Joseph Herbert on thu 14 feb 02
Cobalt oxide (CoO) has a molecular weight of 74.9
Cobalt carbonate (CoCO3) has a molecular weight of 118.95
To get the same number of cobalt atoms using the carbonate, 1.6 times as
much carbonate should be used as the oxide.
The "twice as much" rule may have something to do with color perception
ability or the fact that the oxide tends to be in grains while the carbonate
is a more easily suspended fine powder. The strongly colored glaze areas
resulting from the use of the clumping oxide may make a greater perceptual
contribution to the blue than do the more evenly distributed but smaller
colored areas resulting from the carbonate. If cobalt didn't cost so much,
it wouldn't matter but it does and the additional 32 grams of carbonate is
an "excess" 27% of a mole of the material.
It may be necessary to use the greater amount to get the color your eye
wants, but on an atom-for-atom basis, the smaller amount should be correct.
Joseph Herbert
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