178 Mn. CourER on the Chemical Composition of Potter)'. 



(8.) The Egyptian ware body is made from ironstone, stiff clay, man- 

 ganese, and red clay. 



These four lust-mentioned bodios do not require nearly such a high tem- 

 porature to ban them; therefore, they are, comparatively speaking, soft 

 bodies. 



(9.) Salt glazed ware is made from sandy clay, and a little sand to 

 keep the body open, or make it less compact ; but for large salt glazed 

 ware, potsherd, which is ware that has been fired and then ground, is 

 employed to render the body still more open or porous, and also to give it 

 a greater capability of standing sudden heats or colds. This ware is much 

 used in public works for chemical purposes ; it is exposed to the action of 

 the flame during burning, whereas other kinds of ware are protected by 

 saggars from the flames. 



VII. The glaze vitrifies the surface of the body, rendering it generally 

 capable of withstanding acids. It is a very important point with the 

 manufacturer to obtain a glaze which will adhere to the body without 

 crazing or peeling off, as he may discover a good body, but not find a 

 glaze to answer it, since every glaze will not adhere to the same body ; 

 and hence every manufacturer has a glaze of his own composition. 



(1.) The substances used in the preparation of the glaze for the white 

 ware are — borax, China clay, flint, Cornish stone, Paris white, and 

 white lead. In preparing the glaze, a substance technically termed frett, 

 is first made, consisting of borax, China clay, flint, Cornish stone, and 

 Paris white, which are fused together in a kiln, and, when ready, allowed 

 to flow into water, which shortens it, owing to the water being mechani- 

 cally lodged in it and keeps it from adhering to the bottom of the vessel, 

 rendering it much easier to pound. Frett is a beautiful glass, coloured 

 by a little iron, and is pounded, and water ground along with Cornish 

 stone, flint, and white lead. This constitutes the glaze for white ware. 



Analysis of of F tt 



white glaze. uiureu. 



Silica, 43-66 55*98 



Lime, *52 2*52 



Alumina and protoxide of iron,.... 9*56 10*38 



Borax, 2008 3112 



Carbonate of lime, 10*88 — 



Carbonate of lead, 15*19 — 



99*89 100* 



Specific gravity, 2*345 



A piece of earthenware was brought lately from Wisconsin territory, 

 N. America, having been discovered several feet under ground, the glaze of 

 which was tested and found to be composed of silica, iron, alumina, lime, 

 sulphate of lime, and antimony, which was a beautiful rich white glass, 

 concealing a common red clay body. 



(2.) The glaze of Rockingham ware possesses a beautiful brownish 



