BRICK. The earliest examples of this branch of the ceramic art were doubtless the sun-dried bricks of Egypt, Assyria, and Babylonia. Remarkable to say, many of these, which, in a northern climate, the frosts of a single winter would destroy, bare been preserved for some 3000 years by the dry, warm atmosphere of those countries. Sun baked bricks of ancient date are also found in the mud walls of old towns in India. Kiln-baked bricks must have been the products of a later time; but they are found in all the chief ruins of ancient Babylonia, where they were often used to face or bind together walls of sun-dried bricks, and occasionally they were even ornamented with enameled colors. Burnt bricks were employed in the foundations of the tower of Babel (Gen. xi. 3). These ancient bricks, whether baked by the sun or by fire, were all made of clay mixed with grass or straw. The ancient Greeks, probably owing to their pos sessing plenty of stone, cared little for building with burned clay; but most of the great ruins in Rome are built of brick, and the Romans appear to have introduced the art into England. Interesting historical information has been obtained from the impressions cm Roman and especially on Babylonian bricks. In many instances, the Roman bricks found in England have been removed from their original position, and employed in the construction of buildings of later date. The earliest instance in which bricks of the mod ern or Flemish make occur in England, is Little Wenham hall, in Suffolk, 1260.
Manufacture of Bricks.—Clay suitable for the manufacture of common bricks is an abundant substance, but there is a great difference in the nature and quality of the clays found in various localities. The TiMis of .clity`consistsf Of hydrattcd .$ificate of alumina, with a varying proportion of other mineral matters, chiefly free silica (sand), iron, lime, magnesia, and potash. Great advantage is derived from digging clay in autumn, and exposing it all winter to the disintegrating action of frost. This is not always attended to, but when neglected, the bricks made from it are apt to be unsound, and faulty in shape. The next process is that of tempering or mixing the clay into a homogeneous paste, which is sometimes done by the spade, but more commonly iu the pug-mill (see article Pottery) or by crushing between a pair of rollers; often, indeed, both are em ployed. In making bricks by the old hand process, the shape is given by a mold either entirely of wood, or of wood faced with metal, and without top or bottom. This admits of the clay being pressed into it by a tool called a plane, which is also used to produce an even surface on the upper and lower beds of the brick, off the superfluous clay. Sand is used to part the wet clay from the mold and the table on
which it rests.
Although hand-made bricks are still very common, yet machinery is now always employed when large quantities are required. Brick-making machines are of two lead ing kinds; one class of them being constructed to work the clay in a wet plastic state, the other class requiring it to be in a semi-dry condition. Of the two sorts, the wet clay machines are the simpler, cheaper, and can be worked by less-skilled workmen. On the other hand, the dry-clay machines, which make the bricks by forcing the clay into molds by strong pressure, shorten the process, as no time is required for drying them. The bricks so made, too, are not only of a more perfect shape, but they can be molded into any form, and may even be made highly ornamental at a very slight addi tional cost.
As might be expected, both the dry and the wet-clay machines of different makers vary considerably iu twir details. The general plan on which most of the wet-clay machines work is as follows: The machine is driven by steam, and the clay is fed by a hopper into a pug-inill, on the central shaft of which strong pugging blades are placed in a spiral manner. These prepare and force the clay out at the bottom, whence it passes over the carrying rollers to the pressing rollers, which force it through a die in a rectangular stream, so exactly shaped to the required size that nothing more is necessary than to cut it into single bricks by wires. These are set in a rocking frame, which can be so adjusted as to cut the bricks on the square or at an angle; the one plan being adopted when the clay is at rest, the other while it is in motion. When double-ended, the clay is forced out at opposite sides of the pugging cylinder, and there is then, of course, a cutting-table at either side, instead of only one. Some of these machines are provided with a pair of powerful crushing rollers, which reduce any hard lumps or stones before the clay enters the pug-mill. One of the best known wet-clay machines is that made by Clayton, Son & Co., London. When of a size which can be worked by a steam engine of 16-horse power, it produces from 20,000 to 30,000 bricks per day, and its price in 1871 was £330. Drain tiles are made by the same kind of machinery, with a peculiarly constructed die, so as to make clay into a hollow tube; so also are hollow bricks, with again an alteration in the shape of the die. Hollow bricks, having less body than those which are solid, are more easily and usually more thoroughly fired. On account of this, as well as by 'reason of their admitting of a current of air through them, they form, as a rule, dryer walls.