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. 
