glaze gurus - cobalt green

updated sun 2 jun 02

Valerie Hawkins on wed 29 may 02

What are the factors that push cobalt into the greens? I know rutile is
one, but are there other factors? I especially love RR Saffire where you
have the blue breaking to green. That particular glaze has quite a bit of
rutile, and I know that it goes very green when overfired, but this doesn't
seem to be true of any cobalt glaze with that much rutile.

Thanks,

Valerie

John Post on wed 29 may 02

Here is a glaze that I developed based on Ian's work with the Reitz midfire
green.
I think his original may have had neph. sy in it that I replaced frit 3110.
It fires to a blue and green at cone 6 and does not have any lithium in it.
You can see samples of it fired to cone 6 at this address...
http://www.c3net.net/waverock/potter_info.htm
After cone 6 drops, I let the kiln cool naturally to 1800 degrees F and then
drop at 75 degrees F per hour until I hit 1300. Then I let the kiln cool
naturally again.

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+++ Reitz/Currie Midfire Green (John Post's Variation 1) +++
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Date: 06/23/01

EPK 1320 13.2%
Frit 3110 2170 21.7%
Frit 3134 350 3.5%
Whiting 520 5.2%
Spodumene 870 8.7%
Nepheline syenite 4770 47.7%
-------- ------
10000 100 %

Cobalt carbonate 100 1 %
Rutile 300 3 %

Cost: $ 1.91 per kg glaze
$ 19.07 per 10000 g batch

===========================
Chemical Analysis
===========================

Na2O 0.48 Al2O3 0.66 SiO2 3.27
K2O 0.10 B2O3 0.07 TiO2 0.12
MgO 0.00 Fe2O3 0.01
CaO 0.32
Li2O 0.07
CoO 0.03

Alumina:Silica ratio is 1.00 : 4.96
Neutral:Acid ratio is 1.00 : 4.67
Alkali:Neutral:Acid ratio is 1.00 : 0.73 : 3.39

Expansion coefficient: 89.6 x 10e-7 per degree C
Oxides causing abnormal expansion effects: Li2O B2O3


on 5/29/02 3:37 AM, Valerie Hawkins at vhawkins1@CAROLINA.RR.COM wrote:

> What are the factors that push cobalt into the greens? I know rutile is
> one, but are there other factors?

All the green glazes I've seen from cobalt and rutile have significant
amounts of lithium as well.
Paul Lewing, Seattle

Christena Schafale on wed 29 may 02

I'm not a guru, but I did spend some time trying (and eventually
succeeding) to get a cobalt green. Some things that seem to be true: 1)
avoid any flux materials with magnesia (e.g., talc, dolomite), since they
will push cobalt toward purple rather than green, 2) use about 6% rutile
and about 2% cobalt carb, 3) higher alumina content tends to promote
greens, though too much alumina will turn the glaze blackish, 4) the green
tends to come through when the glaze is thinner, blue where thicker
(although I believe Ian Currie found the opposite with a glaze experiment
he described here once).

Chris


At 07:37 AM 05/29/2002 -0400, you wrote:
>What are the factors that push cobalt into the greens? I know rutile is
>one, but are there other factors? I especially love RR Saffire where you
>have the blue breaking to green. That particular glaze has quite a bit of
>rutile, and I know that it goes very green when overfired, but this doesn't
>seem to be true of any cobalt glaze with that much rutile.
>
>Thanks,
>
>Valerie
>
>___________________________________________________________________________
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Consultation and Referral Specialist
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Dave Finkelnburg on wed 29 may 02

Valerie,
You are on the right track with the titanium.
While I am no guru, I can tell you that Ian Currie, in his excellent
book, "Revealing Glazes," cites "....cobalt and titania (titanium dioxide)
in a high alumina glaze..." are needed for the green color.
I wonder if the "overfired" you refer to actually allows more glaze-clay
body interaction that gets more alumina into the glaze, tipping it toward
the green. I know I use one cobalt matt that goes green when thinly applied
to stoneware.
Here is, by the way, an excellent area to explore using Curie grid
tiles! Good luck! Cobalt greens are so nice.
Dave Finkelnburg in Idaho, impatiently waiting on a cooling kiln.
What do you mean, I have no patience at all?! :-)

From: Valerie Hawkins
Subject: Glaze gurus - cobalt green

>What are the factors that push cobalt into the greens? I know rutile is
>one, but are there other factors? I especially love RR Saffire where you
>have the blue breaking to green. That particular glaze has quite a bit of
>rutile, and I know that it goes very green when overfired, but this doesn't
>seem to be true of any cobalt glaze with that much rutile.

Paul Lewing on wed 29 may 02

on 5/29/02 3:37 AM, Valerie Hawkins at vhawkins1@CAROLINA.RR.COM wrote:

> What are the factors that push cobalt into the greens? I know rutile is
> one, but are there other factors?

All the green glazes I've seen from cobalt and rutile have significant
amounts of lithium as well.
Paul Lewing, Seattle

Jim V Brooks on wed 29 may 02

Valerie.. i don't think it is the rutile that pushes cobalt to green ...but
rather the titanium dioxide/oxide that is a major part of the rutile. I
have gotten greens from Cobalt with 6%+ Titanium dioxide..
Jim in Denton

cd on wed 29 may 02

This usual disclaimer involving guruness..

I attended an Ian Currie workshop at Jeff Lawerence's shop near Espanola =
NM just over a year ago. One of the grids our class did was a ^6 =
derivation of Reitz Green. Of the 35 grid spaces, green appears on only =
six spaces. Two of those being just a whisper.. The highest alumina, =
space 1, is grey black, likewise with space 6, although there is a =
softening of the color.
Spaces 11 and 12 begin to definitely show green, with the strongest =
color being at the thickest application. Spaces 16 and 17 are both =
beautiful cobalt/titanium greens with space 16 being the most brilliant, =
again in the thickest application. Space 17 begins to scatter a small =
amount of blue in the green field, again best in the thickest =
application. Spaces 21 through 35 are all strong cobalt blues without =
any hints of green.
So, the very nicest green appears exactly half way up the alumina =
ladder, at space 16. Less alumina and there is a solid cobalt blue, =
more alumina and we begin to drift towards grey.=20
The Currie method is perfect for this kind of experimentation..becomes =
clear as a bell when studied.

Craig AZ=20

Ian Currie on thu 30 may 02

Hi again Valerie

Me again! You definitely need to understand about the grid method if you
don't already. The essential things are the cobalt and titanium, the latter
from rutile or titanium dioxide. However my experience with grids shows
that the green is fussy about alumina and silica.

If you make a grid around this Corner C glaze (below) you will find some
yummy greens around Glaze 11,16,21 down the left side of the grid, for Cone
6 oxidation....
Corner C for Co/Ti Green:
54 Nepheline Syenite
10 Spodumene
6 Whiting
30 Ferro Frit 3134
+ 1% Cobalt Carbonate
+ 3% Rutile

This is NOT the glaze that will give the green. It is the starting point
glaze from which the grid is generated... If you input this glaze into my
Calculation Page at my web site:
http://ian.currie.to/
... then it will produce 35 glaze recipes... and Recipes No. 11, 16 and 21
should show some good greens. Try the glazes both thick and thin to find
the best combinaton. Thick should be thick!

P.S Just noticed Chris Schafale's contribution (Hi Chris) most of which I
agree with. Fluxes are definitely good to play around with. High feldspar
is good. Also barium helps but is NOT essential.
P.P.S. Wow!!! Just working my way down the list of people contributing to
this thread. Hi Dave, Paul, Craig in AZ and others. Most are well on track
and I think you should have no problem coming up with a Co/Ti green!

Regards

Ian
http://ian.currie.to/

> From: Valerie Hawkins
> Reply-To: Ceramic Arts Discussion List
> Date: Wed, 29 May 2002 07:37:25 -0400
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Glaze gurus - cobalt green
>
> What are the factors that push cobalt into the greens? I know rutile is
> one, but are there other factors? I especially love RR Saffire where you
> have the blue breaking to green. That particular glaze has quite a bit of
> rutile, and I know that it goes very green when overfired, but this
doesn't
> seem to be true of any cobalt glaze with that much rutile.
>
> Thanks,
>
> Valerie

John Post on thu 30 may 02

Hi Paul,

Thanks for pointing out my oversight regarding the lithium. Glazchem shows
it at .07 moles, but this is from the analysis for spodumene that came with
the program. The spodumene that I am using I inherited from a school and I
don't have a specific analysis for it...so I can't be sure how much really
is in the glaze.

John Post
http://www.c3net.net/waverock

> It fires to a blue and green at cone 6 and does not have any lithium in
it.

> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> +++ Reitz/Currie Midfire Green (John Post's Variation 1) +++
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>
> Date: 06/23/01
>
> EPK 1320 13.2%
> Frit 3110 2170 21.7%
> Frit 3134 350 3.5%
> Whiting 520 5.2%
> Spodumene 870 8.7%
> Nepheline syenite 4770 47.7%
> -------- ------
> 10000 100 %
>
> Cobalt carbonate 100 1 %
> Rutile 300 3 %

Actually, John, this glaze does have lithium in it from the spodumene. I
didn't run it through a calculation program, but since LiO2 is so light, I
think you might be surprised how much LiO2 is in there, in a molecular
analysis.
Paul Lewing, Seattle

____________________________________________________________________________
__
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.

iandol on thu 30 may 02

Dear Valerie Hawkins,

It is possible that the inclusion of Zinc Oxide in a recipe would =
enhance the probability of getting a true Cobalt Green. We had an =
extensive discussion about this a couple of years ago. Regarding the use =
of Rutile or Titanium Oxide, my own efforts have produced muted greens =
when there is less than one percent Cobalt Carbonate in the mixture.

Am I correct in assuming you are firing Electric to Cone Six? If so, =
experimentation with one of the RR glazes which incorporates Zinc oxide =
may be profitable.

Enjoy your search.

Best regards,

Ivor Lewis. Redhill, South Australia.

Hank Murrow on thu 30 may 02

>on 5/29/02 5:19 PM, Ian Currie at fcurriap@FLEXI.NET.AU wrote:
>
>> However my experience with grids shows
>> that the green is fussy about alumina and silica.
>>
>> If you make a grid around this Corner C glaze (below) you will find some
>> yummy greens around Glaze 11,16,21 down the left side of the grid, for
Cone
>> 6 oxidation....
>> Corner C for Co/Ti Green:
>> 54 Nepheline Syenite
>> 10 Spodumene
>> 6 Whiting
>> 30 Ferro Frit 3134
>> + 1% Cobalt Carbonate
>> + 3% Rutile
>
>We did this grid in Ian's workshop that I took last fall, and I'll make a
>suggestion here that I made in the workshop, but have never pursued. As
Ian
>points out, the green glazes are all right along the left (low silica) side
>of the grid. So it's possible there might be even greener ones just to the
>left of this, off this grid. That would mean that you'd have to start with
>less silica in the flux set in Corner C. It would be hard to find
>lower-silica fluxes than Neph Sy and whiting, but you could take out some
>silica by substituting lithium carbonate for the spodumene in Corner C.
>This may well give you a new set of problems, as has been extensively
>discussed on this list before, and of course this would mean that the
glazes
>produced over there would have even less silica, so stability could be even
>more of a problem, but you could very well get greener glazes.
>Somebody try it and let us know.
>Paul Lewing, Seattle


Dear Paul;

Have you thought about starting with Alumina in the A corner
instead of Kaolin? Quick way to get more alumina and less silica onto
the grid.

Cheers, Hank

Bobbruch1@AOL.COM on thu 30 may 02

Craig: would you have any of those details of the cone 6 derviation of the
Reitz Green. I used to use the cone 10 Reitz Green when I was in school and
would love to use it in a oxidation environment at lower temps.

Thanks, Bob Bruch

<<<<From: cd
Subject: Re: Glaze gurus - cobalt green

<<<<Espanola
NM just over a year ago. One of the grids our class did was a ^6 derivation
of Reitz Green.