cobalt pigment

Concentrated (MC9) by boiling.

After ~24 h (MC17) was a bluish black opaque suspension with an off-white ppt
at the bottom.

Filtered again (MC17) throughg 28 µm paper. 

* Liquid (MC19) clear very light blue.

* Solid (MC20) black or dark ppt.

Shaking (MC9) apparently increases the black suspended ppt.
Perhaps oxidation is the key?

Put ~3 mm of (MC9) in a test tube.  Added 1.5 mL lactic acid 85%, 1.0 mL H2O.
Bubbling. Blue color disappeared, white fluffy ppt formed.

In a test tube (MC9d) added ~1cm (MC9) then ~2mL H2O2 30%. The H2O2
decomposed violently in contact with solution. However, by stirring
after each drop, the entire liquid was discolored and cloudy, with a
suspended black ppt.

Then added a little ascorbic acid, not enough to neutralize the
NaOH.  Solution became clear blue again with no trace of black ppt.


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