Pearl

Pearls are growths that form inside the shells of mollusks, usually in response to the presence of a parasite or other irritant. They are composed of layers of nacre that the animal secretes over the foreign body. Pearls tend to be the same color as the nacre inside the shell. Sometimes pearls are loose, forming in the mantle cavity, and sometimes they become attached to the inside of the shell. These latter pearls are called blisters and may contain rotten organic matter or a smaller, loose pearl. 

Natural or oriental pearls are produced naturally by bivalves, such as oysters and clams, and by a few gastropods, such as abalone. Cultured pearls are induced by the introduction of foreign objects into the mantle cavity. Modem cultured pearls are usually seeded with a sphere made from the shell of Mississippi River mussels (family Unionidae). The culturing process involves prying open the shell and inserting both the seed or nucleus that will become the core of the new pearl, and a piece of donated mande tissue from another oyster. 

Mabe pearls are based on a hemispherical nucleus that is inserted through a hole drilled in the outside of the oyster s shell and glued into place. The animal inside will secrete nacre over this round knob which, when harvested, will yield a large pearl that is flat on one side. Mabes and other blister pearls can only be harvested by killing the oyster, since they must be cut out of the shell. 

The longer a cultured pearl stays in the oyster, the more layers of nacre there will be. If a pearl is harvested too soon after the nucleus is deposited, the layers of lustrous nacre may be so thin that they wear away when the pearl is used in jewelry. 

Cultured freshwater pearls are produced by placing a tiny piece of mande tissue inside the shell. Some bivalves can take many of these tissue seeds at the same time, unlike marine oysters, which will usually only make one or two pearls at a time. 

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In mass polymerization bulk monomer is converted to polymers. In solution polymerization the reaction is completed in the presence of a solvent. In suspension, dispersed mass, pearl or granular polymerization the monomer, containing dissolved initiator, is polymerized while dispersed in the form of fine droplets in a second non-reactive liquid (usually water). In emulsion polymerization an aqueous emulsion of the monomer in the presence of a water-soluble initiator Is converted to a polymer latex (colloidal dispersion of polymer in water). 

Several studies have demonstrated the successful incoriDoration of [60]fullerene into polymeric stmctures by following two general concepts (i) in-chain addition, so called pearl necklace type polymers or (ii) on-chain addition pendant polymers. Pendant copolymers emerge predominantly from the controlled mono- and multiple functionalization of the fullerene core with different amine-, azide-, ethylene propylene terjDolymer, polystyrene, poly(oxyethylene) and poly(oxypropylene) precursors [63,64,65,66,62 and 66]. On the other hand, (-CggPd-) polymers of the pearl necklace type were fonned via the periodic linkage of [60]fullerene and Pd monomer units after their initial reaction with thep-xy y ene diradical [69,70 and 71]. 

The irradiation darkening to produce black pearls is merely a charring of the organic conchiolin. 

When a eutectoid steel is slowly cooled from the austenite range, the ferrite and cementite form in alternate layers of microscopic thickness. Under the microscope at low magnification, the diffraction effects from this mixture of ferrite and cementite give an appearance similar to that of a pearl, hence the material is called peadite. 

I. A. Pearl, The Chemistry ofEignon, Marcel Dekker, Inc., New York, 1967. 

Suspension Polymerization. At very low levels of stabilizer, eg, 0.1 wt %, the polymer does not form a creamy dispersion that stays indefinitely suspended in the aqueous phase but forms small beads that setde and may be easily separated by filtration (qv) (69). This suspension or pearl polymerization process has been used to prepare polymers for adhesive and coating appHcations and for conversion to poly(vinyl alcohol). Products in bead form are available from several commercial suppHers of PVAc resins. Suspension polymerizations are carried out with monomer-soluble initiators predominantly, with low levels of stabilizers. Suspension copolymerization processes for the production of vinyl acetate—ethylene bead products have been described and the properties of the copolymers determined (70). Continuous tubular polymerization of vinyl acetate in suspension (71,72) yields stable dispersions of beads with narrow particle size distributions at high yields. 

Guanine (Pearl Essence). Guanine (Cl Natural White 1, Cl No. 75170), is the crystalline material obtained from fish scales and consists principally of the two putines, guanine [73-40-5] (42) and hypoxanthine [68-94-0] (43). The guanine content of the colorant varies from 75% to 97%, whereas the hypoxanthine content ranges from 3% to 25%, depending on the particular fish and tissue from which the crystals ate derived. 

Bismuth oxychloride [7787-59-9]—Cl Pigment White 14, Cl No. 77163. A synthetically prepared white or nearly white amorphous or finely crystalline, odorless powder consisting principally of BiOCl. Bismuth oxychloride is synthetic pearl essence. It is used in Upstick, nail poHsh, eye makeup, and other cosmetics to produce a lustrous, pearly effect. 

CA Orengo, EMC Pearl, JE Bray, AE Todd, AC Martin, L Lo Conte, JM Thornton. The GATH database provides insights into protein stmcture/function relationship. Nucleic Acids Res 27 275-279, 1999. 

Chemical Designations - Synonyms Basic Bismuth Chloride Bismuth Chloride Oxide Bismuth Subchloride Bismuthyl Chloride Pearl White Chemical Formula BiOCl. 

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