THE POTTER'S ART. 



and when this is the case, the mineral is raised and prepared for 

 the potter's use. 



15. The following is the method of preparation : The stone, 

 having been broken by a pickaxe, is laid in a stream of running 

 water : the light argillaceous parts are thus washed off and kept in 

 suspension ; the quartz and mica being separated are allowed to sub- 

 side near the place where the stone was first raised. At the end of 

 these rivulets are a kind of catchpools, where the water is at last 

 arrested, and time allowed for the pure clay with which it is charged 

 to form a deposit, which, being effected, the water is drawn off ; 

 the clay is then dug up in square blocks and placed upon a number 

 of strong shelves, called "linnees," so fitted as to allow of the free 

 circulation of air, that the clay may be properly dried. Thus pre- 

 pared, it is an extremely white mass, capable by being crushed to 

 be reduced to a fine impalpable powder. In this state it is sent to 

 the potteries under th6 name of China clay. 



16. One of the departments of this manufacture, in which 

 England has of late years gone considerably in advance of the con- 

 tinent, is that devoted to the fabrication of statuary porcelain. 

 This beautiful branch of reproductive art has been almost created 

 within the last six or seven years by some of the most eminent and 

 enterprising establishments in Staffordshire. 



Like all novelties in the arts, this process has undergone a suc- 

 cession of improving changes. At first the statuary material was 

 limited to a thin superficial coating laid upon a common body. At 

 present, however, the object is composed of one homogeneous mass 

 of statuary porcelain. The articles thus produced are superior in 

 quality, but much more difficult of manufacture, owing to the 

 much greater degree of contraction which takes place in the oven, 

 and the consequently increased chances of distortion and fracture, 

 especially in pieces of complex form and considerable magnitude. 

 The contraction of the linear dimensions amounts to as much as a 

 fourth of the original magnitude, so that a figure, which as moulded 

 or cast is four feet high, comes out of the oven definitively only 

 three feet in height, the other dimensions being decreased propor- 

 tionally. The actual contraction in the cubical dimensions which 

 corresponds to this is more than one half, so that the baked 

 materials are included in less than half the space occupied by the 

 unbaked. 



17. The process by which statuary porcelain is produced is that 

 called casting, and it resembles in many respects that by which 

 casts of objects are produced in metal. 



If the object to be produced is such as can be cast in a single 

 piece, a mould of its form is made in plaster of Paris, consisting of 

 two parts which can be united by perfectly plane and smooth 



