17 ноября, 2015 
Pokraskin The purification and refinement operations can be batch or continuous. The raw blue is crushed and ground, slurried in warm water, then filtered and washed to remove the sulfoxides. Reslurrying and wet grinding release the sulfurous impurities and reduce the ultramarine particle size, often to 0.1-10.0 gm. The impurities are floated off by boiling or cold froth flotation, analogous to techniques used in the mining industry.
The liquor is then separated into discrete particle size fractions by gravity or centrifugal separation; flocculation and filtration reclaim residual fine particles. The separated fractions are dried and disintegrated to give pigment grades differentiated by particle size. These are blended to sales-grade standard, adjusting hue, brightness and strength to achieve specified color tolerance.
Violet ultramarine can be prepared by heating a mid-range blue grade with ammonium chloride at ca. 240 °C in the presence of air. Treating the violet with hydrogen chloride gas at 140 °C gives the pink derivative.
A good ultramarine pigment would meet the following specification:
±5% max
1 CIELAB unit max 0.05% max 1.0% max 0.1% max 1.0% max traces
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