of good plasticity, free from grit and burn porous but steel-hard at cone 05-03.

Clays of this grade are not at all scarce and they occur widely distributed over the State. In the northern counties many of the Pleistocene and post-Pleistocene clays found in the valleys are of the proper quality for flowerpots, and other earthenware vessels. A number of small potteries are supplied from deposits around Linden, near Elizabeth, and some of the red-burning Raritan clays are also adapted to earthenware work. In the central part of the State, the Clay Marl beds I and II are locally sufficiently free from grit to be used, but the Cohansey and Cape May clays are not as a rule sufficiently fusible to burn dense at a low cone. The Alloway clays, however, in the southern part of the State might also be used with success.

Stoneware clays.-Those commonly employed are semirefractory clays burning to a nearly impervious body at cones 5 to 7, but fusing at about cone 27, although some, dug about Woodbridge and South Amboy, do not fuse lower than cone 33 and can be classed as refractory clays. They should possess good plasticity, and a tensile strength of not less than 150 pounds per square inch, although many of the New Jersey stoneware clays do not much exceed 100 pounds per square inch. Freedom from soluble salts which will form a scum on the green ware, and freedom from warping and cracking in burning are also essential characters. The clay should not shrink excessively in burning, and should be of a degree of refractoriness to vitrify at the temperature necessary to melt the glaze. Sulphur in any form is an undesirable ingredient. The better grades of stoneware are commonly made of a mixture of two or more clays.

The Raritan beds around South Amboy form the main source of stoneware clay in the State, and large quantities are shipped from there to potteries in neighboring states. Aside from these, few stoneware clays are found in any of the other formations except the Alloway clay. Some of the Pleistocene clays may be found suitable for stoneware manufacture, but they would be much less refractory than those of the Raritan formation. None of the Cohansey clays examined, if used alone burn dense enough

for stoneware manufacture. That from Loc. 207 (Toms River), might do for stoneware if mixed with a tighter burning clay.

Clays for white ware, porcelain and sanitary ware.-Two kinds of clay are used in the manufacture of these grades of ware, viz., kaolin and ball clay. No kaolin of suitable quality has ever been found in New Jersey, nor is there much chance of finding any— indeed, it is extremely doubtful whether any exists, the so-called "kaolin" of the Woodbridge district not being a kaolin at all but a micaceous sand.

Ball clay is found only in the Raritan formation especially near South River, and there is no likelihood of its being found in other formations in the State. Since the New Jersey ball clays show a tendency to crack in burning they cannot be used in large quantities in a pottery body. A ball clay should be plastic, burn white, and not warp or crack in drying or burning, and should burn steel-hard at cone 8 or lower.

The other raw materials used in white-ware bodies are ground flint and spar, but neither of these is found in commercial quantity in New Jersey, although veins of them may possibly occur in the Highland region. The crude materials are brought to Trenton in large quantities from other states and milled there.

The following table gives the composition of several American ball clays and kaolins, as well as of foreign clays, these latter being added for the purpose of comparison:

1, Edgar, Fla.; 2, Burt Creek, N. J.; 3, South Amboy, N. J.; 4, Mayfield, Ky.; 5 and 6, "Poole" clay from Wareham, England.

1, Brandywine Summit, Pa.; 2, Harris Clay Company, near Webster, N. C.; 3, West Cornwall, Conn.; 4, Glen Loch, Pa.; 5, Cornwall, England; 6, CoussacBonneval, France; 7, Zettlitz, Bohemia; 8, Pilsen, Bohemia.

MANUFACTURE OF POTTERY.

In making pottery there are certain steps that are common to all grades of ware, but the care of preparation, and the number of steps is increased in the manufacture of the higher grades. The different steps may be grouped as follows:

Clay is sometimes exposed to the weather as a preliminary means of preparation, but the custom is not a widespread one. High-grade clays are usually freed from grit and sand by a washing process (see Chap. I).

Tempering.

Chaser mills are sometimes used at stoneware factories, but none are in operation in New Jersey. They consist of a circular

iron pan in which there revolves a frame bearing 2 narrow iron wheels, 30 to 36 inches in diameter. As this frame revolves, the wheels by means of a gearing, travel from the centre to the circumference of the pan and then back. The clay and water are placed in the pan and the action of the wheels grinds and cuts it up, the tempering taking from one to two hours. The action of such a machine is quite thorough, but considerable power is required to operate it.

Pug mills.-The principle of these is similar to those used in brick manufacture (p. 225), but they differ in being upright or vertical. The clay and water are added at the top and slowly mixed, being at the same time forced down to the opening at the bottom of the box.

Tables.-Kneading tables are used at some factories for working the clay by machine instead of wedging it by hand. Although much used abroad, their introduction into this country has been rather restricted. The machine consists of a circular table about 6 feet in diameter, the upper surface of which slopes outward. On this are 2 conical rolls, 20 to 30 inches in diameter and about 8 inches wide. These rolls have corrugated rims, and are attached to opposite ends of a horizontal axis, having a slight vertical play. The clay is laid on the table and as the rolls travel around on it, the clay is spread out into a broad band. A second axle carries 2 other pairs of rolls of the same shape but smaller size, which travel around in a horizontal plane. These rolls press the band of clay together again. In this way the clay is subjected to alternating vertical and lateral pressure and all air spaces are thus closed. The rolls make 10 to 12 revolutions per minute, and the machine kneads 2 to 3 charges of 350 pounds per hour.

Molding.

After the clay has been properly tempered, the next step in the process of manufacture is molding. As indicated above this is done in four different ways, the clay having first been thoroughly kneaded, usually by hand, in order to insure its complete homogeneity and freedom from all air bubbles.

Turning. This is done on a rapidly revolving horizontal wheel, the potter taking a lump of clay and placing it on a rapidly revolving disk. Wetting the surface with a slip of clay and water, he gradually works the revolving mass into the desired form. After being shaped, the object is then detached from the wheel by running a thin wire underneath it, and it is set aside to dry. Crocks, jugs and similar articles are turned, this method being often employed for molding common stoneware, and sometimes for earthenware.

Jollying or jigging. This is a more rapid method than turning, and the clay to be used for this purpose is tempered to a much softer consistency. The jolly is a wheel fitted with a hollow head to receive the plaster mold, the interior of which is the same shape as the exterior of the object to be molded. A lump of clay is placed in the revolving mold and is gradually forced up around the sides of the latter. In the beginning of the operation this is done by the fingers, but finally a metallic arm or templet is used, which is brought down into the mold and serves to shape the interior of the object. Cups, crocks, jugs, pitchers and even wash basins can be molded in this manner. Articles with tapering necks are generally jollied in two parts, which are subsequently cemented together with slip, while handles are stamped out separately and afterwards fastened on the article.

A modification of jollying, used for making plates and saucers, consists in having a plaster mold, the surface of which has the same shape as the interior or upper surface of the plate to be formed. The potter's assistant takes a piece of clay of the desired size, and pounds it to a flat cake, called a "bat," which is laid on the mold; he then shapes the other side or bottom of the plate by pressing a wooden templet of the proper profile against it as it revolves. A modification of this machine is one used for flower pots, in which the mold is of steel, and instead of a templet, a solid piece, also of metal, and fitting the interior surface of the pot, is brought down into the mold.

Pressing.-Ewers and vessels of oval or elliptical section are usually made by means of sectional molds, consisting of two or three pieces, the inner surface of which conforms to the outer