644 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



Mr. Johnson presented a number of drawings for the purpose 

 of explaining the composition of the different kinds of clay used 

 in the manufacture of pottery. He stated that he was disap- 

 pointed at the absence of Mr. Davis, who, he expected, would 

 have been present to give his views on this subject. He gave 

 an analysis of the Cornish stone, which he stated w^as composed 

 of quartz and felspar mixed. China clay is composed of silica, 

 alumina, protoxide of iron, lime, magnesia, water and alkali. 

 English China glaze is composed of Cornish stone, calcined flints 

 Carbonate of lime, Cornish clay, soda, borax, and white lead. 

 These are fritted together with 20 per cent of white lead and 10 

 per cent of flint. Black Etruscan vases are composed of silica, 

 alumina, oxide of iron and manganese, carbonate of lime, car- 

 bonate of magnesia, carbon and water. Greek vases are com- 

 posed of silica, alumina, oxide of iron, 'lime and magnesia. The 

 common stone ware is manufactured from the clay as found, and 

 sometimes with the addition of sand and broken stone ware. 

 Other diagrams which he exhibited showed tables of the compo- 

 sition of claj's and porcelain ware free from water, and of differ- 

 ent kinds of colored ware ; also, of the composition of hard and 

 eoft china. 



The Chairman stated that all clays contained a metal, and that 

 that metal had a great deal to do with making clay hold oil, 

 water, &c. 



Mr. Rouse, of New Jersey, said about two-thirds of the clay 

 used in the manufacture of pottery in this country is Jersey clay. 

 We get clay from Connecticut, Georgia, and other States. Clay 

 can be furnished us as cheap from Europe as it can from Georgia. 

 The manufacturing of the material is more expensive than the 

 material itself. If we make $60,000 worth of goods $30,000 of 

 it would be for labor. All potteries have failed in this country 

 until within these six years past. There are seven manufactories 

 at present in Trenton. We get the flint and borax duty free. 

 We import the English flint prepared at a cost of less than one 

 cent a pound. We also use felspar. The only difliculty we labor 

 under is the iron that is found in every clay, to extract which is 

 nearly impossible. 



Chairman. — Do you know what it costs to break the rock flint 

 and reduce it to the form in which it is imported. 



