204 ON THS CHINA-STONE AND CHINA-CLAYS OF CORNWALL. 



Of this frit, when ground, 26 parts are taken, and added to, or mixed 

 with, — ■ 



26 of ground China-stone, 

 31 „ white lead, 

 7 „ Flint, 



7 „ Carbonate of Lime, &c, 

 3 „ Oxide of Tin, 



in which the biscuit is dipped prior to the last application of heat. The 

 colours to be laid on the ware are applied and burnt in prior to the for- 

 mation of the glaze, an article often requiring a separate burning for 

 each different colour, thus, especially in gilded articles, entailing an 

 additional amount of cost and labour. 



The China-stone increases the strength and sonorosity of the article, 

 while the ground Hint gives whiteness and density to the base of plastic 

 clay : earths are by themselves infusible, but on the addition of silex or 

 silica, another name for quartz, we form a silicate, to which, if we add 

 a third of earth, with an alkaline base, we form a body vitrifiable and 

 uniformly translucent. 



I shall briefly describe the mode in which the China-stone and China- 

 clay are treated, prior to their being turned, twisted, and flattened, to 

 form the numberless articles in which they greet the eye. 



The China-stone is ground to a fine powder by means of a number 

 of stones which are kept rotating on the bottom of a paved vat, when 

 it, as well as the clay and ground flint, are mixed with a certain 

 quantity of water, by a process termed " blunging," till of the consistence 

 of cream, when it is passed in a state of slop or slip through a series of 

 cambiic or lawn sieves kept rapidly revolving by a water-wheel, each 

 pint of the clay slip weighing twenty-four ounces, while that of the flint 

 or China-stone weighs thirty -two ounces. It is then passed through a 

 very fine silk sieve, after which these ingredients are mixed together in 

 variable proportions in a large vat or tub, and as soon as the mixture 

 has attained its requisite consistence, the water is driven off by evapora- 

 tion, which causing the slip to contain in its interstices an innumerable 

 quantity of air globules, renders it necessary that it should be sub- 

 mitted to the process of kneading or beating, after which it was for- 

 merly thought necessary, though now abandoned, that this "mass should 

 lie fallow for three or four months, when it is considered to be fit for 

 the lathe. 



The proportions of the ingredients used in the different kinds of 

 earthenware are as follow : — 



In cream colour or painted ware, — Dorsetshire clay, 56 parts ; kaolin 

 or China-clay, 27; flint, 14 : and China-stone, 3 parts. 



In brown ware, — red clay, 83 ; Dorset clay, 13 ; flint, 2 ; and man- 

 ganese, 2 parts. 



