Natural pearlescence

The simultaneous reflection of light from many parallel layers produces the characteristic pearly luster, the hril-liance of which depends on the uniformity and parallelism of the crystals. Natural pearlescent pigments are composed primarily of guanine crystals derived from fish scales. They are expensive but nontoxic. The synthetic pearlescents are based on crystallized lead or bismuth compounds or platelets of mica coated with a dye or pigment. (Bailey s industrial oil and fat products. Shahidi F, Bailey AE (eds). Wiley, New York, 2005)... 

The pearlescent effect in natural pearls arises because of the interaction of incident light with alternating layers of high refractive index (CaCOj) and low refractive index (protein), reflected and diffracted light from which leads to the observed iridescent colours. 

Synthetic or natural pigments used to achieve lustrous, brilliant, or iridescent color effects by interference on thin optical films are called nacreous or pearlescent pigments [5.190]—[5.194]. They were originally used to simulate the appearance of... 

Nacreous Pigments Nacreous, i.e.. pearlescent pigments are used for creating special decorative effects typical of natural pearls. Nacreous pigments are fine, thin, plate-like transparent particles having a high refractive index. Because of these physical characteristics, when dispersed in a transparent film, they produce a silky appearance. 

The most common class of pearlescent pigments today is based on thin platelets of mica (see Fig. 15.5). Mica itself is a natural mineral and belongs to the sheet layer silicates. Nacreous pigments are usually based on natural, transparent muscovite and only in some cases on synthetic phlogopite. Muscovite occurs worldwide, but only few deposits are suitable for pigment production. Mica is biologically inert and approved for use as a filler and colorant. 

Pearlescent pigments can also be used in plastic formulations to produce mar-bleized and frosted effects. Marble effects using pearlescent pigments show the typical crystalline lattice structure of natural marble and make the effect appear more real in plastics. The effect known as the frost effect is easily produced while using the pearlescent pigments at very low loading levels (0.2%) in the transparent resin system. 

The use of bismuth as a beauty care product dates back to antiquity and is still used in common cosmetic products. Bismuth oxychloride is used to impart a pearlescent effect to lipstick, nail varnish, eye shadow, and makeup powder. The resulting brilliance and luster surpasses that of a natural product, guanine, which is extracted from fish scales and is more costly. 

Although pearlescent pigments encompass the natural pearl essence derived from the fish and also the various crystal forms of bismuth oxychloride, it is the coatings of titanium dioxide and iron oxide on mica that have gained the most acceptance and are the most commercially successful. It is the coatings of titanium dioxide on mica and their derivatives that are the subjects of this study. 

Lanolin and mineral oil (or their substitutes) are often added to shampoos to replace the natural oils in the scalp, thus preventing it from drying out and scaling. The presence of oil additives and stabilizers sometimes gives the shampoo a pearlescent appearance. These ingredients also make the shampoo less foamy, a quality that is popular in European countries. 

The original pearlescent colorant was natural pearl essence (natural fish scales). The material is too fragile for most plastics processing, but it has been used in cellulose acetate eyeglass frames. Synthetic pigments include basic lead carbonate, lead... 

Customers are looking for products with a more natural look, according to Hanna. Trend-setting applications now include white stone and earthenware (terracotta) effects, created for indoor and outdoor products, as well as wooden chairs and tables. Building on its experience with fibres, beads, pearlescent, and fluorescent effects, the company has developed a range of natural effects. 

Natural pearl essence is very expensive but shows some advantages over synthetic pearlescent 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 settling in liquid formulations. It is almost exclusively used in expensive cosmetic applications. 

The dominant class of pearlescent pigments is based on platelets of natural mica coated with thin films of transparent metal oxides The mica substrate acts as... 

Instead of mica, SiOj flakes can be used as a substrate for pearlescent pigments. The SiOj flakes are produced by a web-coating process. Synthetic SiOj flakes offer three advantages over the use of natural mica (1) the thickness of the SiOj substrate can be controlled in the preparation so that at the end a pigment with a true... 

Pearlescent por- le-s nt adj (1936) An appearance resembling that of natural pearls or mother-of-pearl it results from the specular reflectance of alternating thin layers of differing refractive index similar to nacreous, interference color the pigment particles are transparent, thin platelets of high refractive index which partially reflect and partially transmit incident light simultaneous reflection from many layers of oriented platelets creates a sense of depth that is characteristic of nacreous luster. Syn Nacreous. See Interference Color. (Bailey s industrial oil and fat products. Shahidi F,... 

Chem. Descrip. Water, propylene glycol, linoleamidopropyl PG-dimonium chloride phosphate, PEG-5 dihydroxypropyl linoleaminium chloride, glycol stearate, sodium laureth sulfate, hexylene glycol Ionic Nature Cationic Uses Conditioner, pearlescent for hair care Features Provides wet comb out... 

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