PEAEL ESSENCE 31 



objects such, as pear-shaped beads for stickpins, lion's heads, and the 

 like, blown in glass, are made by the same general method. 



The better grade of hollow necklace beads are made of a specially 

 selected soft but colorless glass tubing. The ordinarj^ laboratory 

 glass tubing is not satisfactory. One method of making these bulbs 

 is to flame-seal the tube at one end and blow a bulb of the desired 

 size and shape. A sheet metal mask is made with a hole somewhat 

 larger than the hole desired to be made in the bead. The bead is 

 pressed against this mask and a sinall pointed blast flame is directed 

 against this hole. This will soften the glass at a very small point. 

 A hole is blown through, and an instant in the flame is allowed for 

 the edges of the hole to retract and become smooth. The bead is 

 then cut away from the glass tube. The hole at the cut end may also 

 be smoothed in the flame with the aid of the mask. Usually in beads 

 of this class the two holes are unlike, the wall being thinner around 

 the hole that was blown than around the other. Sucli beads, when 

 strung into necklaces, come close together and have a good ap- 

 pearance. 



These beads, after having been coated inside with the pearl es- 

 sence mixture, are filled with wax, equal parts of paraffin and Japan- 

 ese white wax being suitable. Sometimes barium sulphate is added 

 to the wax to give more weight and whiteness, but this can be over- 

 done. 



PRODUCTION OF IRIDESCENT EFFECT 



Iridescence is usually absent from imitation pearls. However, 

 in the case of the hollow-bulb type an iridescence is sometimes 

 imparted by a judicious treatment of the bead with hydrofluoric 

 acid or by coating the bulb with a solution of titanium cliloride and 

 heating in the Bun sen flame. These eft'ects are such an exaggerated 

 and shiny iridescence that they rather impair than improve their 

 resemblance to genuine pearls. 



COATING THE HOLLOW BEADS INSIDE 



The method of coating these hollow beads inside varies greatly. 

 The classic method is to revolve the bead on a toothpick, either by 

 hand or machine while the essence mixture is introduced through 

 the open hole by means of a fine pipette. The bulb is revolved until 

 the coating is uniform. The writer has made this inside coating with 

 a gelatin solution so concentrated that it readily sets on cooling. 

 It may be preserved with 0.3 per cent salicylic acid to prevent de- 

 composition during the slow drying that follows. When the hot 

 liquid is introduced into the bead the latter is revolved until a uni- 

 form coat is obtained. A small camel's-hair brush, wet with ether, 

 is touched to the outside while the bead is still revolving. Rapid 

 evaporation of the ether cools the bead until the gelatin sets. 



Parkert (1919) describes a method of coating these beads in large 

 quantities. He makes a quick-drying lacquer of copal lac, mastic, 

 and acetone, into which the dried lustrous material is incorporated. 

 The lacquer is put in a bowl that can be heated and revolved at the 

 same time. The bulbs are placed in the vessel with the lacquer and 

 the vessel is sealed and revolved until the lacquer has found its way 

 into all the bulbs and little is left outside. The vessel is then opened, 



