BRICK, a kind of artificial stone made of baked clay. The usual form of a brick is a parallelopipedon, about 9 inches long, 4i inches, broad, and 3 inches thick. The art of brickmaking dates from very early times. We read that burnt brick was used in building the tower of Babel. The walls and various other buildings of ancient Babylon were made of burnt brick; several varieties of brick figure in Assyrian art, and most of the Assyrian literature was in the form of minute characters in baked clay (see BABYLON, BABYLONIA).
FlG- 1-Egyptian Brickmakers.
Brickmaking formed the chief occupation of the Israelites during their degrading bondage in Egypt. The bricks were made of clay mixed with chopped straw, and were probably sun dried. We read (2 Sam. xii. 31) that David made the children of Amnion pass through the brick kiln; and while the meaning of the statement is doubtful, it is thought that the in-struments mentioned in the context may have been used in preparation of the clay. Pliny informs us of three different kinds of bricks made by the Greeks. In Italy we have abundant evidence that the Romans used bricks largely; and it was they, probably, who introduced brickmaking into England. By the time of Henry VIII. the art had reached great perfection; and many fine brick buildings (e.g., the older part of Hampton Court) are extant from that period. Previous to the great fire of 1666, many of the London houses consisted chiefly of timber framework, filled in with lath and plaster; but after the fire, brick was used almost exclusively in building. Much of the brickwork remaining from that time is finely carved with the chisel. From the latter part of last century (1784) till 1850, bricks in this country were subject to taxation. In Holland, where stone is scarce, bricks have been in use from a very early period, both for domestic and public buildings.
The quality of bricks depends primarily on the choice of earths. There are three principal classes of brick-earths:(1.) Pure clays, consisting chiefly of alumina and silica, in various proportions, and with' a small percentage of other salts, iron, lime, magnesia, etc.; (2.) Loams or sandy clays ; (3.) Marls, or earths with a considerable proportion of lime. A paste of pure clay alone (made with water), while it may be easily moulded, will shrink and crack in drying and firing, in proportion to the excess of alumina over silica; but this can be remedied by mixture with a milder earth or with sand. Loams, again, are often so loose that they require the addition of lime as a flux. The London brickmakers add lime and ashes, or breeze, to their loams and marls, both as a flux and to prevent shrinking; such admixtures also, as will be seen, affect colour. Brick-earths are very various in composition. The proportion of ingredients in a good earth will be something like the following :silica, three-fifths; alumina, one-fifth ; iron, lime, magnesia, manganese, soda, and potash forming the other one-fifth. The clays of which fire-bricks for furnaces are made are almost entirely free from lime, magnesia, and like substances, which act as fluxes; they are found throughout the coal measures, immediately beneath the coal. The best, that of Stourbridge, will bear the most intense heat that can be produced, without fusion. The Welsh fire-bricks, and those of Windsor, Newcastle, and Glasgow, are other well-known varieties. The Dinas fire-brick consists almost entirely of silica ; to this is added about one per cent, of lime, and the mixture, after moulding, is intensely heated. In Austria, a very refractory siliceous brick is manufactured by M. Khern, the chief ingredient being quartz of the highest possible degree of purity.
The colour of bricks is determined by the proportion of hydrated oxide of iron and other ingredients they contain, also by the degree of heat in burning. Where iron is present without lime or such substances, a moderate red heat makes the bricks red, the intensity varying with the proportion of iron ; with more intense heat, the bricks, if slightly fusible, may be vitrified externally, and become greenish blue (e.g., the blue bricks of Staffordshire). The presence of lime changes the red colour produced by iron to a cream brown , magnesia also arrests the development of red. Clays burning a pale red will burn yellow if mixed
with a fusible white sand, such as is often found on heaths. Some clays, as those of Devonshire and Dorsetshire, burn of a clear white. The London malms give a rich brimstone yellow. The art of ornamental polychrome brick-work has of late years been much developed, especially by the German architects. The principal varieties of common bricks made in England are place bricks, grey and red stocks, marl facing bricks, and cutting bricks. The first two are used in ordinary walling. The marl facing bricks, made in the neighbourhood of London, are superior to the stocks, and used in the outsides of buildings. Cutting bricks, which are the finest kind of marl and red bricks, are used in arches over windows and doors.
The process of brickmaking varies considerably in different localities. In the following account we shall, in the first instance, confine our attention to methods adopted in the vicinity of London, and thereafter note some of the peculiarities of other systems. The most common mode of preparing the clay, in the London district, is that of maiming. Among the varieties of brick-earth found there malm is a substance that can be used for bricks without any addition. But it is now rare, and an artificial malm is made by mixing chalk and clay, previously reduced to pulp, and allowing the mixture to consolidate by evapora-tion. Bricks of the best quality are made with this alone; but for the commoner sorts some of the malm is added to the clay or loam, sufficient to make it fit for brick-making.
The earth is dug up in autumn, and placed on a level floor, banked round in order to retain the malm in the process of malming. Exposed during the winter, it is more or less broken up and pulverized by the frost, &c. The machinery for maiming consists of two washing-mills, viz., the chalk and clay mills, which are placed together, not far from the brick-earth. The chalk-mill is a circular trough in which chalk is ground in water, by two heavy wheels with spiked tires, drawn round by horses. The pulp thus made passes by a shoot into the clay-mill, another and a larger circular trough, where it gets mixed with clay that is being cut and stirred in water by knives and harrows, also put in motion by horses. The creamy liquid malm passes through a grating into shoots which convey it to the brick-earth, over which it is distributed as equally as pos-sible. It is now left to settle for a month or more, the water being drained off at intervals, till the mass is firm enough to bear a man walking over it. A thin layer of ashes, about 3 inches for every spit of earth, is spread over the surface (this process being technically called soiling), and the whole is now ready for the moulding season, which commences generally in April.
The mass of earth, malm, and ashes is first tempered, or thoroughly turned over and mixed with the spade, while water is added to give it the proper consistence. The tempered clay is then conveyed to the pug-mill,a conical tub, in which revolves (driven by horses) a vertical shaft with horizontal knives so inclined that the clay is slowly forced down to the narrow end by their motion. Several of these knife-arms are furnished with cross knives, which assist in the cutting and kneading process. The clay comes out laterally at the bottom as a uniform mass, and is ready for moulding.
The moulder stands at a table or stool, on which are placed some of the tempered clay in front of him, a little dry sand to the right and left, a small tub of water with the strike in it, a brick-mould, and a stock-board. Back-wards from the stool extends the page, a pair of iron rails, on wood, on which the raw bricks are pushed away by the moulder. The brick-mould is a rectangular case of sheet-iron, without top or bottom, having the two longer sides strengthened with wood. The stock-board, supported on four pins in the moulder's stool, fits easily into the mould; it has often a solid elevation in the middle, for producing a hollow in the brick. The moulder receives from the clot-moulder (usually a woman), standing on his right, a piece of clay somewhat larger than a brick. Having sprinkled sand on the stock-board, and dashed the mould, after mois-tening it, in the left sand heap, he places the mould on the stock-board, and dashes the clay into it with force, then pressing it with his fingers so as to fill the angles. With the strike (a short, smooth piece of wood) he strikes off the surplus clay; then he turns the brick out of the mould on a thin board or pallet, rather larger than the brick, and slides it along the page to the taking-off boy, who stands ready to put the bricks on a barrow of special construction ; on this, after sprinkling with sand, they are conveyed to the hack ground. The bricks are each carefully removed from the barrow between two pallets, and built up in hacks, about eight bricks high, and two in width (placed edgewise, and in an angular direction,the hacks being about 11 feet apart, from centre to centre. They are covered with straw or reeds at night or in bad weather. When half dry the bricks are separated somewhat (scintled), to allow free access of the air. The time taken in drying varies from three to six weeks. Burning. In the vicinity of London bricks are commonly burnt in damps; the peculiarity of which process is that, as each brick contains in itself the fuel necessary for its vitrifica-tion, the breeze merely serves to ignite the lower tiers, and the heat gradually spreads over the whole. The general structure of a clamp is as follows :A number of walls, or necks, three bricks thick, about sixty long, and twenty-four to thirty high, are built slantingly against a central upright wall, which narrows upwards. The sides and top are cased with burnt bricks. Cinders (or breeze) are distributed in layers between the courses of brick, the thickest strata being at the bottom. A single clamp will contain from 200,000 to 500,000 bricks. For firing the clamps, live holes or flues (9 inches by 7) are left in the centre of the upright, and at every seventh neck or so, extending throughout the thickness of the clamp. These are filled with faggots, and fired by a coal fire at the end of each vent; and the fire ignites the adjacent breeze. Once the clamp is fairly lighted, the mouths of the live holes are stopped with bricks and plastered over with clay, and the clamp burns till all the breeze is consumed, usually from three to six weeks. After cooling, the bricks are removed, sorted, perhaps, and stacked. (For a fuller account of the most approved methods of building clamps, the reader is referred to Mr Dobson's excellent little treatise on brick-making, to which we are indebted for many of the details given in this paper.) Notting- In the Nottingham district a very hard marl is often ham used in brickmaking; and as ordinary weathering and tempering would not make it sufficiently plastic, it is sub-jected to grinding between rollers, the hard lumps and pieces of limestone being thus crushed to powder, all pebbles and hard stones having been previously picked out by the hand. The wash-mill is only used in making arch-bricks, and the pug-mill is dispensed with, the tempering of the clay, after grinding, being done by treading and spade labour. Sometimes the clay is kept in damp cellars for a year or more to ripen. Brass moulds (technically called copper moulds) are used, and the moulder, after filling the mould, works over the clay, first on one side then on the other, with a flat implement called the plane. A boy takes the mould with its contents to the floor, where he turns out the brick, and then puts back the mould on the stool, the moulder meanwhile rilling another mould. The bricks are sprinkled with sand on the floors, and turned twice at a few hours' interval, and are then taken by boys to the hovel or drying-shed, when they are built in hacks. They are burnt in kilns, which are made with four upright walls and a sunken floor. On the two sides of the kiln there are shallow pits with lean-to roofs to protect the fuel and fireman. The doorways are narrow openings at the ends, a step above the ground, and the fire-holes are arched openings opposite each other in the side of the kiln, lined with fire-bricks. Narrow openings or flues are left between the bricks, connecting the opposite fire-holes. Each brick has some free space round it for passage of heat. The fuel employed is coal. Stafford- In the Staffordshire Potteries it is a common practice to ihire. pass the marl through several pairs of rollers, and then mix some three or four marls together, with water, by spade labour. For ordinary bricks the ground marl is mixed with marl that has been tempered but not ground. The pug-mill is employed for tiles and dust bricks,the latter so called from coal dust being used when they are moulded. The bricks are moulded by the slop-moulding process, the mould being dipped in water only before using ; the brick is emptied from the mould on the floor. (The other process is distinguished as that of sand-stock moulding.) The oven used in burning is of circular form, with spherical top, and will contain about 8000 bricks. Bed, blue, and drab bricks are produced in the district, besides the dust brick just referred to, which is used for the paving of footways..
In Holland, the chief material used for bricks is the Holland, slime deposited in rivers and arms of the sea. It is collected in boats by men with long poles, having a cutting circle of iron at the end, and a bag net with which they lug up the slime. Hard bricks are made of a mixture of this slime with sand from the banks of the River Maas. The ingredients are well kneaded together, and the mixture is deposited in heaps. The mode of moulding and drying is similar to that used elsewhere. The kilns are square and will sometimes hold as many as 1,200,000 bricks. Peat turf is used in firing.
For an account of brickmaking in India the reader is referred to a paper by Major Falconnet, R.E., in the Pro-fessional Papers on Indian Engineering, May 1874.
Thus far only brickmaking by hand has been spoken of, but of recent years there has been no little activity in making by the invention of brickmaking machines, with a view to economy, certainty, and rapidity of production, and improvement in the quality and appearance of the bricks. It is only in brickmaking on a considerable scale, of course, that moulding by machinery can present much advantage over hand moulding, since the cost of moulding bears so small a proportion to the total cost. The various machines that have been offered to the public may be arranged in two classes,those which operate on the clay (with moderate pressure) in a moist and plastic state, and those in which the material used is pulverized and dry, or nearly so. A denser brick, and one less liable to shrinking, is produced in the latter case; but much care is needed in preparation of the clay, and a much stronger compression is required, to ensure the proper tenacity. The different arrangements of rollers and pug-mills for preparation of the clay, whether plastic or dry, we need not here describe at any length. Rollers and pug-mill are sometimes combined, forming a composite machine. Two or more pairs of rollers are sometimes arranged one set under another, the closest at the bottom; and opposing rollers are driven at different speeds so as to produce a rub as well as a squeeze, thus promoting disintegration. As to that class of brickmaking machines proper in which plastic clay in used, we find, in some examples, a continuous length of clay forced out from a vertical or horizontal pug-mill through a suitable mouth-piece, and the column divided into bricks by wires or otherwise. Of mouthpieces, some are simple dies, or dies fitted with cores to make hollow bricks ; in others the mould is lubricated by a constant stream of water; in others, again, the mouthpiece is made with two or four rollers covered with thick cloth, which are perforated with small holes, and filled with oil to lubricate the faces of the bricks. In cutting, a frame of parallel wires may be moved across, either while the clay is at rest, or while it is in motion, by the wires being moved obliquely at an angle to compensate for the speed at which the clay travels. Or the clay may be cut by radial wires of a wheel, or again by metallic discs. Another variety of treatment of plastic clay is that in which the clay is pressed from the pug-mill into moulds of the form of brick required. In one such machine, a mould-block, with two moulds, moves backwards and forwards under the pug-mill, one mould receiving a charge while the other is having the brick pressed out of it by a piston. In another, the moulds are arranged radially round the border of a circular table, which revolver under the pug-mill. There are piston rods in the mould which ascend an inclined spiral plane, and thus gradually lift the bricks out of the moulds, whence they are taken by a boy and placed on an endless band, which conveys them away. In another machine, also with revolving table, two moulds receive the charge of clay at once. While these are being filled the two that had just been filled are being subjected to considerable pressure, and the two bricks that had been pressed immediately before are in process of delivery out of the moulds, and on to a flat belt which takes them away. (This machine is also suitable for dry clay.) In yet another, a cylinder revolving under the pug-mill presents to it successively four brick-moulds, each of which, on reaching the lowest point, is made to deposit its brick on an endless band. The annexed drawing represents one of Messrs H. Clayton, Son, & Howlett's single delivery machines for brickmaking with plastic clay. After what has been said little description will be neces-sary. A is the pair of rollers, B the pug-mill, C the stream of issuing clay, which a little further on is cut across by means of the wire frame D. The bricks are then removed to the barrow E. These machines are often constructed for double delivery.
As an example of the second class of machines,those for working dry, or half-dry, and non-plastic material,we may take another machine constructed by Messrs Clayton. It affords a good practical solution of the problem of making bricks from coal shale, bind, fire-clay, or the like. The arrangement is shown in figs. 3 and 4. In fig. 3, A
rollers C on the lower extremities, in con-tact with which work two pressing cams D on the main shaft. The upper pistons E are attached as shown to a cross-head above, which is moved up and down in its guides by connecting rods and two cranks on the main
FIG. 3.Section of Machine for Non-plastic Material.
is a pan roller mill, in which a pan containing the raw material is driven round under rollers; there are perfora-tions in the bottom, through which the ground clay escapes, and is swept by arms into a general receiver, whence a band with buckets conveys it to the hopper of the mould-ing and pressing machines C, of which fig. 4 gives another view. Here the moulds are contained in a box at B, bolted between the standards. There are two sets of pistons, one above and the other below the brick-moulds, and they simultaneously press the top and the bottom of the brick in the mould. The lower pistons are attached to a cross bar which slides in vertical guides in the standards, and has friction rollers C on the lower extremities, in con-tact with which work two pressing cams D on the main shaft. The upper pistons E are attached as shown to a cross-head above, which is moved up and down in its guides by connecting rods and two cranks on the main
FIG. 4.-Part of Machine shown in section in fig. 3.
shaft. These pistons are hollow, and are heated by steam to prevent the brick-earth adhering to them. The prepared material is supplied to the two moulds by a feed-box which slides to and fro under the feeding hopper of the machine,
and thus passes alternately under it and over the moulds, conveying sufficient each time to fill the latter. The bricks are delivered from the moulds by the lower pistons, which are forced upwards by the complete revolution of the cams, and the newly-made bricks are forthwith moved forward by the approach of the feed-box with a fresh charge of the material. In another dry-clay machine constructed by Messrs Bradley and Craven of Wakefield, two or three distinct pressures can be given to a brick, and by this paeans the air is gradually forced out from the interstices, and the brick consolidated to a greater extent than can be effected by a single pressure.
The varieties of brickmaking machinery are too numer-ous to be separately noticed, however briefly, but the fore-going may suffice to illustrate the general principles involved in their construction. With suitable modifications, perfor-ated or hollow bricks are frequently produced, on which there is a saving in cost of carriage, and also in mortar and labour.
Onburrit Among the objects at the International Exhibition of bricks. 1874 there were several varieties of brick prepared with-out burning, according to a process devised by Messrs Bodmer. They are made by intimately mixing certain materials of the nature of cements or mortars, and squeezing the mixture into the desired shape by hydraulic pressure in a specially-constructed machine. Sand and selenitic lime are the constituents of one kind of brick; these substances, together with Portland cement, of another ; and a very serviceable kind of brick is prepared from blast-furnace slag, which, consisting chiefly of silicates decomposable by lime, is just as suitable for the purpose as the volcanic products, trass and pozzuolano, which have long been employed. The bricks give good results on application of the usual tests. Floating The old invention of floating bricks (known to Pliny) was bricks. completely lost till M. Fabroni discovered they could be made from the earth known as fossil meal, which is abundant in Tuscany, and is found near Castel del Piano in the territories of Siena. Hoffmann's For the drying and burning of bricks, the construction kilns. 0f kjjQg according to Hoffmann's method is a remarkable improvement of late years. These kilns are formed by a series of arched chambers connected by passages to one main chimney flue, each passage or flue having suitable dampers to regulate the heat at any desired point. Small coal, slack, or peat fuel may be used, which is fed in from the top of the kilns through small openings. The waste gases from the burning and cooling chambers are made to pass successively into other chambers and give out their heat before escaping to the chimney, thus completing the drying, and effecting a partial burning, of newly-made Jricks before the actual firing of the chambers in which these latter are newly set. Such kilns are no doubt beyond the means of most brickmakers, but it is perhaps a question for consideration whether bricks must necessarily be burnt in immediate proximity to the spot where the clay is obtained.
In an instructive report on the manufacture of bricks, drawn up a few years ago by a committee of the Manchester Society of Architects, the following points were specified as requiring attention, in order to improve the character of the common brick :(a) Greater care in cleaning the clay and in thoroughly tempering ito (b) variation in the size of moulds, so as to produce uniform sized bricks from various clays; (c) moulding the brick with material of such consistency that it may not become misshapen by the effects of its own gravity ; (d) greater regularity of surface of the drying-ground ; (e) protection from extreme variations of temperature and rain in drying ; (/) less frequent and more careful handling in the process of drying, so as to preserve the edges; (g) a means of burning whereby the amount of firing shall be under control. In experiments on the absorption and retention of moisture, it was found that the bricks which parted most readily with their moisture at first were the longest in drying, and vice versa.
Tiles, being a thinner ware than bricks, have to be made of purer and stronger clay, and require more care in treat-ment, but the process of manufacture is not essentially different. The numerous varieties of tiles may be roughly arranged in three classes, viz., paving tiles, roofing tiles (including the flat plain tiles, the curved pantiles, hip, ridge, and valley tiles), and drain tiles. In weathering, the clay is spread in layers of about 2 inches thickness during winter, and each layer is allowed the benefit of at least one night's frost before the succeeding layer is put upon it. Sometimes the weathering is effected by sunshine. The comminuted clay is next placed in pits and allowed to mellow or ripen under water. Then it is passed through the pug-mill, and the tempered product, if necessary, slung (that is, cut in thin slices with a piece of wire fixed to two handles, in order to detect any stones), and then passed through the pug-mill again, after which it is generally ready for moulding. To take the case of pantiles (hand-moulded), the moulder turns the tile out of the flat mould on to the washing-offframe, on the curved surface of which, with very wet hands, he washes it into a curved shape. Then he strikes it with a semi-cylindrical implement called the splayer, and conveys it on this to the flat block where he deposits it, with the convex side uppermost, and, removing the splayer, leaves the tile to dry. The tile is afterwards beaten on the thwacking frame, to correct any warping that may have occurred, and trimmed with the thwacking-knife. In the kiln, which is constructed with arched furnaces at the base of a conical erection called the dome, the tiles are closely stacked in upright position, on a bottom of vitrified bricks. The fuel used is coal, and the burning continues usually about six days. In making pipe drain tiles, the clay is first moulded to the proper length, width, and thickness, then wrapped round a drum; the edges are closed together, and the tile is carefully shaped by the operator's hand, sometimes assisted by a wooden tool. Tiles as well as bricks can be made by machineryo with suitable dies, almost any form of tile may be thus had, which is producible by the advance of a given section of clay parallel to itself. In other machines pressure is exerted on the clay in a mould.
The manufacture of tessera; and encaustic tiles has been brought to great perfection in recent times, through the enterprise especially of Mr Minton. It is a revival and extension of a very old art, which originated, probably, with the Greeks. The tesselated pavements of the Bomans, of which many specimens are still extant, were formed of small pieces of stone or marble of various colours, bedded one by one in a layer of cement. The principle on which tesseras are now made, is that dry and finely-powdered clay, compressed between steel dies, is changed into a very com-pact and hard solid body, a fact first observed by Mr Prosser in 1840. The solid pieces, which are thus pro-duced in a screw-press, are enclosed in earthenware cases or pans, call saggers, and fired in a potter's kiln, after which they are ready for use, unless they are required to be glazed, in which case they are dipped in a glazing composition and again fired. The mode of setting the pieces differs essentially from the Boman method. In manufacture of the tiles called encaustic, in which various designs are pro-duced by addition of clays of different colour from that of the ground, the clays first undergo sundry washings and purifications. A portion of the kind which is to form the ground first receives an impression, in the plastic state, from a plaster in relief. The bulk of the tile is made up with coarser clay added in a frame, and this is solidified in a screw-press. Then conies the filling in of the design, which the maker does by spreading the coloured clay in a creamy or slip state on the indented surface. After a few days' evaporation, the surface is scraped or planed, and the tile passes successively to the drying house and the oven. The colours desired in encaustic tiles are some-times those given by the clay in ordinary treatment, some-times they are obtained by staining with manganese, cobalt, etc. The products of this branch of manufacture are much admired.
The fine ornamental bricks of various shape and colour known as terra cotta have of late been much used, especially in the facing of public buildings, and with the happiest
effects. (A. B. M.)