EARTHS. 9 i 



ed with borax 4 and gum water, and by means of a volatile oilj applied 

 to the article ; it is then baked, and afterwards burnished. ' The 

 lustre ware is made by applying an oxide of gold,* with a volatile 

 oil, which is laid upon the vessels, colored by umber or red clay ; 

 this appears through the gold, and gives the copper tint. The 

 steel colored ware is covered with the precipitate by muriate of 

 ammonia, from the muriate of platinum, which is applied in a similar 

 way, but upon a cream colored basis ; and in both cases, it is 

 introduced into the enameller's oven, where the heat dissipates the 

 volatile principles, and the metals being left in their dull state, are 

 afterwards burnished. 



The ware is glazed before the gold and platinum are applied. 



When prints are made to adhere to the biscuit, in the manner al- 

 ready described, as the glaze is applied afterwards, it is important that 

 it should be transparent, that the colors may be seen through it. 



It should be mentioned that the glazing on the best porcelain, par- 

 ticularly that of China, is composed entirely of feldspar, finely pulver- 

 ized, and suspended in an aqueous fluid^ which is said to be in China,- 

 a lye of fern ashes ; no lead, or other metallic matter, enters into its 

 composition, and it requires a very great heat to produce its fusion ; 

 it is much harder than the glaze on most European porcelain. 



The Chinese ware is made so firm that it is merely dried before 

 dipping it into the glaze, and does not require a previous baking ta- 

 bling it to the state of biscuit. 



In general, the European porcelain, although superior to the Ori- 

 ental in whiteness and beauty, and in its exquisite ornaments, is in- 

 ferior in hardness, infusibility, weight, capability of enduring sudden 

 changes of temperature, and in the permanency of its glazing. Some 

 of the Saxon porcelain is said to be equal to the Chinese. 



Crucibles are made of the most infusible ckys, arid pipes and tiles 

 are manufactured upon similar principles with those that have been 

 explained. f 



Bricks, of every variety, are merely rude pottery. 



Fire Bricks are made of very refractory clay, called fire clay, and 

 are both more infusible and worse conductors of heat than common 

 bricks. They are sometimes prepared so as to be soft, or capable 

 of being cut, in order that they may be adapted to different purposes,- 

 and the fire, as they are used, hardens them afterwards 5 at other 

 times they are burned hard at first* Those manufactured at New 



* A private letter to the author from Mr. Accum, in 1809, mentioned, that fulmina-* 

 ting gold was applied in this way ; if so, doubtless its explosive character was de- 

 stroyed by the combustible matter of the oil of spike, with which it was said to be 



t See Parkes' Essays, Vol. II ; Gray's operative Chemist, and Bigelow's Tech- 

 nology. 



