32 U. S. BUEEAU OF FISHERIES 



the speed of revolution doubled, and a small gas flame placed under 

 it until the solvent is evaporated. The coating that adheres to the 

 outside also is removed by working the beads around in a leather bag 

 until they are clean. 



These hollow beads have certain advantages over the "inde- 

 structible" solid ones. The outer surface is of glass and is not subject 

 to the efl'ects of moisture and discoloration. On the other hand, they 

 are usually light in weight and are more readily broken then the solid 

 ones. 



SOLID OR "indestructible" IMITATION PEARLS 



These beads are solid glass with the necessary holes through them 

 and coated on the outside with a waterproof lacquer containing the 

 lustrous material. 



GLASS BEADS 



The glass beads from which solid imitation pearls are made are 

 opal — neither milk-white nor clear. The exact degree of opalescence 

 has much to do with the appearance of the finished bead, and is 

 varied in practice to give the desired tint, some being almost white, 

 others being almost transparent. The material is usually glass tubing 

 of the required degree of opalescence and of capillary bore, the size 

 necessary for stringing. 



The beads may be made in several ways. The tube is cut into 

 lengths to give pearls the desired shape when finished. These pieces 

 of tube are strung on small iron or copper wire (the writer has used 

 strands of asbestos thread), and they are then held in a gas flame 

 and rotated as they soften, until they assume the desired globular 

 shape. They are removed from the flame and rotated until cool. 

 If wire was used as a support, the beads are put in a bath of dilute 

 nitric acid to dissolve out the wire. If asbestos was used, it may be 

 punched out with a bodkin. Bonnet ^ coats a revolving m.etallic 

 shaft with a refractory kaolin mixture, which is pulverulent when dry. 

 The molten glass is applied to the revolving shaft in drops and the 

 shaft revolved until the beads are shaped. When they are cool, the 

 shaft is pulled out of the beads. 



A more rapid method of making the beads is as follows : The glass 

 tube of chosen caliber is cut into suitable lengths to make the beads. 

 These pieces are tumbled in a mixture of fire clay and graphite until 

 the holes are plugged with the mixture. They are then introduced 

 into an iron drum containing powdered talc. This drum is slowly 

 revolved while it is heated until the glass is soft. The pieces assume 

 the desired globular shape during the revolving and the talc prevents 

 them from sticking together. They are cooled while still being 

 revolved. They are then taken out and are ready for the coating, 

 when the refractory material is removed from the holes. 



PEARL COATING 



There are many variations in the coating process which this paper 

 will not attempt to describe exhaustively. Most of them are trade 

 secrets, and some are covered by patents. 



> L. Bonnet, United States patent 1466575, Aug. 28, 1923. 



