30 U. S. BUREAU OF FISHF.KTES 



thi'ough a tared Gooch crucible densely packed with fine asbestos 

 (or other suction filter), repeating the filtration until the filtrate is 

 as clear as possible. Wash the filter with more acetone. Transfer 

 the acetone filtrate to a tared evaporating dish and evaporate at 

 moderate temperature to constant weight. Excessive temperature 

 must be avoided to prevent loss of any camphor from the celluloid. 

 Weigh the celluloid and record. Ignite the crucible and weigh the 

 ash. A further separation of the constituents of the ash may be 

 made, if necessary, by the usual methods. 



C0VERIX(;! POWEIl 



A practical test used by manufacturers is to mix the specimen 

 under consideration with the lacquer or plastic and apply in the 

 customary way in making pearls or nacreous celluloid sheets, and 

 compare the results with their own standards. Since practices differ 

 so widely, it is impossible to give any details of the methods used for 

 these tests. 



MANUFACTURE OF IMITATION PEARLS 



From the historical account it was seen that the beghining of 

 imitation pearl manufacture was made by Jac[uin with solid beads 

 coated on the exterior with pearl essence and glue (the bead itself 

 was wax, alabaster, or glass), but because of the lack of resistance 

 of the gluey coat of ]3earl essence the beads were not satisfactory. 

 To overcome this difficulty, the early bead makers (Jaquin or his 

 immediate successors) had recourse to hollow glass bulbs coated on 

 the inside, as described by Beckmann. It was something like 250 

 years later that, on the invention of waterproof lacquers, the art 

 returned to Jaquin's original idea of coating a solid bead on the out- 

 side in the manufacture of so-called ''indestructible pearls" of the 

 present day. However, both the hollow and solid pearls are now 

 on the market. 



HOLLOW GLASS IMITATION PEARLS 

 THE GLASS BULBS 



The hollow glass beads for this type of pearl are of two general 

 classes. The very cheap imitation pearls, such as those used for 

 necklaces, usually sold in 5 and 10 cent stores, are made of molded 

 beads. A glass tube is blown in a mold making a number of con- 

 nected bulbs, which are cut apart after the glass cools. These beads 

 on examination show mold marks and ridges on opposite sides of 

 the bead, extending from one hole to the other. They also have 

 extensions around the holes where they have been cut apart from 

 their neighbors on the original molded piece. The cut edges are 

 sharp, and the spherical parts of the beads arc not close together 

 as they are in the case of beads of better (juality. 



These beads are coated inside first with pearl essence and gelatin. 

 When this coat is dry, the bead is filled with paraffin or other suit- 

 able wax. Such beads are very light and will usually float on water. 

 They are of good but artificial-looking luster. Other ornamental 



