cobalt pigment

Noticed that (MC8) developed som e needle-like crystals on its
surface; possibly Na2CO3? It was drier and more friable, presumably
because of the loss of NaOH.  Weight 2.3 g.

Added 5.2 g of NaOH flakes in an inox can. Heated on electric stove
for 0 min at 327 C. Result was a viscous molten black mass (MC15).

Let it cool then added some water. Heated it again to cmplete
dissolution minus a few grains. Result was a blue-black liquid (MC16).

Filtered (MC16) with 28 µm paper:

* Liquid (MC17) clear royal blue.

* Solid (MC18) olive black ppt.

The inox cup was partly corroded with brown "rust".

(MC9) Turned blacker and more opaque with time.  Reheating to boiling point
restored transpacency and color almost completely.

(MC17) turned blackish even before the filtering was over.

Precipitate (MC14) was pressed between napkins. Some were contaminated
with NaOH that left blue stains on ppt. Microsc. still showed mostly
the rod-shaped crystals, slightly pink or yellow.

(MC18) was brown after washing. Perhaps contamination from inox cup?
Microsc. showed mixture of fine dark particles (navy blue or black)
and larger yellow-brown flakes.

(MC17) After ~1 h became cloudy with ppt of unclear color.

----------------------------------------------------------------------