the Substances employed in Pottery. 



443 



materials in different proportions, and has a brilliant black 

 appearance. 



4. The glaze used for cane or yellow-coloured ware is made 

 from flint, red lead, and Cornish stone. 



5. The Egyptian ware owes its value to the beautiful and 

 rich tinted black glaze, made from flint, Cornish stone, red 

 lead, and manganese, with which it is covered. 



These four last-mentioned glazes are made by stirring the 

 substances together with a certain quantity of water, and pass- 

 ing it through a very fine sieve or search. Glazes do not re- 

 quire such a high temperature to fuse them on the surface of 

 the ware, as the body does to be burned. 



6. The glaze for salt glazed ware is common salt, which is 

 thrown in at the top of the kiln through a number of small 

 apertures in the crown of it, and diffuses itself through all 

 parts of the kiln, giving the ware the required glaze. The 

 action that is supposed to take place, when the salt is thrown 

 into the kiln, is owing to its decomposition. The chlorine of 

 the salt combines with the hydrogen of the water, which is 

 mechanically lodged in the salt, forms muriatic acid gas, which 

 passes off, while the sodium combining with the oxygen of the 

 water then unites with the silica in the ware, forming a sili- 

 cate of soda which fuses on its surface. The salt is not thrown 

 in until the kiln has been raised to its greatest necessary tem- 

 perature. 



Table of the Composition of Clays and Porcelain when free 

 from Water. 



Cornish china clay 



Cornish china clay 



Sandy clay 



Pipe clay 



Blue clay 



Red clay 



Fireclay 



Yellow clay 



English china ware, No. 1 ... 



No. 2... 



No. 2.., 



Berlin ware 



Superior Chinese ware 



Inferior Chinese ware 



Common English white ware 



53-16 

 5312 

 70-29 

 61-39 

 53-52 

 52-11 

 69-33 

 65-06 

 39-88 

 40-60 

 39-68 

 72-96 

 71-04 

 68-96 

 68-55 



45-61 



46-00 



27-47 



36-61 



43-89 



36-19 



23-62 



30-68 



21-48 



2415 



24-65 

 24-78 

 22-46 

 29-24 

 29-13 



-31 

 •31 

 1-33 

 1-54 

 1-20 

 8-17 

 5-56 

 3-70 



-41 



•57 



-90 



•46 



1-39 



1-56 



1-49 



-56 



10-06 



14-22 



14-18 



104 



3-82 



1-60 



1-24 



51 

 51 



Trace 

 Trace 

 Trace 

 2-04 

 Trace 

 Trace 

 Trace 

 43 

 31 

 Trace 

 Trace 

 Trace 

 Trace 





26-44 

 15-32 

 15-39 



2-14 



5-28 

 5-79 

 1-22 

 2-68 



2-558 



2-419 

 2-314 

 2-314 

 2-360 



