BOHEMIAN GLASS. 351 



pot, which is kept warm by a moderate flame and serves the purpose 

 of a cooling-vessel. 



The button, or whatever is the article manufactured, is still only in 

 the rude state, with the edges yet rough and the surfaces uneven, but 

 already provided with holes for the after-insertion of metallic eyes. 

 The rough edges are smoothed away by grinding on the grooved 

 periphery of a wet sandstone, being held to it by a wooden clamp 

 which is managed by the right hand while it is turned with the left. 

 The surfaces are ground with wet sand on horizontal, fast-turning iron 

 plates, and afterward polished on the face of soft wooden wheels 

 roughened with Tripoli dust. To speed the operation, the workman 

 presses upon the piece with both hands and gives it a peculiar rotary 

 motion that equalizes the stronger friction to which the parts nearest 

 in contact are exposed. The proper application pf this movement is a 

 matter of knack, and is founded on mathematical principles, which 

 also appear when the object is rubbed on a solid base, in the epicy- 

 cloid lines which it is made to describe. On account of the relatively 

 long time required for the operation of polishing, the smaller articles 

 are subjected to what is called a fire-polishing, in which the smoothly 

 ground pieces, imbedded on a plate of clay in fine sand, are heated in 

 a muffle till their surface runs. If more strongly curved plates are 

 wanted, to form a rose, for instance, the disks, previously prepared by 

 notching and perforation in the middle, are placed in funnel-shaped 

 crucibles in the hot muffle. The central part of the disk sinks on being 

 heated. The hollowed leaves are then set one in another, in the order 

 of their diminishing size, and fastened together by a glass-headed 

 pin. 



The foundation of the design is formed of a brass plate which has 

 been previously shaped and perforated. Additional decorations are 

 given by means of little beads, which are melted off in the glass-blow- 

 er's lamp from thin threads of glass, and find their places in minute 

 holes in the plate. Black sealing-wax is added to heighten the gloss 

 and the blackness, as well as to cement the parts together. In other 

 cases lighter figures are made by partly polishing or by etching them 

 out on the smooth background. Iridization of beads, buttons, etc., 

 has been much in vogue for a few years past ; by this process those 

 articles are given a metallic appearance. The luster of gold or silver 

 is imparted by covering the black glass with a silver- or gold-leaf var- 

 nish and afterward heating moderately in a muffle. Peculiar tarnish- 

 effects are given by the application of what are called luster-colors ; 

 and, lastly, these are shaded by a brief treatment with chloride-of-tin 

 vapor. The glass articles, hung upon a wire, having been previously 

 warmed in the muffle-furnace, are drawn through the thick white 

 vapors which are formed when a spoonful of the tin-salt is dropped 

 upon red-hot iron. A long experience and considerable manual dex- 

 terity are required to make sure of getting the particular iris-color 



