258 Porcelain and Earthenware. 



lavender is preferred in some of the French manufactories as a ve- 

 hicle; at Sevres gum water is substituted for the volatile oil; oil of 

 turpentine is generally used in England. By due combinations of 

 the vitrifiable colors, every shade may be obtained ; but to insure 

 success, it requires on the part of the artist great judgment and skill 

 in combining materials with reference to their chemical action on one 



another. 



Colors should be pounded quickly in a covered glass or agate mor- 

 tar, and as much care used in rubbing them on the palette as for 

 miniature painting : and the fluidity of the mixture should be kept 

 exactly at the point where the finest strokes can be produced with 

 facility. When the paintings are finished, the pieces are put in the 

 enamel furnace at a low heat, just sufficient to vitrify the flux with 

 which the colors are incorporated. If the execution proves imper- 

 fect, they are retouched and burned in again and again, until they 

 are satisfactory to the artist. Eight or ten hours firing are sufficient 

 in the enamel kiln, to burn the colors into the glaze. From the fore- 

 going details it appears that three degrees of heat are required in 

 the different processes of firing porcelain. The heat to which it is 

 subjected in the state of biscuit, is raised to the highest point which 

 the ware will bear : the next firing is to unite the glaze or enamel 

 with the body of the ware and must be only sufficient to vitrify the 

 covering, and so far soften the body, as to cause the union of the 

 glaze with the surface pores of the ware ; again, the comparatively 

 low heat of the enamel kiln, must be raised only so high as to vitrify 

 the flux in which the colors are embodied, and to soften the glaze 

 so far, as to permit the colors to unite with it, as the glaze did with 

 the body of the ware in the preceding furnace. 



Porcelain is gilded by the use of gold in leaves, and by reducing 

 it to powder with a solution of aqua regia after which it is mixed with 

 gum water and applied with a brush. The fire causes the oxygen 

 to fly off*, and restores the gold to its metallic state. Japanners size 

 moistened with oil of turpentine, is spread on parts designed for leaf 

 gold, and when nearly dry, it is laid on with cotton wool. In both 

 cases it is burnt into the glaze in the enamelling kiln. It is then 

 burnished with agate or blood stone, and rubbed off with white lead 

 and vinegar, which is the final process in the manufacture of por- 

 celain. 



