cobalt_pigment

Trying to dissolve the cobalt pigment by first treating with concentrated NaOH.

Placed 1 g of pigment and 2 g of NaOH flakes in a beaker (previously frosted by NaOH) with enough water to dissolve the latter.  The suspension was dark lilac almost purple.  

Heated in BM for 10-20 minutes. Color became darker and grayer; a gray-black film formed on top.  Final color was blue-black.  Not much change was visible in microscope.

Diluted with water and filtered through 28 um paper.  Filtrate (MC1) was light purplish blue, cloudy.  Dilution made the ppt (MC4) lighter a bit: purplish gray.

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