3 i6 THE POPULAR SCIENCE MONTHLY. 



divided into two classes : decoration by the sharp-fire, and decoration 

 by the enameling furnace. The former method consists in the appli- 

 cation upon the porcelain of coloring substances which are fixed 

 and developed upon it at the same temperature as that at which the 

 porcelain is baked. It is the method that gives the most highly prized 

 results, for with it the color is covered by the enamel, and takes a 

 high luster and deep setting, becoming, as it were, of one body with 

 the object. The magnificent blue of Sevres, certain browns, the 

 blacks, and a few other shades are obtained by this process. 



The color may be mixed in the paste, or put on the fashioned ob- 

 ject, before enameling, or mixed with the glazing ; or it can be put 

 upon porcelain that has been baked and will then be baked a second 

 time in the sharp-fire. This is the process we employ at Sevres for 

 our blues. 



One of the most brilliant varieties of decoration by the sharp-fire 

 consists in what is called the process of applied pastes, or in painting 

 with barbotine upon the raw or biscuit-baked porcelain ; by succes- 

 sive, rightly tempered applications we can lay on a considerable thick- 

 ness of material, on which the artist can with the chisel give a fine 

 finish and thus add great value to his decoration. When the barbo- 

 tine is applied upon a tinted bottom, charming effects, making the 

 porcelain look like real cameos, can be obtained in the clear material. 

 If coloring oxides are added to the barbotine, a real picture can be 

 obtained. Unfortunately, the number of colors that can be used in 

 the sharp-fire is, on account of the excessive temperature, very limited. 



In decoration in the enameling-furnace, the painting is always 

 done on baked porcelain, consequently on enamel, and the heating 

 takes place at a relatively low temperature. Since the glazing is not 

 to be melted, as in the sharp-fire, an intermediate agent or flux is 

 required to make the colors adhere. This is generally a silicate or a 

 silico-borate of lead, or for metals a sub-nitrate of bismuth. When 

 the temperature is raised, these substances melt, attack the glaze, and 

 combine with it, determining by their reaction the adherence of the 

 color. The temperature in these operations is determined by the 

 nature of the fluxes and of the colors ; and, as some colors are more 

 sensitive than others, it is frequently necessary to bake in two succes- 

 sive and different fires. 



The palette of Sevres is complete, and is competent to reproduce 

 with a marvelous excellence the chief works of the greatest painters. 

 Notwithstanding the beauty of the sharp-fire colors, and the richness 

 of the palette, much is still left to be desired in the decoration of 

 French hard porcelain. The sharp - fire colors are too limited in 

 number and too delicate to admit of any great variety of effects being 

 drawn from them ; and the colors of the enameling furnace, in spite 

 of their richness, have a capital fault. They are opaque, and they 

 cover the porcelain and hide all of its highly prized qualities. 



