PORCELAIN AND THE ART OF ITS PRODUCTION. 313 



necessarily be an artist. I can not leave this part of my subject with- 

 out mentioning the property which porcelain has of shrinking when 

 baked. The shrinkage amounts to about ten or fifteen per cent. 



A third method of shaping porcelains is by casting, which was dis- 

 covered at Tournay, 1784, and in which Brongniart has made numer- 

 ous improvements. Nothing is more simple than the manufacture of 

 a small object by this process. Thus, if we take a plaster mold of a 

 cup, and pour into it a quantity of barbotine, or porcelain-clay mixed 

 with water, the mold will absorb the water from the clay in contact 

 with it, forming a shell less liquid than the rest of the barbotine, and 

 which sticks to the plaster. When this shell has attained a suitable 

 thickness, the rest of the barbotine may be poured out : what remains 

 in the mold constitutes the cup. We leave it to dry, and in a little 

 while it will have gained consistency enough to be taken out of the 

 mold without being deformed. Ware thus made is extremely delicate ; 

 the slightest pressure with the lingers may destroy it. This process is 

 used at Sevres for large pieces, but special manipulations are required 

 for such work ; for the weight of the shell which should adhere to the 

 mold when the liquid is poured out, and which should be thicker and 

 heavier in proportion to the greater size of the vessel, is very apt to 

 cause it to separate from the plaster and fall. The least awkward- 

 ness might destroy the piece, and this should be avoided at any cost. 

 MM. Milet and Delacour have devised a method, which has been used 

 at Sevres since 1857, for avoiding such accidents by turning compressed 

 air against the interior of the mold at the moment the barbotine is 

 poured out, to take the place of the liquid and hold the porcelain shell 

 against the plaster. M. Regnault has simplified this operation by ex- 

 hausting the air on the outside of the mold, which effects the same 

 purpose and is more convenient of execution. The absence of seams, 

 the purity of the outlines, and the clearness of the surfaces obtained 

 by this process, make it one of inestimable value when we wish to get 

 an object of art, and lift it far above the process of molding. The de- 

 tails of the operation are very exacting, but none of them should be 

 neglected. Their importance may be realized by reflecting that a hid- 

 den fault in the interior of a large piece, a bubble of inclosed air, a 

 lack of homogeneity in the paste, or other flaw, is not perceptible till 

 after the baking, when the vessel has been decorated, and may perhaps 

 have become of very great value. The slightest defect in the casting 

 may destroy this value. 



The objects, having been properly shaped and fitted, have next to 

 be transformed into porcelain by the action of fire, the function of 

 which is to combine the different elements of the paste and deter- 

 mine the fusion of the glazing. The baking is done twice. In the 

 first operation, when the temperature is relatively only moderately 

 high (1,800 to 2,160), the earth is converted into what is called biscuit- 

 baked porcelain; it becomes very tough and sonorous, and extremely 



