- - - -Cited by Gerhard Pfaff <Special Effect Pigments> Dr. Gerhard Pfaff

The luster of valuable pearls even fascinated people in the ancient world, because it differs from the normal luster of smooth surfaces with its nuances between matt and mirror luster. Pearl luster appears three-dimensional and seems to come from a depth within the object. A 3000- year-old Chinese document contains proof that humans attempted to imitate the tremendous color luster of pearls. It describes the attempts made to produce pearls with a special luster by mixing various materials.

Since the 11 century, experienced glass technicians of Venice produced man-made pearls with such a quality that the government felt it necessary to prohibit this. The secret of this production disappeared in the course of time with its producers [2] First attempts to imitate pearls in France, coating small gypsum pearls with fish scale paste were unsuccessful because the body heat of the carrier tended to melt the glue fixing the scales.

The history of transparent luster pigments began 1656 in Paris when Jaquin isolated the silvery substance of the inside of fish scales and developed a suspension with silver lusterl3. This first pearl luster suspension with its brilliant luster was called "Essence d'Orient”It contained the same substance, which was later called natural fish silver. In the 17h century, buttons made of mother-of-pearl became popular and led to an upswing in the button industry in various European countries.

The development of polymethyl methacrylate and unsaturated polyester led to a new material basis for button manufacturing. Since buttons based on these polymers should further demonstrate the luster and the colored character of nacre, the search for synthetic materials in form of pearl luster pigments started and herewith the replacement of natural fish silver and mother of pearl, in this application and other branches. The most valuable of all newly developed pearl luster pigments proved to be basic lead carbonate. Bismuth oxychloride, which could be manufactured in form of thin platelets grew to be the second most important synthetic pearl luster pigment.

Around 1960 new pigment generation on the basis of metal oxide coated mica platelets was introduced to the market. The first of these pearl luster pigments to replace basic lead carbonate from its application areas were titanium dioxide mica pigment. Today there are a multitude of variations of such pigments for many decorative and technical applications on the market. The use of oxide such as iron oxides, chromium(II) oxide or mixed oxides instead of titanium dioxide permits a steady growing application of artificial pearl luster effects.

The development of new effect pigments has been continued in the last 10 to 15 years in an accelerated manner. It was decisive for this development that the possibilities for the manufacture of transparent synthetic platelets were created. These new substrate platelets are suitable for the coating with metal oxide layers in addition to mica. Platelets of silicon dioxide (silica flakes), aluminum oxide (alumina flakes), or borosilicate (borosilicate or glass flakes) belong to these new substrate materials. Additionally, synthetic mica (fluorophlogopite) is meanwhile also used instead of natural mica (muscovite) for the production of new effect pigments.

Natural mica mainly is the basis of the development of various functional effect pigments in the last years. Platelet-like electrically conductive pigments, pigments with special UV, VIS and IR properties as well as pigments suitable for the laser marking of polymers belong to this new class of materials.

New developments in the range of decorative effect pigments are multilayer pigments with Fabry-Perot structures, pigments based on liquid crystal polymers as well as pigments with structured surfaces. The history of effect pigments based on metal platelets is described in detail in the monograph “Metallic Effect Pigments”[4). Table 1.1 contains a historical overview on the development of special effect pigments.

References

[1] Kriger, A., ,,Perlen", Bibl. d. Unterhaltung und des Wissens, Union Deutsche Ver-

lagsgesellschaft, Stuttgart, 1919

[2] Simkiss, K., Wada, K,“Cultured Pearls - Commercialised Biomineralisation", Endeav-

our, 4 (1980) 32

[3] de Keghel, M., ,Falsche Perlen", Kunststoffe, 15 (1925) 216

[4] WijBling, P., Metallic Effect Pigments, Vincentz Network Hannover, 2006

[5] Pfund, A. H,“The Colors of Mother-of Pearl", J. Franklin Inst. (Philadelphia), 183

(1917) 453

[6] Atwood, F. C,, US 2,278,970

[7] Linton, H. R., US 3,087,828

[8] Linton, H. R., US 3,087,829

[9] Bolomey, R. A., Miller, H. A., Greenstein, L. M., US 3,123,490

[10] Bolomey, R. A., Quinn, C. A., Rieger, C. J., US 3,437,515

[11] Kohischitter, H, Getrost, H., Reich, w, Rossler, H., Horl, W., US 3,553,001