5. In preparing the clay for use, the potter adds to it, when necessary, a portion of fine loam, in order to lessen its tenacity, and to prevent the vessels to be made of it from cracking, while undergoing the fire. When the materials have been mixed, and partially incorporated with water, the mass is thrown into a tub, fixed in the ground about one-half of its depth. In the centre of this tub, is placed a shaft, in a perpendicular position, from which radiate, in a horizontal direction, a number of knives or cutters.
6. This machine is put in motion by horse-power, and by it the clay is repeatedly cut, and properly kneaded. The workman then cuts it into thin slices with a small wire, and, having rejected all matters not fit for his purpose, he further kneads it with his hands, and forms it into lumps, corresponding in amount of matter with the different vessels which he proposes to make.
7. For the best kinds of this ware, the same species of clay is used; but then it is differently prepared. It is first dissolved in water; and, when the coarser particles have settled to the bottom of the vessel, the fluid suspending the rest is drawn off, and made to pass through a sieve into a reservoir. After the particles of the material have precipitated, the water is drawn off, and the residuum is thrown upon a large flat pan or reservoir made of bricks, where the mass is freed from its superfluous moisture by evaporation in the air, or by means of artificial heat applied beneath. It is then laid by in a damp place, for future use.
8. Before the clay, thus purified from extraneous and coarser particles, is formed into vessels, it is beaten with a stout piece of wood, until the mass has become of an equal consistence throughout, and then repeatedly cut into two pieces with a wire, and slapped together to expel the air. The former of these operations is called wedging, and the latter, slapping.
9. White and cream-colored wares are made of clays which contain so little oxyde of iron, that it does not turn red in burning, but, on the contrary, improves in whiteness in the furnace. There are several species of white clay, found in many different localities, most of which, however, are known under the denomination of pipe-clay; or they are distinguished by the names of the places where they are obtained.
10. In preparing these clays for use, they are reduced to a minute division by machinery, and afterwards dissolved in water, and otherwise treated in a manner similar to that used for the better kinds of common wares, as described in the seventh and eighth paragraphs. For the purpose of diminishing the shrinkage in the fire, and with the view of increasing the whiteness of the ware, pulverized flint-stone is added to the clay, in the proportion of about one part of the former to five of the latter.
11. In reducing the silex to the requisite fineness, it is first brought to a red heat; and, while in this state, it is thrown into cold water, to diminish the cohesion of its parts. It is then pounded by machinery, levigated with water in a mill, sifted, mashed, and otherwise treated like the clay. The materials are mixed while in a state of thin pulp.
12. The several operations performed by the potter, in converting the clay thus prepared into different kinds of vessels, and in completing the whole process of the manufacture of earthen ware, may be included under the following divisions, viz., throwing, turning, pressing, burning, painting and printing, and glazing. They are not, however, all used in producing and finishing vessels of every shape and quality.
13. Throwing.—This operation is performed on a potter's wheel, which consists of a round table, and some simple means to put it in motion. The clay having been placed on the centre of this machine, the workman communicates to the latter a rotary motion with his foot, and gives the proposed form to the material with his hands, which have been previously wet with water, to prevent them from sticking. This method is used for all vessels and parts of vessels of a circular form; and, in many cases, no other operation is necessary to give them the requisite finish, so far as their conformation is concerned.
14. Turning.—The vessels are cut from the thrower's wheel with a small wire; and when, by the evaporation of moisture, they have become firm enough to endure the operation, they are turned on a lathe. The objects of this operation are to communicate to them a more exact shape, and to render them more uniform in thickness. The potter's wheel, with the addition of some contrivance to hold the pieces in a proper position, is frequently used for turning. The coarser kinds of common wares are never turned.