THE POTTERY INDUSTRY. 303 



Decoration. — Common earthenware is rarely decorated, but 

 stoneware for domestic use, if salt glazed, may sometimes be 

 decorated by tracing designs in the green clay and filling these in 

 with cobalt or other coloring matter. 



White earthenware and porcelain are often elaborately deco- 

 rated, either under or over the glaze. The form of decoration 

 most often seen is print work. This is done by printing a copper- 

 plate design on special paper, and applying this to the surface of 

 the ware. After being allowed to stand for a few hours the paper 

 is washed off, but the ink of the design is retained on the surface 

 of the ware. The colors are then fixed by firing in a muffle kiln 

 at a dull red heat. The print work is sometimes "filled in" and 

 elaborated by brush work, or on better grades of ware the entire 

 design may be hand painted. The more delicate colors as well as 

 gold have to be applied over the glaze as they are destroyed by 

 hard firing. With chromolithography a soft and ornamental 

 multicolored design can be produced at one operation, but it is 

 but little used in this country, although productive of beautiful 

 effects. 



Electrical porcelain, — This forms a separate branch of the clay- 

 working industry. These insulating materials are made of a 

 mixture of white-burning clays and molded by the dry-press 

 process. It is necessary to burn them' to vitrification, and none 

 are probably burned below cone 10 and some at cone 12. They 

 are usually glazed. 



Sanitary ware is made sometimes from the same classes of clay 

 as white earthenware, but the body is usually vitrified or nearly 

 so, and is glazed. The ware is formed by hand in plaster molds, 

 and great care has to be exercised in drying and burning. 



Bath tubs and washtubs. — These are commonly made from 

 buff-burning clays, such as fire clays and retort clays, and covered 

 with both a white slip and a. glaze. The lining is usually vitrified, 

 but not the body, and they are termed porcelain lined. The mold- 

 ing, drying and burning of such a large object as a bath tub re- 

 quires much care and time. The molding is done by hand in large 

 plaster molds. The wares are burned commonly at from cones 

 9 to 10, or perhaps slightly higher. A finished bath tub may 

 weigh as much as 1,100 pounds. 



