BORATES. 323 



ware. Porcelain is, however, commonly glazed to add 

 to its beauty. 



822. GLAZING. Earthenware after its 



Describe tlie 



process of first baking is porous, and therefore unfit 

 glazing. ^ mogt useg ^ or W j 1 ' c j 1 ^ j s intended. It 



is subsequently covered with a thin paste formed of 

 the constituents of glass. Being then subjcted a 

 second time to the heat of the furnace, a thin glass 

 or glaze is formed upon the surface. The glazing 

 of certain wares is effected by exposure at a high 

 temperature to vapors of common salt. A double de- 

 composition ensues with the oxide of iron which the 

 ware contains, by which soda is formed. This imme- 

 diately fuses with the silica and other materials to form 

 the glaze. The chloride of iron which is formed at 

 the same time passes off as vapor. A paste of pounded 

 feldspar and quartz, to which borax is sometimes added, 

 is employed in glazing porcelain. 



823. PORCELAIN PAINTING. Metallic 

 of 'porcdTin oxides form the basis of the pigments used 

 painting? n p a j n t m g upon porcelain. The color- 

 ing effect of the different pigments is mentioned in the 

 chapter on metallic oxides. The patterns on ordinary 

 .earthenware are first printed on paper, and then trans- 

 ferred, by pressure, to the unglazed ware. The paper 

 is afterwards removed by a wet sponge. 



BORATES. 



What is 824. BORAX. Borax is the only impor- 



lorax? tant salt among the compounds of boracic 



