Crossword-Solution: DECOLOURISED 12 letters, 13 clues 🏆 scrabble score: 16

The best smalt in lumps appears black, yields a blue powder on grinding, becomes paler on further grinding, and may be almost decolourised by continued and excessive grinding.

Darkened as a rule by fire, factitious ultramarine becomes dingy blue, and at last white, when strongly ignited for a long time; and is, like the true variety, decolourised by ignition in an atmosphere of hydrogen gas.

Genuine ultramarine is always decolourised by acids; but it depends on the mode and nicety of its preparation whether it is decolourised without effervescence: that this is the case the author himself admits in his article on artificial ultramarine.

Seeing, therefore, that both sorts are decolourised by acids, and that both may or may not effervesce therewith, the acid test must be considered fallacious.

But being slightly soluble in water and decolourised by sulphuretted hydrogen, it would not, other considerations apart, be an acquisition.