PORCELAIN AND THE ART OF ITS PRODUCTION. 311 



whether by Louis Poterat or by Reverend, at Paris or Rouen, is dis- 

 puted. This ware has no relation with real porcelain ; it contains 

 neither kaolin nor feldspar, but is an artificial product, a kind of glass 

 made from a mixture composed essentially of sand, lime, potash, soda, 

 and a small quantity of marine marl. This mixture, made plastic by 

 the addition of manganese or other fluxes, is baked without glazing, and 

 is covered after baking with a glazing composed of silica, lead, potash, 

 and soda. The beauty of the material, its perfect glaze, and the 

 facility with which verifiable colors are fixed in it, make of tender 

 porcelain a ware exceptionally adapted to decoration. 



The discovery of tender porcelain did not arrest the investigations 

 of men of science and potters, who saw very well that it had none of 

 the characters of the porcelain of China. A bed of kaolin was found 

 in Saxony in 1709, and Bbttger set up at Meissen the first European 

 factory of hard porcelain. Fifty years later, in 1758, Guettard at 

 Alencon, and afterward, in 1769, Madame Darnet at Saint-Yeux, near 

 Limoges, discovered the French beds, and the industrial fabrication of 

 hard porcelain was begun in France in 1774. Tender porcelain gave 

 way quickly in the rivalry with hard porcelain. This was unfortunate, 

 in an artistic point of view, for the latter material is very unaccommo- 

 dating to the decorator. A more important object was, however, to 

 create for domestic economy an absolutely healthful industry, and 

 much is due to the illustrious Brongniart for having by his investiga- 

 tions put the manufacture of kaolinic porcelain on a firm scientific 

 foundation. 



Natural kaolin is never a pure clay, but contains also sand, unde- 

 composed feldspar, etc., in variable quantities, and must first be purified. 

 For this purpose the mass is pounded, and the products are separated 

 one after another by successive levigations with water. The clay, 

 which is extremely slow in settling, is drawn off first, and may be ob- 

 tained almost pure ; the other deposits, composed of more or less f eld- 

 spathic sands, are brayed in mills, and are destined to enter in their 

 turn into the preparation of the pastes. The nature of porcelain, its 

 physical and chemical properties, vary infinitely according to the pro- 

 portion of its two consituent elements (kaolin and feldspar), and as other 

 substances, lime, silicious sands, potsherds, etc., are added, as is often 

 done. Every country and every factory has its composition, which is 

 adapted to the use to which the porcelain is destined, to the degree of 

 resistance that is to be demanded of it, and to the kind of decoration 

 it is lo receive. Generally, porcelain is more solid as the proportion of 

 clay increases, and requires a higher temperature in baking ; if, on the 

 other hand, the proportion of feldspar is increased, it becomes more fu- 

 sible, may be baked at a lower temperature, and submits more readily 

 to decoration, but its plasticity and the possibility of working it easily 

 diminish rapidly^ The mixture of the materials should be perfect ; 

 when this is the case, the mass will keep for a long time, and become 



