616 



POTTERY 



taken, before putting them into their saggers, to remove the glaze-powder from their 

 bottom parts, to prevent their adhesion to the fire-clay vessel. 



Mortar Body, is a paste composed of 6 parts of clay, 3 of felspar, 2 of silex, and 

 1 of china-clay. 



Ironstone-Ckina. Some of the English porcelain has been called ironstone-china. 

 This is composed usually of 60 parts of Cornish stone, 40 of china-clay, and 2 of flint- 

 glass ; or 42 of felspar, the same quantity of clay, 10 parts of flints ground, and 8 of 

 flint-glass. Slag from iron-smelting is sometimes introduced into the paste. 



The glaze for the first composition is made with 20 parts of felspar, 15 of flints, 6 

 of red lead, and 5 of soda, which are fritted together ; with 44 parts of the frit, 22 

 parts of flint-glass, and 15 parts of white lead, are ground. 



The glaze for the second composition is formed of 8 parts of flint-glass, 36 of 

 felspar, 40 of white lead, and 20 of silex (ground flints). 



The English manufacturers employ three sorts of compositions for the porcelain 

 biscuit : namely, two compositions not fritted ; one of them for the ordinary table 

 service ; another for the dessert, service, and tea dishes; the third, which is fritted, 

 corresponds to the paste used in France for sculpture ; and with it all delicate kinds 

 of ornaments are made. 



The glaze for the first two of the preceding compositions consists of, felspar 45, 

 flints 9, borax 21, flint-glass 20, nickel 4. After fritting that mixture, add 12 parts 

 of red lead. For the third composition, which is the most fusible, the glaze must 

 receive 12 parts of ground flints, instead of 9 ; and there should be only 15 parts of 

 borax, instead of 21. 



Description of the Porcelain Mill. 



1. The following figures of a felspar and flint mill (figs. 1650, 1651) are taken from 

 plans of apparatus constructed by Mr. Hall, of Dartford, and erected by him in the 

 Royal Manufactory of Sevres. There are two similar sets of apparatus, which may 

 bo employed together or in succession ; composed each of an elevated tub A, and of 



three successive vats of reception A , and two "behind it, whose top edges are upon a 

 lower level than the bottom of the casks A, A, to allow of the liquid running out ot 

 them with a sufficient slope. A proper charge of kaolin is first put into the cask A, 

 then water is gradually run into it by the gutter adapted to the stopcock , after 

 which the mixture is agitated powerfully in every direction by hand with the stirring- 

 bar, which is hung within a hole in the ceiling, and has at its upper end a small tin- 

 plate funnel to prevent dirt or rust from dropping down into the clay. The stirrer 

 may be raised or lowered so as to touch any part of the cask. The semi-fluid mass is 

 left to settle for a few minutes, and then the finer argillaceous pap is run off by the 

 stopcock a', placed a little above the gritty deposit, into the zinc-pipe which conveys it 



