i 7 4 THE POPULAR SCIENCE MONTHLY, 



rendered more complete and more uniform by the rotary move- 

 ment of the axle. The globes have now only to be washed, and 

 nothing further remains but to sell them. The etching process is 

 completed. 



The solution of hydrofluoric acid leaves the etched portions of 

 the glass transparent ; but if some alkaline salt, such as ammonium 

 or potassium sulphate, be present in the bath, the etched portions 

 are rendered opaque. This reaction is utilized to obscure globes, 

 in place of the grinding process already described. The globes 

 have only to be dipped into such a bath for a moment or so, to be 

 thoroughly obscured. As both sides of the glass are acted upon, 

 the process of chemical obscuring is only used where the globe is 

 not to be further decorated. In this same department the opera- 

 tion of "bisquing" is being carried on. If opalescent glass or 

 colored translucent glass be dipped into such an alkaline bath for 

 a brief, time, it will take the dull finish characteristic of bisque. 

 Thousands of the so-called fairy lamps, in red and pink and blue 

 opalescent glass, are treated in this manner. Glass surfaces 

 which are subsequently to be painted on are also bisqued in order 

 to facilitate the process. A very brief immersion makes the sur- 

 face sufficiently rough to write on with an ordinary lead-pencil 

 without the least difficulty. The large white plaques exposed for 

 sale in the art-stores are prepared in this manner. The bath is 

 contained in large wooden tanks, and the articles are simply 

 dipped in by hand. 



The products of all these processes — of cutting, engraving, 

 grinding, and etching — are all more or less beautiful. The highest 

 excellence is attained, however, when the several processes are 

 combined in the production of the once greatly admired cameo 

 glass. The best of this is now manufactured in England, but it 

 has also been made, though with less success, in America. 



The prototype of this variety of glass is the celebrated Port- 

 land vase, with whose history and mishaps most people are famil- 

 iar. It was found about the sixteenth century in a sarcophagus 

 in the neighborhood of Rome, and for more than two centuries 

 adorned the salon of the Barberini family. When their collection 

 was sold, the vase was purchased by the Duchess of Portland, for 

 eighteen hundred and seventy-two pounds, and was loaned to the 

 British Museum. Even in such safe keeping it came very near 

 complete destruction at the hands of a madman named Lloyd, 

 who gave it a heavy blow with a stick. It has since been repaired 

 with such ingenuity that one can scarcely distinguish the numer- 

 ous fractures. The vase is supposed to date from the time of the 

 Antonines, and is one of the finest examples of ancient glass-mak- 

 ing extant. The body is of a deep-blue color and the raised 

 figures are of opaque white. For many years archaeologists be- 



