3 i2 THE POPULAR SCIENCE MONTHLY. 



more plastic as it grows older. The qualities required of a good paste 

 may be communicated by diluting it and stirring it with water and 

 decanting, or by prolonged beating and manipulation. By treading it 

 out or beating it we not only give it complete plasticity and homoge- 

 neity, but we also clear it of air-bubbles which would otherwise swell 

 out in baking and cause much damage. 



The next thing is to give our ware the form which has been deter- 

 mined for it in a design previously made. This requires a knowledge 

 of the whole process of fabrication. It would be a mistake to suppose 

 that porcelain can be baked in any desired form. It becomes soft in 

 baking, and has to be supported ; and, as it is to be covered with a glass 

 that melts at the same moment, places which need not be enameled 

 must be found for fixing the supports in every piece, unless we are 

 willing to risk having it spoiled. We may thus comprehend one of 

 the difficulties in the manufacture of porcelain, and one of the points 

 in which it differs most from delf. 



Articles of porcelain may be shaped without molds or with them. 

 By the former method all the shapes are obtained that may be pro- 

 duced by turning. The clay is first shaped on the wheel by the hand 

 into a rough block of the general shape which the object is destined 

 to assume, and is then left to dry, slowly and with care, to keep it 

 from cracking. When it has been dried to a suitable degree of con- 

 sistency, it is put upon the wheel again and carefully worked into the 

 exact shape desired, with the moldings and ornaments called for by 

 the design, and by the aid of the most simple instruments. 



Articles whose shape does not adapt them to manipulation on a 

 revolving wheel, such as objects of statuary and many lighter objects, 

 may be shaped by molding them. The mold is made of plaster of 

 Paris ; to it, when dry, is applied a layer of the porcelain paste, which 

 is pressed into it carefully and as evenly as possible ; the earth espouses 

 all the details of the sculpture, and, after a few moments, the plaster 

 having absorbed the water from the paste in contact with it, a shrink- 

 age takes place, thanks to which the proof detaches itself almost spon- 

 taneously. The operation is sure to be successful in the case of simple 

 forms whose outlines offer no impediment to taking them from the 

 molds. If, however, we purpose to obtain objects in relief, statuettes, 

 groups of figures, or sumptuous vases, the sculptural decorations of 

 which constitute their chief ornament, the process becomes more com- 

 plicated. In this case the molder has to divide his pattern into a 

 number of parts, the superficies of which must be determined by the 

 possibilities of taking off the molds ; then he must make as many 

 molds in plaster as he has parts of his model ; these molds will in 

 their turn serve for the reproduction of each of the parts, which have 

 afterward to be joined and cemented by the aid of the paste diluted 

 in water. After this the seams at the junction of the parts must be 

 rubbed away, and the whole work finished up by a restorer who must 



