Diggers in the Earth

by Eva March Tappan

Clay is a kind of earth containing mostly alumina and silica or sand, that can be mixed with water, moulded into any shape, retain that shape after it is dry, and become hard by being burned. If you want to make a china cup, you must have a fine sort of clay called "kaolin," which is pure white when it is fired and is not very common; but if you want to make bricks, it will not be at all difficult to find a suitable clay bank. And yet the clay, even for bricks, must be of the right kind. If it contains too much silica (sand), the brick will not mould well; if too much alumina it will be weak; if too much iron, it will lose its shape in burning; if too much lime, it will be flesh-colored when it is burned.

If you want to find out whether a building-brick is of good quality, there are some tests that a boy or girl can apply as well as any one. First, look the brick over and note whether it is straight and true, and whether the edges and corners are sharp. Strike it, and see whether it gives a clear, ringing sound. Then weigh it and soak it in water for twenty-four hours. Weigh it again, and if it is more than one fifth heavier than it was before soaking, it is not of the first quality.

After the clay has been dug, it must be "tempered," that is, mixed with water and about one third or one fourth as much sand as clay, and left overnight in a "soak pit," a square pit about five feet deep. In the morning the workmen shovel the mass over and feed it into the machines for forming the bricks. The mixing is better done, however, in a "ring pit." This is a circular pit twenty-five or thirty feet in diameter, three feet deep, and lined with boards or brick. A big iron wheel works from the center to the edge and back again for several hours, through and through the clay. A method even better than this is to put the clay and sand and water into a great trough, in which there is a long shaft bristling with knives. The shaft revolves, mixes the clay, and pushes it along to the end of the trough. This is called "pugging," and the whole thing—trough, shaft, and knives—is a "pug mill."

In the old days bricks were always made by hand. The moulder stood in front of a wet table whereon lay a heap of soft clay. He either wet or sanded his mould to keep it from sticking. Meanwhile, his assistant had cut a piece of clay and rolled it and patted it into the shape of the mould. In making bricks, there can be no patching; the mould must be filled at one stroke, or else there will be folds in the brick. To make a good brick, the moulder lifts the clay up above his head and throws it into the mould with all his force. Then he presses it into the corners with his thumbs, scrapes off with a strip of wood any extra clay, or cuts it off with a wire, smooths the surface of the brick, puts mould and brick upon a board, jerks the mould up and proceeds to make another brick.

IN A NEW JERSEY BRICK MILL
Copyright by Underwood and Underwood.
This man is moulding a fire-brick to its final shape.

No matter how expert a moulder may be, brick-making by hand is slow work, and in most places machines are used. In what is called the "soft-mud" process, the clay is pushed on by the pug mill to the end of the trough. There stands a mould for six bricks. A plunger forces the clay into it, the mould is emptied, and in a single hour five thousand bricks can be made. By what is called the "stiff-mud" process, the stiff clay is put into a machine with an opening the size of the end or side of a brick. The machine forces the clay through this opening, cuts it off at the proper moment; and so makes bricks by the thousand without either mould or moulder. A third way of making brick is by what is called the "dry process." The clay is pulverized and filled into moulds the length and breadth of a brick, but much deeper, and with neither top nor bottom. One plunger from above and another from below strike the clay in the mould with much force, and make the fine, smooth brick known as "pressed brick." All this is done by machinery, and some machines make six bricks at a time. These "dry" bricks are fragile before they are burned, and must be handled with great care.

Bricks cannot be put into the kiln while they are still wet, for when a brick is drying, it is a delicate article. It objects to being too hot or too cold, and it will not stand showers or drafts. In some way about a pound of water must be dried out of each brick; but if you try to hurry the drying, the brick turns sulky, refuses to have anything more to do with you, and proceeds to crack. To dry, bricks are sometimes spread on floors; or piled up in racks on short pieces of board called "pallets"; and sometimes they are put upon little cars and run slowly through heated tunnels. The last is the best way for people who are in a hurry, for it takes only from twenty-four to thirty-six hours to make the bricks ready to go to the kiln to be burned.