GLASS 



2509 



GLASS 



about forty per cent of the thickness is elim- 

 inated, the resulting sheet being from "one- 

 fourth to three-eighths of an inch thick. 



To make wired plate glass a wire netting 

 is placed between the surfaces of the sheet 

 while the glass is soft; the result is a strong, 

 almost unbreakable pane, extensively used as 

 a fire protection around elevator shafts and 

 where there is danger from too close crowding 

 of buildings. Basement and other windows 

 that are liable to be broken easily are also 

 frequently made of it. 



Glass Tableware. A large part of the or- 

 dinary glassware that appears on the table is 

 made by pressing. The press consists of an 

 iron mold, containing the design and orna- 

 mentation of the article to be made, and a 

 plunger which is worked by a lever. The 

 gatherer places an iron rod into the molten 

 glass, bringing out a quantity of the substance 

 on the end of it. From this lump enough 

 glass is cut to make the article, and the mass 

 is dropped into the mold and pressed into 

 shape by the plunger. When this process is 

 completed the article is taken out and an- 

 nealed. Some articles are made in two parts; 

 in manufacturing a goblet, for instance, the 

 bowl is shaped in one press and the stem in 

 another. A good deal of the more expensive 

 tableware is made by blowing. In many fac- 

 tories machines operated by compressed air 

 take the place of the human blower. 



Cut Glass is the most expensive and ornate 

 tableware in use. The object is first cast in a 

 mold or is blown, and its plain surface is then 

 marked with the chosen design. It is next 

 held against an iron wheel with sharp edges, 

 which is mounted on a horizontal axis, and 

 which cuts the design into the glass. The 

 face of the wheel is kept supplied with coarse 

 sand and water, which drips from a hopper 

 above. It is not always necessary to trace 

 the design before it is cut into the surface, for 

 a workman of special skill and training is able 

 to complete the work with only his eye for 

 a guide. After the design is cut the article is 

 held against a wheel of sandstone, which is so 

 shaped as to have a sharp edge in the middle. 

 The action of this wheel smooths the edges 

 and surfaces made by the cutting wheel; dur- 

 ing the process a small stream of water con- 

 stantly plays upon it. A wooden wheel sup- 

 plied with pumice stone next gives a finish 

 and polish to the object, and it is finally 

 cleaned by means of a brush made of spun 

 glass. When all the tiny fragments of glass 



are removed from the grooves and crevices, 

 the article is washed and is then ready for 

 the market. 



Bottle Glass. For the methods used in mak- 

 ing bottles see the article BOTTLE, subhead How 

 Bottles Are Made. 



Colored Glass. Oxides of different metals, 

 which are added in small quantities to the 



SPECIMENS OF CUT GLASS 



usual ingredients, give glass its various colors. 

 Iron produces a pale yellow or a pale green; 

 manganese, a pink, amethyst or violet. Copper 

 gives a deep green or deep blue, but by adding 

 a reducing agent to take the oxygen from the 

 oxide, the metal copper can be set free in 

 extremely minute particles. This imparts a 

 ruby-red color to the glass. A still finer ruby 

 glass is made by using gold in place of copper 

 oxide. A rich blue is produced by cobalt 

 oxide, a milky white by tin oxide, calcium 

 fluoride or bone ash, and many beautiful tints 

 by a combination of the various coloring sub- 

 stances. The exquisite stained-glass windows 

 of many great churches are mosaics of different 

 colored glass, cut and fitted so as to produce a 

 complete design. On others the pictures are 

 painted, and the colors are then burned into 

 the glass. Colored glass, cut into small pieces, 

 is sometimes seen in the ornamental mosaic 

 work that beautifies the interior of public 



