search  current discussion  categories  materials - cobalt 

cobalt content

updated sat 6 mar 99


Gavin Stairs on thu 12 mar 98

This relates to a thread long past: the relative Cobalt content in cobalts
available for ceramic use. Some people, including me, posted information
that seemed to indicate that cobalt silicate was probably not cost
effective, even though it would be more consistent as a glaze ingedient.
Well, I just asked PSH about the cobalt content of their materials, and
this is what I found out:

The PSH web site lists the following materials.
The prices are in Canadian dollars.
100g 500g 1kg
6.29.230 Cobalt carbonate 13.75 54.00 96.00
6.29.231 Cobalt silicate 9.95 39.90 72.00
6.29.232 Cobalt oxide 19.50 80.00 143.00

And Jon Walls of PSH replied to my query with:

"The CoO contents of the cobalt compounds we offer are: carbonate (60.0);
silicate (61.9) and oxide (90.3). As you can see, cobalt silicate and
carbonate are almost interchangeable; raising either by 50% makes them
roughly equivalent to the oxide. Of the three, cobalt silicate will be the
least likely to cause dark speckling which can arise from dispersing
difficulties associated with the other two."

This means that the cost of cobalt in the various forms, calculated from
the 1kg quantities, is:
C$/kg(CoO) % of CoO
Cobalt carbonate 96/0.6 = 160.00 101.0
Cobalt silicate 72/0.619 = 116.32 73.5
Cobalt oxide 143/0.903 = 158.36 100.0

This indicates that the cost of the silicate is not always higher than the
other forms. Also note that the cost of the oxide and carbonate are about
the same.

So, from PSH as at 98.03.10, for general colorant use, 6.29.231 Cobalt
silicate is the best buy from any standpoint. For special purposes
(specking, etc.) the oxide may be better than the carbonate.

1. I have NOT confirmed these numbers by experiment.
2. Please note that material from other suppliers may vary. I suggest you
ask your own questions.


Tom Buck on fri 5 mar 99

I would question the manufacturer's value for cobalt as oxide. If
he is citing the black powder as CoO (or even as Co2O3), and one assumes
98% purity of the resultant powder, then the best one could expect for
Cobalt content -- as the element not as oxide -- is: 80% Cobalt metal if
the material is CoO, and 72.5% Cobalt metal if it is Co2O3.
Again, assuming 98% purity, the Carbonate Basic would have a
Cobalt metal content of 54%.
So to my view, there is something missing in the data the
manufacturer supplied you, or a mis-communication of some sort.
But to be fair, it really matters little what the "real" numbers
are. What counts is the colour you get on your pots, and if your ratio
works for you, well and good.
Yet, for someone starting to emulate a glaze mix from elsewhere,
having a good conversion factor for Cobalt compounds really would save
some wheel-spinning. And I suggest 2 Carbonate to 1 Oxide is not a good
start. More likely it would be 100 grams Oxide equals 130 grams Carbonate
Basic, or at most 140 grams Carbonate Basic. Or 77 grams Oxide equals 100
(plus) grams of Carbonate Basic.
Til later. Stay cool. Tom.

Tom Buck ) tel: 905-389-2339
& snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
(westend Lake Ontario, province of Ontario, Canada).