Anthony G Allison on tue 27 jan 98
If any of you have an occasion to travel though Canada, a stop at Cobalt
Ontario would be worth the trip. The whole town is sitting on cobalt rock.
We picked up 100 lbs 5 gallon pail full a couple of years ago. This lifetime
supply was kindly given to us by the queens geologist there. He told us to
roast the ore before using it as it contains some arsenic. They mined silver
there so there is probably some silver also. This ore produces a blue of
tremendous variety and softness.
If you obtain some (the geologist said just place an ad in the local paper),
Dont make the same mistake I made of trying to roast the ore in your kiln in
a bisqued bowl. (My kiln floor is covered with a 1/2 inch layer of cobalt
that ate through the bowl when it melted.) When I need cobalt I go out to
the kiln with a chisel. #@$%$# !@!!!
With the high price of cobalt, thought this tip may be of real use to
someone who likes character in their pots, and also like to save $$$
Lisa P Skeen on wed 28 jan 98
Tony: A couple of questions come to mind.
How do you make the chunks of cobalt useable? Are you grinding it down
w/ a mortar & pestle or do you have a ball mill?
Second: Since the cobalt ate through your bisqueware, what would you
suggest for cooking the cobalt?
Lisa Skeen, Living Tree Pottery and Soaps
On Tue, 27 Jan 1998 07:56:12 EST Anthony G Allison
>If any of you have an occasion to travel though Canada, a stop at
>Cobalt Ontario would be worth the trip. The whole town is sitting on
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Richard Mahaffey on fri 31 jan 03
There IS black copper oxide (CuO) and it is pretty black. That is the
commonly used. There also is red copper oxide (Cu20) which is a lovely
I have seen "Black" copper oxide as
well even though it rarely produces a balck color in a glaze.
Seems we are in agreement. There is black copper oxide. The black in
the name refers to the color in the powder form,
just like the black in black cobalt oxide refers to the color in powder
Neither one produces a black in a glaze. You can make a very dark blue
with enough cobalt, but it is not optically black.
I did not decide to name the cobalt oxide black, that happend long
ago. If it is god enough for Bernard Leach it is good enough for me.
Who seems to have nothing better to do on a Friday night.
Tracey Duivestein on mon 25 jun 07
What a relief to have Clayart back again. As a "digester", all I could =
do was hope & pray. A huge thanks to all those boffs who got it up & =
Please can someone give me the substitution ratio for cobalt oxide & =
cobalt carbonate. I am planning to throw some salad bowls & platters =
using 2 different coloured clays and only have cobalt oxide. In the =
archives Vince Pitelka gives a handy clay colouring thread, but he uses =
Is there a ratio between plain & coloured clay to get the best marbled =
effect. Previously, I used a chunk of terracotta with a bigger chunk of =
buff, never giving ratio a thought. I have a quantity of pale cream =
clay that isn't suitable for raku ( I learned the hard way), so have to =
use it somehow.
Durban, South Africa - in the middle of a very warm spell in what's =
supposed to be "winter". I believe a cold front is due on Wed - we will =
Maurice Weitman on mon 25 jun 07
I hope your weather smoothes out for you.
>Please can someone give me the substitution ratio for cobalt oxide &
>cobalt carbonate. I am planning to throw some salad bowls &
>platters using 2 different coloured clays and only have cobalt
>oxide. In the archives Vince Pitelka gives a handy clay colouring
>thread, but he uses cobalt carbonate.
Since you're familiar with clayart's archives, you'd find several
hundred mentions of this.
Here's one (I believe from Denis "Smart " Caraty) that I paraphrased
and believe to be correct and easy to use:
100 g of Cobalt oxide (Co3O4) gives about 97 g of CoO (Cobalt basic oxide)
100 g of Cobalt carbonate (CoCO3) gives 63 g of CoO (Cobalt basic oxide)
Cobalt basic oxide is what you need in your glaze.
So you can substitute 1 part of Cobalt oxide with 1.5 parts of Cobalt carbonate
and if you reverse the calculation,
You can substitute 1 part of Cobalt carbonate by 2/3 of a part of Cobalt oxide.
Perhaps someone else can help you with your clay percentage query.
Maurice, in seasonal Fairfax, California, where I'm close to having
my new(er) pug mill working, and where I'm mostly happy clayart's
back, and from where, if I have the time (and stomach), I'll write
about my discussions with folks at ACerS over the past two weeks, and
with Mel over the past three years, about what I believe to have
happened, what should have happened, and why things are not likely to
change any time soon.
Oh... and remind me to tell you about my daughter who's just moved to
Florida from Brooklyn (although she's still a Yankees fan, much to my
chagrin) and is quite ready to pop her first kid, my second
granddaughter. I'm ready, too. She wasn't ready to hear my
mmmmmmwwwwwwaaaaahhhhhhhhhaaaaaahhhhhhhaaaaaaas as my Giants wupped
her overpaid Yanquis yesterday (and the day before). Take THAT,
Dave Finkelnburg on tue 26 jun 07
The short answer to your question is: grams cobalt
carbonate times 0.63 = grams cobalt oxide.
Cobalt oxide is CoO (chemical formula. Since
cobalt weighs 59 grams/mole, and oxygen weighs 16, a
mole of the oxide is 59 + 16 = 75 grams.
Cobalt carbonate is CoCO3. Carbon weighs 12
grams/mole, so a mole of the carbonate is
59+12+(3 x 16) = 119 grams.
The key here is the mole. No, this one isn't a
furry rodent! :-) It's a specific number of atoms,
and the calculations show that 75 grams of cobalt
oxide have the same number of atoms of the colorant
cobalt as 119 grams of the carbonate.
If your recipe calls for 1 gram of the carbonate,
multiply that by (75/119) or 0.63 to get the grams of
cobalt oxide that will have the same amount of cobalt.
By the way, the appearance will not necessarily be
identical. The particle size of the carbonate appears
to me to be generally finer.
From: Tracey Duivestein
Please can someone give me the substitution ratio for
cobalt oxide & cobalt carbonate.
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