MATERIAL MAN - PART SEVEN: COBALT

FRIDAY, 9 MARCH 2012

COBALT GIVES ME THE BLUES, 

THE LILACS,  THE MAUVES AND SOMETIMES THE PINKS!

I DON'T OFTEN USE COBALT IN MY OWN WORK THESE DAYS, BUT MANY YEARS AGO I REALLY ENJOYED MIXING 2% COBALT CARBONATE, 2% COPPER CARBONATE AND 5% TIN OXIDE. IT WAS MIXED WITH A LITTLE GUM ARABIC OR CMC, AND PAINTED ON A SATIN-SURFACED WHITE GLAZE THAT WAS FIRED IN REDUCTION AT CONE 9 - 10.  THE RESULT WAS A DARK LUSTROUS BLUE, SURROUNDED BY A HALO OF COPPER RED THAT HAD FUMED ITS WAY INTO THE WHITE GLAZE. I LOVE COLOR MIXES THAT DEVELOP HALOS AROUND THE MAIN COLORANT. 

COBALT  COMPOUNDS ARE THE MOST POWERFUL OF THE COLORING OXIDES IN THEIR COLORING ABILITY. BETWEEN1% AND 3% IS NORMALLY STRONG ENOUGH FOR MOST USES. THEY ARE ALSO STRONG FLUXES. IN GLAZES DOMINATED BY COLOR-AFFECTING FLUXES, THE FOLLOWING VARIATIONS MAY BE EXPECTED:  IN LEAD GLAZES, PALE TO DARK INKY BLUE-BLACK; IN BARIUM, STRONTIUM AND ALKALINE  EARTH GLAZES, BRILLIANT ULTRAMARINE; IN HIGH MAGNESIUM GLAZES, PINK LILAC AND PURPLE BLUE; IN ZINC GLAZES, SOFT GREY BLUES; AND IN GLAZES CONTAINING FLUORSPAR, CERULEAN BLUE MAY BE ACHIEVED. THE CARBONATE  FORM OF COBALT IS MORE FINELY GROUND THAN THE OXIDE FORM.  COBALT COMPOUNDS ARE USUALLY MIXED WITH OTHER MODIFYING COLORANTS TO ELIMINATE THE HARSHNESS OF THE PURIFIED MATERIALS.  INDUSTRIALLY PREPARED COLORANTS USING COBALT ARE OFTEN CALCINED AND GROUND WITH OTHER MATERIALS TO IMPROVE COLOR AND ELIMINATE SPECKING. JAPANESE BLUE PIGMENT CALLED GOSU IS NORMALLY A MIXTURE OF COBALT I, MANGANESE 3 AND IRON 2,  USED IN DIFFERENT STRENGTHS OF SOLUTION FOR A VARIETY OF TONES. COBALT USED OVER 7% IN HIGH MAGNESIUM WILL OFTEN TURN TO A SUGARY PINK.

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MY FAVORITE DRAWING TOOL

 FOR SLIPS AND GLAZES

STAINLESS SLIP/GLAZE TRAILERS

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