34 V. S, BUREAU OF FISHERIES 



Pearls arc made in a similar manner b}^ the Chinese, who use a wax 

 bead instead of a glass bead. 



A story is related of a Roman lady who felt highly complimented' 

 when an Italian nobleman referred to her as a Roman pearl. Her 

 appreciation of this term gave way to indignation when she learned 

 that the Roman pearl was an out-and-out imitation. 



IMITATION MOTHER-OF PEARL CELLULOID PLASTICS 



Sheet celluloid containing guanin particles to imitate mother-of- 

 pearl for the manufacture of mirror backs, manicune and toilet sets, 

 ladies' fancy canes, opera-glass handles, etc., is now coming into 

 prominence. 



The amyl acetate-celluloid lacquer is brushed or sprayed on glass 

 or polished metallic surface and a grain is worked into it by means of 

 a straightedge, painter's graining tool, or other instrument. Thick 

 sheets so made are split with cutting machines. Thin sheets are 

 made directly on the glass without splitting. The finished sheets are 

 polished under pressure against polished nickel sheets. The pearlj' 

 celluloid sheets are cemented to a white backing sheet, and this in 

 turn to amber, or not, as desired.^" 



DETECTION OF IMITATION PEARLS 



Recognition of a genuine or imitation pearl is somewhat like recogni- 

 tion of a person — a matter of familiarity. Those wdio are at all 

 familiar with pearls can detect imitations at a glance. Yet there 

 are definable differences. The genuine pearl has a specific gravity of 

 about 2.6; its surface is usually somewhat iridescent, giving a faint 

 play of colors; its surface does not give a sharp and well-defined 

 reflection of such things as window bars ; the hole is obviously drilled ; 

 the genuine pearl can be scratched by a sharp knife; it is opaque. 

 It is not affected by acetone or amyl acetate but is readily attacked 

 by acids. 



The hollow glass bulb imitations are glass outside ; the}^ give a sharp 

 reflected image of window bars; they can not be scratched except 

 with things that will cut glass; the holes are plainly holes in glass 

 with smooth edges, and usually one is larger than the other. They 

 are usually light and often float on water; they have no iridescence, 

 or else have too much; and the surface is not attacked by any acid 

 but hydrofluoric. 



The solid or "indestructible" pearl is made of opalescent glass; it 

 is usually translucent and looks yellowish when held up to the light; 

 it may even give an image of objects like a lens. The coating is 

 outside and does not extend smoothly up to the very edge of the 

 hole. Air bubbles may often be detected in the glass. The coating 

 is celluloid and can be cut or peeled off, and* is inflammable; it 

 can be dissolved off with amyl acetate or acetone. If a pearl sus- 

 pected to be this type of imitation, but claimed to be genuine, is 

 immersed for a minute or two in acetone, the genuine will not be 

 damaged but the coating will dissolve off from the imitation. 



1° For review of literature and bibliography of imitation mother-of-pearl, see Von Unruh, 1918a, 



