POTTERY 



361 



a different construction, the Cornish granite and 

 calcined flints are reduced to a somewhat similar 

 state. This mill is very strongly constructed, and 

 consists of a tub-like vat, A, in the centre of which 

 turns an axle, B, moved by machinery ; in the 

 bottom of the vat is a thick stone-bed, C, consisting 

 of either chert or horn stone. From the upper part 

 of the axis three strong arms, D, D, D, project 

 like the spokes of a wheel ; and strongly attached 

 to these are stout beams, a, pointing downward, 

 and nearly touching the stone-bed, C. As the axis, 

 with its arms and beams, turns round, the beams 

 push some large masses of the Cornish granite or 

 of chert stone round with them, and these triturate 

 the calcined flints and other hard materials, and 



Fig. 2. 



tir up the water with which the vat is kept con- 

 stantly supplied, whilst it overflows in a milky 

 state, charged with the finely-divided materials, 

 into a cistern, where it is kept stirred until it is 

 sufficiently supplied with the solid materials, and 

 the thickened milky liquid is then drawn off, in 

 proper proportions, into a vat to which the pre- 

 pared clay is also passed. The mixture of the two 

 is then allowed to subside until the water is nearly 

 clear, when it is drawn off; and the sediment is 

 deprived of its surplus moisture, either by evapora- 

 tion, or, in the best works, by a pneumatic 

 exhausting apparatus, which does it very quickly. 

 The composition is then a fine plastic material of 

 the consistency of tough dough, and is ready for 

 the potter's use. In preparing the finer materials 

 for porcelain many other operations are required, 

 all, however, having the same object viz. the 

 extremely minute division of the substances used. 



The prepared clay is taken to the throwing- 

 machine, or potter's wheel, which is represented in 

 t g. 3. This consist* of a fixed table, A, through 



Fig. 3. 



which passes the axle, B, and rises a little above its 

 surface, and having on its upper end a disc, C, 

 which revolves with it. The axle is put into rapid 

 motion by turning the fly-wheel, D, either by hand 

 or machinery ; and this causes a rapid revolution of 

 the disc, C, upon which is placed the soft mass of 

 clay to be moulded. At E is seen an upright, with 

 a small gliding-bar regulated by a screw ; this is 



the guide for the potter to regulate the height of 

 the vessel he is malting. When the lump of clay is 

 revolving, the potter, 

 with his hands or with 

 proper tools, fashions it 

 into any rounded form 

 he desires, gradually 

 working from the base 

 upwards till the vessel 

 in his hands attains the 

 external shape, height, 

 and thickness of wall 

 required. It is then put 

 aside for some time to 

 dry, and when in a state 

 of greatest doughy ten- 

 acity it is fixed on a Fig. 4. 

 turning-lathe, and by 



means of sharp steel tools its surface is accurately 

 turned and smoothed. But some articles are 

 formed in moulds, the moulds being made of plaster 



Fig. 5. 



Fig. 6. 



of Paris. This answers well for fine porcelain in- 

 tended to be very thin, because the plaster-mould 

 absorbs much of the moisture in the paste, and 

 thus partially dries it, so that it admits of hand- 

 ling, which in a softer state, would be very difficult. 

 The paste is used so liquid 

 that it can be poured into 

 the moulds. It is usual, in 

 casting, to have a mould for ] 

 each part, as seen in figs. 4, 

 5, 6, which represent the 

 body, neck and lip, and foot 

 of the cream-ewer, fig. 7. 

 The handle is also separately 

 moulded, and attached with 

 the aid of a fluid clay paste, 

 called a slip. For nearly 

 flat articles, such as dinner- 

 plates, a plan is adopted 

 which comuines both pro- 

 cesses : a mould, usually of 

 plaster, fig. 8, a, is placed 



Fig. 7. 



on the disc of the throwing-wheel, b, and a thin 



Fig. 8. 



layer of the paste is pressed on to it, so as com- 

 pletely to take its form ; then to the guide-post, c, 

 is attached an arm, </, with a small brass plate, 



