Substrate-Free Pearl Luster Pigments

Substrate-Free Pearl Luster Pigments Natural Pearl Essence 

Natural pearl essence is isolated as a silky lustrous suspension from fish scales. The organic pigment particles in the suspension are platelet-shaped with a very high aspect ratio (0.05 pm x 1-10 pm x 20-50 pm), and consist of 75-97% guanine and 3-25% hypoxanthine (natural fish silver) [5.122, 5.123, 5.128, 5.130]. 

Natural pearl essence is very expensive but shows some advantages over synthetic pearl luster pigments. For example, it shows a high but soft luster (no = 1.79 (parallel) to 1.91 (perpendicular)). It is not brittle and has a relatively low density of 1.6 g cm which reduces setthng in liquid formulations. It is almost exclusively used in expensive cosmetic applications. 

The first commercially successful synthetic pearl luster pigments were hexagonal lead salt crystals, especially basic lead carbonate Pb(OH)2 2 PbCOs. Basic lead carbonate is precipitated from aqueous lead acetate with carbon dioxide under carefully 

The resulting platelets are less than 0.05 pm thick and show hexagonal dimensions of about 20 pm, yielding an aspect ratio of 200. Because of their high refractive index of 2.0 and their even surface, they exhibit a very strong luster. If the thickness of the platelets is increased by slightly modified reaction conditions, interference colors can be obtained [5.122, 5.123, 5.128, 5.130]. 

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