tJie Substances employed in Pottery, 44- 1 



slightly transparent, and capable of standing a very strong and 

 sudden heat; it was produced by mixing soda to the extent ol' 3^ 

 per cent, in a 1 ittle clay prepared for the common white body, and 

 was then fired in the biscuit kiln. The clay employed having 

 been previously well dried, so as to weigh it without water, the 

 proportional quantity of soda requisite was then calculated and 

 weighed out ; the clay was again mixed with water along with 

 the soda ; it was then formed into capsules, which after being 

 fired and then broken, presented the appearance of a vitrified 

 or fused body. 



1. The common white ware or earthenware is made from 

 flint, Cornish stone, china clay, and blue clay, and does not 

 require such a high temperature in burning as the porcelain 

 does. By analysis of a piece of white ware manufactured in 

 this city, it was found to contain — 



Silica 68-55 



Alumina and protoxide of iron . 29'13 

 Lime 1-24 



98-92 

 Specific gravity 2*36 



Coloured ware is also manufactured from the same sub- 

 stances, but mixed with a colouring agent which stains the 

 body. 



2. The toqua or blue-coloured ware is coloured by cobalt. 



3. The sage or greenish- blue coloured ware, by nickel and 

 cobalt. 



4. The drab or buff-coloured ware by chromate of iron. 



5. The body for the cane or yellow-coloured ware is pro- 

 duced by a mixture of sandy clay and common red clay, the 

 same as used for red bricks, but is generally produced from 

 the natural yellow clay found in particular localities. 



6. The last-mentioned body is also employed for making 

 Rockingham ware, which only varies from the cane ware by 

 possessing a different glaze. 



7. The common black ware body is made from the red clay 

 alone. 



8. The Egyptian ware body is made from ironstone, ball 

 and red clay. 



These four last-mentioned bodies are not nearly so expen- 

 sive as the white ware, and do not require nearly such a high 

 temperature to burn them ; therefore they are, comparatively 

 speaking, soft bodies. 



9. Salt glazed wai'e 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 



