a photo of it; the upper portion is the blue version, lower is
the green:
http://dongoodrichpottery.com/APC/11APC3Vase.JPG.htm
and it's on the lid and lower part of this jar:
http://dongoodrichpottery.com/APC/11APCcjdh2.JPG.htm
This evolved from a recipe attributed to Kurt Weiser, although when I ask=
=3D
ed
him about it a few years back he didn't recollect it. It might be an old
recipe from Kansas City Art Institute.
Whatever the case, it's a very responsive glaze when sprayed on porcela=
=3D
in=3D20
(I use Standard 365). It's quite sensitive to thickness or texture. If yo=
=3D
u do=3D20
surfaces with chattering, or use a Steve Tool, stamps or carving, this wi=
=3D
ll=3D20
emphasize them.=3D20
I haven't used it much on stoneware, but would expect a bit less brightne=
=3D
ss.
Hope this helps. Good luck.
Don Goodrich
http://dongoodrichpottery.com/
Ron Roy on mon 19 sep 11
Hi Don,
The expansion is a bit high - I reformed it to be more durable as well
- let me know if it's still transparent will you?
CUSTER SPAR................. 22.00
GERS BOR Laguna 06/11....... 22.00
NEPH SY..................... 11.00
SILICA...................... 22.00
Wollastonite................ 10.00
DOLOMITE.................... 3.00
EPK......................... 10.00
=3D=3D=3D=3D=3D=3D=3D=3D=3D
100.00
CaO 0.62*
MgO 0.14*
K2O 0.09*
Na2O 0.15*
Fe2O3 0.01
TiO2 0.00
B2O3 0.37
Al2O3 0.32
SiO2 2.95
P2O5 0.00
Si:Al: 9.34
SiB:Al: 10.50
Thermal Expansion: 439.57 << original was close to 500
Formula Weight: 294.48
RR
Quoting Don Goodrich :
> Hi Heather,
> I don't think I've ever used that recipe you quoted, although
> I probably collected it from Clayart several years ago.
>
> Ron's right about the percentages. I wouldn't expect it to pass
> the vinegar test.
>
> Here's a glaze I've been using for the last few years, that
> does pass the acid test, and is a glossy transparent green or blue,
> depending on what you add:
>
> HONEY GLAZE BASE ^6 oxidation
> Custer feldspar 20
> Gerstley borate 20
> Nepheline syenite 20
> Flint 15
> Wollastonite 10
> Dolomite 2
> EPK kaolin 5
> Red iron oxide 2 (Leave out the RIO if you don't care for red speckles)
> Titanium dioxide 1
> ----------------------
> TOTAL 95 (because I took out 5% of the original recipe's ir=
on)
>
> For green, add Cobalt carbonate 0.5 or even less,
> Copper carbonate 3.0
>
> For Blue, add Cobalt carbonate 1.0
> Copper carbonate 2.5
>
> The Alumina:Silica ratio is 1.00:8.32, which seems to be adequate
> in this case.
>
> here's a photo of it; the upper portion is the blue version, lower is
> the green:
> http://dongoodrichpottery.com/APC/11APC3Vase.JPG.htm
> and it's on the lid and lower part of this jar:
> http://dongoodrichpottery.com/APC/11APCcjdh2.JPG.htm
>
> This evolved from a recipe attributed to Kurt Weiser, although when I ask=
ed
> him about it a few years back he didn't recollect it. It might be an old
> recipe from Kansas City Art Institute.
>
> Whatever the case, it's a very responsive glaze when sprayed on porcela=
in
> (I use Standard 365). It's quite sensitive to thickness or texture. If yo=
u do
> surfaces with chattering, or use a Steve Tool, stamps or carving, this wi=
ll
> emphasize them.
> I haven't used it much on stoneware, but would expect a bit less brightne=
ss.
>
> Hope this helps. Good luck.
>
> Don Goodrich
>
> http://dongoodrichpottery.com/
>
Michael Wendt on tue 20 sep 11
What scale is this COE listed.
In physics we used CTE
Coefficient of Thermal Expansion)
numbers as follows:
5.98 X 10^-6 for example.
Just curious
Michael Wendt
Ron Roy wrote:
Hi Don,
The expansion is a bit high - I reformed it to be more
durable as well
- let me know if it's still transparent will you?
CUSTER SPAR................. 22.00
GERS BOR Laguna 06/11....... 22.00
NEPH SY..................... 11.00
SILICA...................... 22.00
Wollastonite................ 10.00
DOLOMITE.................... 3.00
EPK......................... 10.00
=3D=3D=3D=3D=3D=3D=3D=3D=3D
100.00
CaO 0.62*
MgO 0.14*
K2O 0.09*
Na2O 0.15*
Fe2O3 0.01
TiO2 0.00
B2O3 0.37
Al2O3 0.32
SiO2 2.95
P2O5 0.00
Si:Al: 9.34
SiB:Al: 10.50
Thermal Expansion: 439.57 << original was close
to 500
Formula Weight: 294.48
Ron Roy on wed 21 sep 11
Hi Michael,
x 10-6/C
See chapter 5 in our book - you will see actual measurements compared
to calculated expansions by three different methods for each of the 5
glazes meant to find expansion rates of clays.
RR
Quoting Michael Wendt :
> What scale is this COE listed.
> In physics we used CTE
> Coefficient of Thermal Expansion)
> numbers as follows:
> 5.98 X 10^-6 for example.
> Just curious
> Michael Wendt
>
>
>
> Ron Roy wrote:
> Hi Don,
>
> The expansion is a bit high - I reformed it to be more
> durable as well
> - let me know if it's still transparent will you?
>
> CUSTER SPAR................. 22.00
> GERS BOR Laguna 06/11....... 22.00
> NEPH SY..................... 11.00
> SILICA...................... 22.00
> Wollastonite................ 10.00
> DOLOMITE.................... 3.00
> EPK......................... 10.00
> =3D=3D=3D=3D=3D=3D=3D=3D=3D
> 100.00
>
> CaO 0.62*
> MgO 0.14*
> K2O 0.09*
> Na2O 0.15*
> Fe2O3 0.01
> TiO2 0.00
> B2O3 0.37
> Al2O3 0.32
> SiO2 2.95
> P2O5 0.00
>
> Si:Al: 9.34
> SiB:Al: 10.50
> Thermal Expansion: 439.57 << original was close
> to 500
> Formula Weight: 294.48
>
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