PEAEL ESSENCE 33 



The coating lacquers may be either aqueous or nonaqueous. The 

 ordinary water suspension preserved with ammonia or sahcyHc acid 

 and thickened with gelatin or glue may be applied to the bead, and 

 when this coat is dry a waterproof coat of collodion or other lacquer 

 is applied to protect it from moisture. Another aqueous lacquer con- 

 sists of a cupra-ammonium solution of cellulose (cotton), into which 

 the lustrous essence is mixed. This is applied to the bead and the 

 ammonia removed by evaporation and the copper by dilute hydro- 

 chloric acid, whereupon the coat is dried to finish the pearl. ^ 



The process now in general use employs a direct incorporation of 

 the lustrous guanin particles in collodion or cellulose nitrate or 

 celluloid solution in amyl acetate. This is applied to the bead in 

 from one to six or more coats, each of which is dried before the appli- 

 cation of the next. The preparation of the amyl acetate suspension 

 of the guanin particles was treated in the section of this paper dealing 

 with processes of manufacture of the essence. It is necessary only 

 to dissolve celluloid in such a suspension to make the lacquer. Where 

 the concentrated pasty lacquer is employed, 1 pound is mixed with 

 from 4 to 41/^ gallons of a clear celluloid lacquer containing about 

 20 per cent celluloid. The beads receive from four to six coats of 

 this! Cellulose acetate may have possibilities as a lacquer. It is 

 not affected by a strong light, which. turns celluloid yellowish, it is 

 not inflammable, and is generally quite resistent to external influences. 

 Glacial acetic acid is a good solvent for it, but this solvent is too 

 irritating to the operator and evaporates too slowly for convenient 

 use. 



The selection of the right size grain of guanin particles is a choice 

 of much nicety. Too coarse particles are grainy; slightly finer 

 particles produce too much brilliancy, approaching metallic luster; 

 too fine particles are dull or chalky. The finest orient is given by a 

 moderately fine grain, but since the purchasers' choice varies, all 

 degrees of brilhancy are to be found on the market. 



Various dyes are also used to tint the lacquers. Safranin or 

 eosin produce a pink, vSudan III in very great dilution gives a cream 

 or oriental hue, while Victoria blue will neutrahze any yellow present 

 or give a blue tint. 



The simplest dipping process is to put the bead on a toothpick and 

 dip, revolvmg until the coat fails to run, and then dry. This method 

 is expedited by fixing many toothpicks in a block with fine holes to 

 receive them, and dipping many at a time. Mechanical devices are 

 also in use for dipping automatically. The room in which the 

 dipping is done should be free from dust, and in the larger factories 

 air conditions are controlled to reduce humidity and remove dust. 



ROMAN PEARLS 



Another class of* imitation pearl is made by covering the glass 

 bead with the air-bladder membrane from certain fishes. This 

 membrane or bladder is a colorless tissue composed of a gelatinlike 

 substance, and in many species of fish contains a brilliant natural 

 deposit of the guanin crystals. The air bladder of Argentina 

 sphyrsena is used in the manufacture of ''Roman" pearls. 



' G Leroy et Cie. French patent 473662, Oct. 8, 1914, additions 19477,i 19522, and 20258; also Paisseau, 

 French patent 420885, Dec. 6, 1909. 



