C Pike on sat 11 oct 97
We have been having trouble with our shiny blue glaze -it is not
consistent-could it be the cobalt carbonate-it does seem a different color
each time we purchase it. We do fire in a gas kiln and there are variances
but the color is not right sometimes and it goes more matt. It is close but
not as rich as I would like it to be. Should I use a mason stain instead of
the Cobalt carbonate. Thanks Connie
The recipe is
Glaze name: EC Royal Blue Cone 10:
Recipe: Percent Batch
Potash Feldspar 43.59
Silica 28.21
Kaolin 10.26
Snow Whiting 17.95
Totals: 100.00 %
Also add:
Cobalt Carbonate 2.00 1 Lb 0oz
Unity Formula for EC Royal Blue:
0.191 K2O 0.446 Al2O3 4.175 SiO2
0.084 Na2O 9.4:1 Si:Al Ratio
0.725 CaO
Percentage Analysis:
69.65 % SiO2
12.64 % Al2O3
5.00 % K2O
1.44 % Na2O
11.30 % CaO
------------------------------------------------------------------------------
Bob & Connie Pike pikec@cadvision.com
1303 10th Ave SE High River,Alberta T1V 1L4 Canada (403-652-5255)
----------------------------------------------------------------------------
--
Diane Woloshyn on fri 26 feb 99
Recently bought Cobalt Carbonate from a supplier I seldom use. (Was in the
area). Have never used this before; have always used the oxide. I was very
surprised that the raw color was pale lavender. None of my reference books
list the color of the raw material. Have mixed some for firing, but now I am
wondering if this is the correct material, or did someone goof? Anyone?
Please reply to the list. I can't be the only relative beginner who doesn't
know. TIA
Diane Florida Bird Lady
Mike Gordon on sat 27 feb 99
Hi,
I use Copper carb all the time and it is always lavender, sometimes more
brilliant than other times. About $19.95 per half pound here in the S.F.
bay area, Mike
Alex Wilson on sat 27 feb 99
Dear Bird-Lady of Florida,
Relax, you'll be okie-dokie with the carbonate, and it is supposed to be that
colour.You'll also notice, in use, that there will be none of the darker
speckles often seen when the oxide is used. You might have to use a little
more of the carbonate than oxide to achieve
the same colour response and if firing very low temp., you'll need to calcine
the carbonate to avoid glaze blistering.
I hope this information proves useful to you.
Alex, The Scottish Potter
Nevada, Iowa
Mary Hess on sat 27 feb 99
Hi,
Colbalt Carbonate is pale lavender, and I use it just like colbalt oxide,
except I use a little more in recipes. The color is not quite as
intense at oxide, but it is cheaper. You can purchase both at
Clayworks Supplies in Baltimore. (410) 235-5998.
The Brinks on sat 27 feb 99
Hi Diane, that's it all right. What I have is almost pink, in fact. I
first used it for over-glaze brushwork (cone 7 on white glaze) and was
astonished at the vibrancy of the color...shocked is more like it. Hope
you like the results you get. Now I mostly use the oxide for brushwork
because you can see what you're doing. I use both in mixing glazes.
from Ann in CA, firing today, a cone 05 glaze firing...have sprinkled some
ground glass dust on some pieces as a test (daughter-in-law works w/stained
glass- gave me some dust from her wet-grinder) I suspect it will just act
as a flux in those spots.
At 08:42 AM 2/26/1999 EST, you wrote:
>----------------------------Original message----------------------------
>Recently bought Cobalt Carbonate from a supplier I seldom use. (Was in the
>area). Have never used this before; have always used the oxide. I was very
>surprised that the raw color was pale lavender. None of my reference books
>list the color of the raw material. Have mixed some for firing, but now I am
>wondering if this is the correct material, or did someone goof? Anyone?
>Please reply to the list. I can't be the only relative beginner who doesn't
>know. TIA
>
>Diane Florida Bird Lady
>
>
e-mail billann@impulse.net
Tom Buck on sat 27 feb 99
Since Diane asks for a reply to to list, asking about Cobalt Carbonate
versus Cobalt Oxide, I have some data for her and others.
Cobalt compounds of commerce aint chemically what their names
suggest; the Carbonate is not actually CoCO3 but a mix of the carbonate
and the hydroxide, so it should be called Cobalt II carbonate, basic, and
have this simple formula: 2CoCO3.3Co(OH)2.H2O molecular weight 534.6 (if I
did my sums correctly Co=58.93; C=12; O=16; H=1).
This material is produced from cobalt II acetate and sodium
carbonate, and the solid that forms is recovered from the liquid solution
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. As the compound is heated in a glaze it changes to cobalt oxide,
CoO. If your carbonate is pale lavender that probably means it has been
somewhat adulterated with perhaps some colour-inert whitish powder (clay?
feldspar? flint?). Ask for an analysis, ie, Cobalt (as element) content.
There are two oxides: cobalt III oxide, Co2O3; and Cobalt II
oxide, CoO. The CoO is made by heating 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 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, and which 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.
Unfortunately some oxide makers sell a mixed oxide material of
indefinite analysis, it may be somewhere between the two, although one
sometimes is told that the material has a formula of Co3O4.
If possible always ask your supplier for a percentage of Cobalt
(as element) in the oxide that is offered, so if you need a precise
molecular weight it can be calculated.
Happily that is seldom necessary since Cobalt is used at 2-3%
maximum in most glazes, so if the oxide is off by 10% whether you add 1.9
or 2.1% Cobalt oxide to the glaze recipe really won't make much
difference.
If your recipe calls for say 2% Cobalt oxide, then you need to use
2.7% of the Carbonate basic to equal that ... but of course one must
assume a mol wt of 240.8 for the oxide, and this will give an equivalent
value for the carbonate basic of 1.3 (one cannot be any more accurate
because one is not sure of the purity of the oxide.).
So, Diane, there you have it, and as you see your simple question
had a rather complex explanation but in the end a rather simple
conversion factor.
Good blues. BFN. Tom.
Tom Buck ) tel: 905-389-2339 & snailmail: 373 East
43rd St. Hamilton ON L8T 3E1 Canada (westend Lake Ontario, province of
Ontario, Canada).
On Fri, 26 Feb 1999, Diane Woloshyn wrote:
> ----------------------------Original message----------------------------
> Recently bought Cobalt Carbonate from a supplier I seldom use. (Was in the
> area). Have never used this before; have always used the oxide. I was very
> surprised that the raw color was pale lavender. None of my reference books
> list the color of the raw material. Have mixed some for firing, but now I am
> wondering if this is the correct material, or did someone goof? Anyone?
> Please reply to the list. I can't be the only relative beginner who doesn't
> know. TIA
>
> Diane Florida Bird Lady
>
Gwynneth Rixon on sun 5 sep 10
Hi=3D2C
I have some Cobalt Carbonate that has been in a jar for a while. It has now=
=3D
turned dark=3D2C from its original mauve colour. Will its properties hav=
e =3D
changed? Has its chemical formula changed?
Gwynneth
www.gwynnethrixonceramics.co.uk
=3D
William & Susan Schran User on sun 5 sep 10
On 9/5/10 11:58 AM, "Gwynneth Rixon" wrote:
> I have some Cobalt Carbonate that has been in a jar for a while. It has n=
ow
> turned dark, from its original mauve colour. Will its properties have
> changed? Has its chemical formula changed?
I don't know if cobalt is light sensitive, but doubt that might cause any
change. More than likely it may have absorbed a bit of moisture - jar
sitting in sunlit area might create greenhouse effect and this may have
darkened the surface. Give it a stir and see if interior has original color=
.
Doubt you'd notice any change in fired results.
Bill
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
Robert Harris on sun 5 sep 10
Fundamentally what you have will not have changed. There will still be
cobalt atoms in your powder, and that is what matters. The worst that
may have happened is that it has absorbed some moisture - this may
have changed it's molecular weight (and therefore in theory throw off
your measurements) but frankly it is unlikely to have altered it
enough that you will notice any difference whatsoever.
Robert
Larry Kruzan on mon 6 sep 10
I've seen this to without any change in effectiveness. It is possible it wa=
s
just a color change between batches.
Larry Kruzan
Lost Creek Pottery
www.lostcreekpottery.com
-----Original Message-----
From: Clayart [mailto:Clayart@LSV.CERAMICS.ORG] On Behalf Of Gwynneth Rixon
Sent: Sunday, September 05, 2010 10:58 AM
To: Clayart@LSV.CERAMICS.ORG
Subject: Cobalt Carbonate
Hi,
I have some Cobalt Carbonate that has been in a jar for a while. It has now
turned dark, from its original mauve colour. Will its properties have
changed? Has its chemical formula changed?
Gwynneth
www.gwynnethrixonceramics.co.uk
=3D
=3D=3D=3D=3D=3D=3D=3D
Email scanned by PC Tools - No viruses or spyware found.
(Email Guard: 7.0.0.18, Virus/Spyware Database: 6.15810)
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=3D=3D=3D=3D=3D=3D=3D
Gwynneth Rixon on wed 8 sep 10
Hi all=3D2C Thanks for the replies!
The main thing is that it works as before=3D2C but the even colour change t=
hr=3D
ough the jar is mystifying!
Gwynneth
www.gwynnethrixonceramics.co.uk
Date: Sun=3D2C 5 Sep 2010 19:49:25 +0100
Subject: Re: Cobalt Carbonate
From: original.mudslinger@googlemail.com
To: g.z.rixon@hotmail.com
No!
:-)
Steve
On 5 September 2010 16:58=3D2C Gwynneth Rixon wrote=
:
Hi=3D2C
I have some Cobalt Carbonate that has been in a jar for a while. It has now=
=3D
turned dark=3D2C from its original mauve colour. Will its properties hav=
e =3D
changed? Has its chemical formula changed?
Gwynneth
www.gwynnethrixonceramics.co.uk
=3D20
--=3D20
Steve
Bath
UK
www.mudslinger.me.uk
Growing old is inevitable=3D2C growing up is optional!
=3D
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