Ian Currie on thu 28 dec 00
Greetings
A few comments on this interesting glaze, and also a question.
Firstly, as several have noted, the colour results from the interaction of
cobalt and titanium (from titanium dioxide or rutile) in a wide range of
glazes.
It occurs with a wide range of fluxes, but as Craig Martell has implied, the
balance of alumina and silica is important. In fact with this particular
colour, it is crucial. This makes it a classic candidate for my grid
method, which takes a mix of fluxes and systematically varies alumina and
silica to produce a "grid" of 35 glazes. I've done some grids (stoneware
and midfire) based around Reitz's green, and the colour is typically
restricted to 2 or 3 of the 35.... but the grid finds the best spot.
Reitz's green by the way is more or less a nepheline syenite shino recipe
with cobalt and rutile added.
This brings me to my question: Has anyone seen a cobalt-titanium green
where the green is shiny? In all the examples that I have examined, the
green is crystalline (small crystals easily seen in a magnifier) and matt.
If the glaze goes shiny, you lose the green.... [although you can easily get
green matt crystal spots in a shiny background.] This means that the
cooling cycle is going to be important, because it is as the glaze cools
that the crystals grow... sometimes hundreds of degrees below top
temperature. So one can try slowing the cooling cycle to grow the green
crystals.
Also for the record, all the cobalt-titanium greens I have seen are in high
alumina glazes - the high alumina coming from high clay or in the case of
Reitz's green high nepheline syenite and clay.
There are some cobalt-titanium greens illustrated in my new book "Revealing
Glazes - Using the Grid Method". You can see a copy of one of these pages
at this URL:
http://ian.currie.to/books/revealing/page82.html
Photo K is a teabowl by Hank Murrow showing his Reitz green....
see also F on page 70 in the book.
Regards
Ian Currie
P.S. If you would like to know more about my glaze method workshops, or if
you would like to purchase one of my books, go to:
http://ian.currie.to/
or just e-mail me. If you pay for the books by credit card at my web site,
they usually take about a week to arrive.
Incidentally, the value of Australian currency is currently way down, so the
book price to you is also down. All prices quoted at my website are in
Aussie dollars.
Cantello Studios on thu 28 dec 00
Just a note, yes I have seen a shine green from this combo. A young potter
friend has been getting this color when he brushes a cobalt wash over his
glaze that has rutile in a glaze that is half G.borate some epk and Sio2.
This is a cone 6 OX. Glaze but the green is there. This makes me question
all the talk about the need for the high alumina in the base. Just thinking
this glaze seams to be as mysterious as a Chrome Tin Pink? Any one out there
have that one at cone 11. That I would like to test. Chris: Soon to be at
Cantellostudios.com give me 60 days that's the plan anyway.
-----Original Message-----
From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG]On
Behalf Of Ian Currie
Sent: Thursday, December 28, 2000 9:51 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Cobalt-Titanium Green
Greetings
A few comments on this interesting glaze, and also a question.
Firstly, as several have noted, the colour results from the interaction of
cobalt and titanium (from titanium dioxide or rutile) in a wide range of
glazes.
It occurs with a wide range of fluxes, but as Craig Martell has implied, the
balance of alumina and silica is important. In fact with this particular
colour, it is crucial. This makes it a classic candidate for my grid
method, which takes a mix of fluxes and systematically varies alumina and
silica to produce a "grid" of 35 glazes. I've done some grids (stoneware
and midfire) based around Reitz's green, and the colour is typically
restricted to 2 or 3 of the 35.... but the grid finds the best spot.
Reitz's green by the way is more or less a nepheline syenite shino recipe
with cobalt and rutile added.
This brings me to my question: Has anyone seen a cobalt-titanium green
where the green is shiny? In all the examples that I have examined, the
green is crystalline (small crystals easily seen in a magnifier) and matt.
If the glaze goes shiny, you lose the green.... [although you can easily get
green matt crystal spots in a shiny background.] This means that the
cooling cycle is going to be important, because it is as the glaze cools
that the crystals grow... sometimes hundreds of degrees below top
temperature. So one can try slowing the cooling cycle to grow the green
crystals.
Also for the record, all the cobalt-titanium greens I have seen are in high
alumina glazes - the high alumina coming from high clay or in the case of
Reitz's green high nepheline syenite and clay.
There are some cobalt-titanium greens illustrated in my new book "Revealing
Glazes - Using the Grid Method". You can see a copy of one of these pages
at this URL:
http://ian.currie.to/books/revealing/page82.html
Photo K is a teabowl by Hank Murrow showing his Reitz green....
see also F on page 70 in the book.
Regards
Ian Currie
P.S. If you would like to know more about my glaze method workshops, or if
you would like to purchase one of my books, go to:
http://ian.currie.to/
or just e-mail me. If you pay for the books by credit card at my web site,
they usually take about a week to arrive.
Incidentally, the value of Australian currency is currently way down, so the
book price to you is also down. All prices quoted at my website are in
Aussie dollars.
____________________________________________________________________________
__
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.
Tommy Humphries on thu 28 dec 00
The following is the glaze that we use at Marshall Pottery... The green
results are with the addition of 3% cobalt oxide, and 5% titanium dioxide.
In applications where it was sprayed fairly thin it was a high gloss bright
olive green.
Where it was sprayed thicker, it was a dark textured olive gloss, with
blue/green highlights.
Can be a nice robins egg blue where *extremely* thin.
This is oxidation fired to ^6 on Black-Jack SS2 claybody
FELDSPAR (any) 600 * presently using minspar
FLINT 200 MESH 175
BALL CLAY om4 150
#10 WHITING 112
ZINC OXIDE (denzox)112
BARIUM CARB. 36
ULTROX 30
BORAX 25
CMC GUM 3
add 97 gal. water and ball mill for 4 hrs.
* all measurements are in pounds.
Application- spray or dip
singlefire to a HARD cone 6 cone tip should just touch kiln shelf
Hope this helps!
Tommy Humphries
----- Original Message -----
From: "Ian Currie"
To:
Sent: Thursday, December 28, 2000 11:51 AM
Subject: Cobalt-Titanium Green
> Greetings
> This brings me to my question: Has anyone seen a cobalt-titanium green
> where the green is shiny? In all the examples that I have examined, the
> green is crystalline (small crystals easily seen in a magnifier) and matt.
> If the glaze goes shiny, you lose the green.... [although you can easily
get
> green matt crystal spots in a shiny background.] This means that the
> cooling cycle is going to be important, because it is as the glaze cools
> that the crystals grow... sometimes hundreds of degrees below top
> temperature. So one can try slowing the cooling cycle to grow the green
> crystals.
>
> Also for the record, all the cobalt-titanium greens I have seen are in
high
> alumina glazes - the high alumina coming from high clay or in the case of
> Reitz's green high nepheline syenite and clay.
>
> There are some cobalt-titanium greens illustrated in my new book
"Revealing
> Glazes - Using the Grid Method". You can see a copy of one of these pages
> at this URL:
> http://ian.currie.to/books/revealing/page82.html
> Photo K is a teabowl by Hank Murrow showing his Reitz green....
> see also F on page 70 in the book.
>
> Regards
>
> Ian Currie
> P.S. If you would like to know more about my glaze method workshops, or
if
> you would like to purchase one of my books, go to:
> http://ian.currie.to/
> or just e-mail me. If you pay for the books by credit card at my web
site,
> they usually take about a week to arrive.
>
> Incidentally, the value of Australian currency is currently way down, so
the
> book price to you is also down. All prices quoted at my website are in
> Aussie dollars.
>
>
____________________________________________________________________________
__
> 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.
>
Ron Roy on sat 30 dec 00
This reminds me of something. Some potters complain of the floating
blue glaze going green. I have never seen an example but I seem to
remember (I don't have the recipe with me) that the alumina is high
as are the alkalies and it is coloured with cobalt and rutile plus
some iron if I recall.
If somebody will post an example of that glaze that does go green I
will post the molecular formula - it may add some light.
RR
>This brings me to my question: Has anyone seen a cobalt-titanium green
>where the green is shiny? In all the examples that I have examined, the
>green is crystalline (small crystals easily seen in a magnifier) and matt.
>If the glaze goes shiny, you lose the green.... [although you can easily get
>green matt crystal spots in a shiny background.] This means that the
>cooling cycle is going to be important, because it is as the glaze cools
>that the crystals grow... sometimes hundreds of degrees below top
>temperature. So one can try slowing the cooling cycle to grow the green
>crystals.
Ron Roy
93 Pegasus Trail,
Scarborough, Ontario
Canada. M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Steve Burtt on mon 1 jan 01
Hi Ron:
Here's a recipe for Floating Blue. I never had trouble with it going
green until we lost Gerstley. I substituted Laguna Borate and all I get now
is Floating Green. I've moved on to try a couple of Gerstley-free recipes
that I found in the archives, but haven't finished my tests yet. Here's my
old recipe:
Neph Syn 41
Gerstley 17
Frit 3134 13
Flint 18
EPK 11
Red Iron Oxide 2
Cobalt Carb. 1.5
Rutile 4
Steve Burtt
Ocean Springs, Mississippi
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