PLASTER CASTS. 



479 



As many of my readers may know, types are very valuable 

 articles, and must not be wasted. If, therefore, a book should 

 bo thought likely to have a steady sale, much of its value would 

 be lost if the types were kept standing, inasmuch as they could 

 not be used for any other work. 



In such cases the Stereotype is employed. Omitting minute 

 details, the process is as follows : 



The type, ready set up, is carefully oiled. Plaster of Paris 

 mixed with water is then poured into a shallow trough, and the 

 type pressed into it. In a short time the plaster hardens, and 

 the type is withdrawn. The plaster mould is then baked, to 



SHELL-CAST IN CHALK- 



CAST DT PLASTER OF PABIS. 



drive off all moisture, and type metal is poured into it. Thus 

 a solid mass is procured, instead of a number of separate pieces, 

 so that there is no danger of disturbance, and the whole block 

 can be multiplied ad libitum if needed. This process sets free 

 the types, which can be broken up and used again. 



The ordinary method of taking plaster casts is nearly the 

 same as that which has been described. The object to be cast 

 is oiled, and plaster of Paris carefully applied to it. When it 

 is " set, "the plaster "mould" is removed and dried. The process 

 is then reversed, the interior of the mould being oiled, and 

 plaster poured into it, so as to produce an exact reproduction of 

 the original. 



IN Nature we have almost exactly the same process, although 

 it is necessarily conducted in a much slower manner. 



