classification

CLASSIFICATION OF CERAMICS

The old classification of Brogniart divides all ceramic products into three main classes and nine subdivisions, as follows:

FIRST CLASS.

Bodies sufficiently soft to be scratched with a knife, of a sandy-argillaceous character or containing lime and fusible in the heat of the porcelain kiln.

First Division.

Bodies soft burned, with a dull unglazed surface. Examples: Brick, building terra-cotta, drain tile, etc.

Second Division.

With the faint luster of an alkali earthy-silicate, the gloss produced by polishing or by incipient fusion. Example: Antique vessels.

Third Division.

A body similar to that of the first or second, but with a transparent lead glaze. Example: Common pottery ware.

Fourth Division. 

Ware enameled with nontransparent glazes containing tin oxide. Examples: Tile for porcelain stoves, and common dishes.

SECOND CLASS. 

Bodies which are hard, nontransparent, and of a siliceous-argillaceous mass that cannot be scratched with a knife, and are infusible.

Fifth Division. 

White bodies with a transparent lead glaze. Examples: Fine faience and dish-ware.

Sixth Division. 

A colored body with an earthy alkaline silicate glaze, and/or sufficiently dense to require no glaze. Example: Stoneware.

THIRD CLASS.

Bodies hard, translucent, also high in alkali, siliceous-argillaceous, softening in the hardest fire.

Seventh Division. 

Kaolinitic body with a glaze but mainly feldspathic. Example: True hard porcelain.

Eighth Division. 

Body of kaolin, plastic clay, and bone ash, with a lead-boracic-acid glaze. Example:
English soft porcelain.

Ninth Division.

Body of a glass-frit with addition of clay and a lead glaze. Example: French soft porcelain. In addition to the manufactures innumerated by Brogniart in his first division, flooring tile would belong in this category. It is now, however, customary to burn these, as well as the better grades of building terra-cottas, so hard that they are not to be scratched with a knife ; enabling them to better resist wear and the disintegrating action of the elements. Our common "red ware" corresponds exactly to that of the third division.

(Classification of clay is of service particularly to the chemist, in order to emphasize characteristics that are of moment to the potter. It is therefore be most practical to take as simple a classification as possible, and merely enumerate the chief technical characteristics without classifying all their possible combinations).

Clay chemical analysis