Richard Mahaffey on wed 29 jan 03
Someone mentioned the Japanese style of cobalt called gosu.
Gosu is made from pebbles of cobalt ore containing some manganese. I
have been told that Gosu is hard to get or sometimes impossible to get
in Japan.
Bernard Leach in A Potter's book has a formula for "Chinese Cobalt".
It is:
Manganese oxide 40
Black Iron Oxide 30
Black Cobalt Oxide 20
Calcined Ochre 10
We use it at school on all of our glazes except the mattes and semi
matte glazes. For matte glazes we have had good success with mixing a
little of the glaze with the cobalt oxide to tone it down.
By having the students use Leach's Chinese cobalt you can see that we
save a lot on cobalt.
Rick Mahaffey
Tacoma Community College
Tacoma, Washington, USA
Richard Mahaffey on thu 30 jan 03
Linda, Lily, et al.
The Leach Chinese Cobalt mixture is used to produce a cobalt color that
is very close to the gosu color that was used in Japan. Remember that
Leach was trained in Japan. Gosu is the Japanese name for the natural
cobalt ore pebbles that they ground up for use in decorating pottery.
The gosu pebbles came from China hence Leach's naming his mixture
"Chinese Cobalt".
Cobalt oxide is and has been refered to as "Black Cobalt Oxide" because
it is black when it is in powder form not for the color it makes.
Cobalt carbonate is sometimes called "Pink cobalt" even though it does
not commonly produce a pink color. I have seen "Black" copper oxide as
well even though it rarely produces a balck color in a glaze.
The advantage if "Chinese cobalt" mix is that it requires only 20%
cobalt and produces a much more easily modulated and controlled blue
color.
Leach developed the "Chinese Cobalt" mixture based on what was in the
cobalt ore pebbles that were ground for use in Japan. There was no
copper in the original Gosu.
Rick Mahaffey
Tacoma Community College
Tacoma, Washington , USA
I just picked another copy of "A Potter's Book". This one a Third
American printing from 1948 (First printing from 1946, and the second in
'48 also.) in excellent condition.
I might be persuaded to part with it. If anyone is interested in
owning a copy contact me off the list.
Lee Burningham (Box Elder High School) on thu 30 jan 03
Howdy,
We use a goussou/gosu (sp?) at Box Elder High School for a dark
blue/black in raku and in high-fire applications. The recipe is one from
Andy Watson, equal parts copper carbonate, cobalt oxide, and iron oxide.
Very dark, black going to blue. Works well in salt as well.
Lee Burningham
Subject: Cobalt tricks
Bernard Leach in A Potter's book has a formula for "Chinese Cobalt".
It is:
Manganese oxide 40
Black Iron Oxide 30
Black Cobalt Oxide 20
Calcined Ochre 10
We use it at school on all of our glazes except the mattes and semi
matte glazes. For matte glazes we have had good success with mixing a
little of the glaze with the cobalt oxide to tone it down.
By having the students use Leach's Chinese cobalt you can see that we
save a lot on cobalt.
Rick Mahaffey
Tacoma Community College
Tacoma, Washington, USA
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Linda Knapp on thu 30 jan 03
I am a little confussed as to what you do with this. (Maybe I missed an
email somewhere?) Do you use this in place of Cobalt Carbonate or Oxide
or is this used as an accent? Also I have not heard of Black Cobalt
Oxide - is that a typo? (You can tell I do not have Leach's book to
refer to here)
Linda
Seattle, Washington, USA
Richard Mahaffey wrote:
>Someone mentioned the Japanese style of cobalt called gosu.
>Gosu is made from pebbles of cobalt ore containing some manganese. I
>have been told that Gosu is hard to get or sometimes impossible to get
>in Japan.
>
>Bernard Leach in A Potter's book has a formula for "Chinese Cobalt".
>It is:
>
>Manganese oxide 40
>Black Iron Oxide 30
>Black Cobalt Oxide 20
>Calcined Ochre 10
>
>We use it at school on all of our glazes except the mattes and semi
>matte glazes. For matte glazes we have had good success with mixing a
>little of the glaze with the cobalt oxide to tone it down.
>By having the students use Leach's Chinese cobalt you can see that we
>save a lot on cobalt.
>
>Rick Mahaffey
>Tacoma Community College
>Tacoma, Washington, USA
>
>______________________________________________________________________________
>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.
>
>
Lily Krakowski on thu 30 jan 03
i do not know about black cobalt oxide. Just plain....
Leach among others "complained" that modern cobalt, which, as I understand
it is the byproduct of refining something else, was too pure, created a
glary, vulgar, cold, spit-in-your eye blue. So he added stuff to it; so
have several others. This soften the blue, makes it less shrill. What gosu
means I have no idea. I gather from looking it up on the internet that it
is good old natural unadorned as-found-in-nature cobalt.
I temper my cobalt blue for decoration by mixing it in a solution of my red
clay body.....
Linda Knapp writes:
> I am a little confussed as to what you do with this. (Maybe I missed an
> email somewhere?) Do you use this in place of Cobalt Carbonate or Oxide
> or is this used as an accent? Also I have not heard of Black Cobalt
> Oxide - is that a typo? (You can tell I do not have Leach's book to
> refer to here)
>
> Linda
> Seattle, Washington, USA
>
> Richard Mahaffey wrote:
>
>> Someone mentioned the Japanese style of cobalt called gosu.
>> Gosu is made from pebbles of cobalt ore containing some manganese. I
>> have been told that Gosu is hard to get or sometimes impossible to get
>> in Japan.
>>
>> Bernard Leach in A Potter's book has a formula for "Chinese Cobalt".
>> It is:
>>
>> Manganese oxide 40
>> Black Iron Oxide 30
>> Black Cobalt Oxide 20
>> Calcined Ochre 10
>>
>> We use it at school on all of our glazes except the mattes and semi
>> matte glazes. For matte glazes we have had good success with mixing a
>> little of the glaze with the cobalt oxide to tone it down.
>> By having the students use Leach's Chinese cobalt you can see that we
>> save a lot on cobalt.
>>
>> Rick Mahaffey
>> Tacoma Community College
>> Tacoma, Washington, USA
>>
>> _________________________________________________________________________
>> _____
>> 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.
>>
>>
>
> __________________________________________________________________________
> ____
> 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.
Lili Krakowski
P.O. Box #1
Constableville, N.Y.
(315) 942-5916/ 397-2389
Be of good courage....
Lily Krakowski on fri 31 jan 03
There IS black copper oxide (CuO) and it is pretty black. That is the one
commonly used. There also is red copper oxide (Cu20) which is a lovely
wine color.
Richard Mahaffey writes:
> Linda, Lily, et al.
>
> The Leach Chinese Cobalt mixture is used to produce a cobalt color that
> is very close to the gosu color that was used in Japan. Remember that
> Leach was trained in Japan. Gosu is the Japanese name for the natural
> cobalt ore pebbles that they ground up for use in decorating pottery.
> The gosu pebbles came from China hence Leach's naming his mixture
> "Chinese Cobalt".
>
> Cobalt oxide is and has been refered to as "Black Cobalt Oxide" because
> it is black when it is in powder form not for the color it makes.
> Cobalt carbonate is sometimes called "Pink cobalt" even though it does
> not commonly produce a pink color. I have seen "Black" copper oxide as
> well even though it rarely produces a balck color in a glaze.
>
> The advantage if "Chinese cobalt" mix is that it requires only 20%
> cobalt and produces a much more easily modulated and controlled blue
> color.
>
> Leach developed the "Chinese Cobalt" mixture based on what was in the
> cobalt ore pebbles that were ground for use in Japan. There was no
> copper in the original Gosu.
>
> Rick Mahaffey
> Tacoma Community College
> Tacoma, Washington , USA
>
> I just picked another copy of "A Potter's Book". This one a Third
> American printing from 1948 (First printing from 1946, and the second in
> '48 also.) in excellent condition.
> I might be persuaded to part with it. If anyone is interested in
> owning a copy contact me off the list.
>
> ______________________________________________________________________________
> 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.
Lili Krakowski
P.O. Box #1
Constableville, N.Y.
(315) 942-5916/ 397-2389
Be of good courage....
jeremy Kaiser on fri 31 jan 03
Sorry if this sounds stupid, but I am exhausted from work last night, I take it you mean david leach right?
Jeremy kaiser, the floridian potter
Richard Mahaffey wrote:Linda, Lily, et al.
The Leach Chinese Cobalt mixture is used to produce a cobalt color that
is very close to the gosu color that was used in Japan. Remember that
Leach was trained in Japan. Gosu is the Japanese name for the natural
cobalt ore pebbles that they ground up for use in decorating pottery.
The gosu pebbles came from China hence Leach's naming his mixture
"Chinese Cobalt".
Cobalt oxide is and has been refered to as "Black Cobalt Oxide" because
it is black when it is in powder form not for the color it makes.
Cobalt carbonate is sometimes called "Pink cobalt" even though it does
not commonly produce a pink color. I have seen "Black" copper oxide as
well even though it rarely produces a balck color in a glaze.
The advantage if "Chinese cobalt" mix is that it requires only 20%
cobalt and produces a much more easily modulated and controlled blue
color.
Leach developed the "Chinese Cobalt" mixture based on what was in the
cobalt ore pebbles that were ground for use in Japan. There was no
copper in the original Gosu.
Rick Mahaffey
Tacoma Community College
Tacoma, Washington , USA
I just picked another copy of "A Potter's Book". This one a Third
American printing from 1948 (First printing from 1946, and the second in
'48 also.) in excellent condition.
I might be persuaded to part with it. If anyone is interested in
owning a copy contact me off the list.
______________________________________________________________________________
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.
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Snail Scott on fri 31 jan 03
At 12:36 PM 1/30/03 -0800, you wrote:
>Also I have not heard of Black Cobalt
>Oxide - is that a typo?
As far as I know, all cobalt oxide is black.
(Cobalt carbonate can be pink, or blue if
calcined.) These are the unfired colors,
though. They're all blue when fired. Cobalt
oxide is a stronger colorant, though, (look
at the molecular formula) and I've always
wondered if perhaps it's not really black,
but an intensely dark blue. Any thoughts?
-Snail
Russel Fouts on sat 1 feb 03
Speaking of naturally occuring cobalt, I think it's in Cobalt Ontario
where you can pick up impure cobalt pebbles off the ground. There was a
clayarter several years ago who reported this, had a whole bucketful.
Apparently ,it's contaminated with arsenic but that can be got rid of by
calcining and venting your kiln.
Could be very interesting.
Russel
--
Russel Fouts
Mes Potes & Mes Pots
Brussels, Belgium
Tel: +32 2 223 02 75
Mobile: +32 476 55 38 75
Http://www.mypots.com
Home of "The Potters Portal"
Over 1800 Pottery Links!
Updated frequently
"Is the Hokey Pokey really what it's all about?"
Russel Fouts on mon 3 feb 03
Francoise
>> Russel, I visited Cobalt, Ont. a few years back and found it a to be a depressing place, almost a ghost town, with just a few dingy souvenir shops selling assorted junk and minerals. Of course, I hunted around the wastelands for cobalt-bearing rocks, but with no luck. I asked some locals if there were any around, but they shrugged and said they hadn't a clue. Maybe I just didn't know what to look for. <<
I think the person who wrote the original post got in touch with a local
geologist who pointed them to the sources.
Russel
--
Russel Fouts
Mes Potes & Mes Pots
Brussels, Belgium
Tel: +32 2 223 02 75
Mobile: +32 476 55 38 75
Http://www.mypots.com
Home of "The Potters Portal"
Over 1800 Pottery Links!
Updated frequently
"Is the Hokey Pokey really what it's all about?"
Tom Buck on mon 3 feb 03
Snail, Linda, Lili, others:
The following was prepared for sgraffito, the newsletter of Hamilton &
Region Potters Guild:
by Tom Buck, chemical engineer
The Cobalt materials we buy have names different from their "real"
chemical names and formula. The Carbonate is not pure carbonate, it is a
mix of carbonate and hydroxide; and the Oxide may well be a mix of two
oxides.
To make Cobalt Carbonate Basic, producers combine soda ash and cobalt
(II) acetate in water solution. The solid that forms is recovered from the
liquid by filtration, dried and shipped to market. It is described as being
red violet crystals that are insoluble in cold water but will decompose in
hot water. When it is heated in a glaze, the Carbonate Basic changes to
CoO, ie, Cobalt (II) Oxide.
If your Carbonate is pale lavender that probably means it also
contains some colour-inert whitish powder (clay? feldspar? flint?). Ask
your supplier for an analysis, or, ask for an answer to this question: how
much of the element, Cobalt, is present. It likely will contain 50% or less
of elemental Cobalt instead of the theoretical 55% (ie, 100% pure carbonate
basic).
Cobalt forms two oxides: Cobalt (II) Oxide, CoO; and Cobalt (III)
Oxide, Co2O3. But the producers likely ship a mixture of both.
Cobalt (II) Oxide is made by "roasting" the Carbonate Basic compound,
and the result is a greyish powder that is quite dense (6.4 g/mL) with very
high melting point (1935 oC). This insoluble material is supplied in two
grades, technical and ceramic. It has several uses aside from pottery.
The other oxide, Co2O3, is a steel-grey or black powder, density
4.8 g/mL, insoluble in water. It changes to CoO at 895 oC. It is made from
other cobalt compounds by heating them at low temperature with excess air.
It is used chiefly as a pigment and an enamel/glaze colourant.
Some makers of Cobalt Oxide ship a material of vague composition, it
is between Cobalt (II) and Cobalt (III) Oxide, and sometimes a formula of
Co3O4 is cited, which is CoO.Co2O3 in equal molar amounts. This oxide mix
arises when cobalt compounds are heated (as above) to form CoO or Co2O3. So
commercial Cobalt Oxide generally contains significant amounts of
CoO.Co2O3; the result is a steel grey to black powder with a density of 6.1
g/mL.
Since neither the Carbonate nor Oxide is pure, the substitution factor
--Oxide to Carbonate-- may range from 1.3 to 1.4 for a similar blue tone.
Hence, we need a test or two to determine which value is right for our
powders. Each of us will choose a preferred hue, obtained by a few tests
using stock on hand, then we use that factor until new cobalt stock
arrives. Then the tweaking process begins again.
Copyright (C) 2000 by Tom Buck, All rights reserved. If you wish to make a
copy of this material for other than personal use, please ask for
permission (usually granted).
til later. Peace. Tom B.
Tom Buck ) -- primary address.
"alias" or secondary address.
tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street, Hamilton ON L8T 3E1 Canada
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