EARTHS. 289 



Handles, spouts, and other appendages are made separately, and 

 are stuck on afterwards, with a thin paste of the clay, called slip. 



Vessels that are to have a peculiar form, oval, scalloped, fluted, 

 &c. are made in moulds, usually of calcined plaster of Paris, 

 which, by its absorbing power, aids in drying the articles, and the 

 moisture is expelled from the moulds by heat, so that they are soon 

 rendered serviceable again. 



Burning or Baking. The vessels, after they are dried, either 

 in the air, or in stove rooms, are placed in earthen cases, called seg- 

 gars, and these are so arranged that one covers another, in the oven 

 or furnace, where they are gradually heated for about 12 hours, by 

 flues, communicating from without, and the full heat is maintained 

 from 24 to 48 hours ; more or less, according to the size of the es- 

 tablishment, and the nature of the ware.* The furnace being grad- 

 ually cooled, the pieces are withdrawn, and are then in the state 

 of biscuit, as it is called : it will be a perfect pottery, only it is ab- 

 sorbent of fluids, and therefore cannot be used, except for promoting 

 evaporation, when it is desired that the fluid should pass through the 

 pores and be exhaled from the outside. It adheres to the tongue, 

 because it absorbs its moisture. 



Porcelain contracts so much in baking, that some tablets which I 

 have from the Royal Manufactory at Sevres,f in France, which were 

 marked off into ten equal parts, are shrunk one division, comparing 

 them with those that have not been baked. 



Magnesia very much diminishes the shrinkage of the porcelain, and, 

 in the form of steatite, is now employed by the English manufacturers. 

 Great quantities of bones are consumed in the English potteries ; 

 it is done for economy, for the quality of the ware is injured, as to 

 firmness and weight, although it is white and translucent. 



Ornamenting. In the state of biscuit, the figures are usually put 

 on ; in the finer kinds, by the pencil, and in the most beautiful por- 

 celain, by the best artists, with exquisite taste and skill ; and often a 

 separate figure or scene is painted upon every piece of an extensive 

 set : the colors are metallic oxides. The ground oxide, in fine pow- 

 der, is intimately mixed with gum water, acid of tar, oil of turpentine, 

 or some other essential oil, and after the color is laid on, the fluid is 

 entirely evaporated. The colors employed are the same as those 

 mentioned under glass. 



* Trial pieces are withdrawn, from time to time, to enable the manufacturer to 

 judge of the state of the ware. 



t This is a part of a very instructive collection, containing a complete suite of all 

 the materials used in the manufacture of French porcelain, and in all their stages of 

 preparation and fabrication, from the decomposed granite, up to the perfect vessel ; em- 

 bracing also a series of colors, applied upon the porcelain, and accompanied by ex- 

 planatory and descriptive catalogues. It was presented to me by Mr. Alexander 

 Brongniart, the superintendant of the manufactory, a gentleman well known for his 

 valuable researches, and excellent works in mineralogy and geology. 



37 



