Organic pigments dispersion mechanisms

The thickness of the platelets can be adjusted by controlling the reaction conditions to produce interference colors. The pigment crystals are mechanically sensitive and show a fast sedimentation behavior because of the high density (6.4gcm 3). Agglomeration tendency and occupational health (toxicity) risks are the reason why Pb(OH)2 2PbC03 is not produced in powder form, but is flushed from the aqueous phase into suitable organic solvents or resins and handled as stabilized dispersions. Today, the application of basic lead carbonate is limited to artificial pearls, buttons, and bijouterie. 

The melanin of sepia is found in the ink sac of cuttlefish. Aristotle in his book Historia Animalia mentioned that instead of intestines molluscs have an organ known as the mytin where a black substance is found which is especially abundant in cutdefish they put forth this black substance when frightened, particularly the cuttlefish . The ink has considerable staining power, and is alkaline and odorless. When fresh it disperses readily in water and is partly soluble in alkali, but insoluble in acid. This biological function of melanin appears to be defensive but the mechanism is uncertain (270). However, like other pigments, melanin can be utilized for camouflage purposes in insects and fishes. 

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