PEARL ESSENCE: ITS HISTORY, CHEMISTRY, 

 TECHNOLOGY ' 



AND 



By Harden F. Taylor 



Formerly Chief Technologist, U. S. Bureau of Fisheries 



CONTENTS 



Page 



Introduction - 15 



Terms used 16 



Historical. 16 



Early history 16 



History of chemical research on pearl essence. 17 



Recent history 19 



Sources and distribution of guanin among ani- 

 mals 19 



Production of guanin by animals 19 



Guanin in fishes 20 



E uropean sources of pearl essence 20 



American sources of pearl essence 21 



Properties of pearl essence 22 



Physical properties 22 



Optical and crystallographie properties. 23 



Chemical properties 24 



Processes of making pearl essence. . , 25 



A queous suspensions 25 



Nonaqueous suspensions an! lacquers 26 



Page 

 Chemical examination and assaying of pearl 



essence 28 



Quantitative estimation of guanin 28 



Microscopic examination 29 



Physical analysis of the specimen 29 



Covering power 30 



Manufacture of imitation pearls 30 



Hollow glass imitation pearls 30 



Glass bulbs -. 30 



Production of iridescent effect 31 



Coating the hollow beads inside 31 



Solid or "indestructible" imitation pearls... 32 



Glass beads 32 



Pearl coating 32 



Roman pearls.. 33 



Imitation mother-of-pearl celluloid plastics 34 



Detection of imitation pearls 34 



Bibliography 35 



INTRODUCTION 



The value of a pearl resides not in the material of which it is 

 composed but in the manner in which nature arranges this material. 

 Except in shape, the genuine pearl is identical with the shell or mother- 

 of-pearl of the moUusk that produces it. Both consist of layers of 

 crystalline calcium carbonate alternating with layers of conchiolin, 

 a horny, organic substance that binds together the layers of calcium 

 carbonate. These otherwise worthless materials are so disposed in 

 a pearl as to give an optical effect that makes it one of the most 

 valuable of all articles of commerce. 



To imitate pearls man must make use of some substance that, 

 when put into the shape of a pearl, exhibits a pearly luster.^ The only 

 substance that has ever answered this requirement satisfactorily is 

 the silvery substance deposited in the skin of many species of fish. 

 This substance, when rubbed off the scales, freed from foreign matter, 

 and suspended in water or other suitable liquid, is pearl essence. 

 When applied on the inside of hollow beads or on the outside of solid 

 ones it imitates the genuine pearl quite satisfactorily and makes the 

 ordinary imitation pearl of commerce. When incorporated properly 

 in celluloid plastics, it makes the imitation mother-of-pearl now 



« Appendix II to the Report of the U. S. Commissioner of Fisheries for 1925. B. F. Doc. 989. Techno- 

 logical contribution No. 22. 



2 For data on and discussion of the nature of pearly luster, see Liesegang (1915), Pfund (1917), and Ban- 

 croft (1919). 



15 



