Of the Green Family from Harpole, Northamptonshire their Ancestors and Relatives

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Tuesday, 21 November 2017 06:20 AM GMT

Victorian Bricks, Tiles and Terra Cotta

by Gilbert R. Redgrave from Cassell's Technical Educator. (Written in the late 19th century.)

The manufacture of flooring tiles has, we think, made greater progress during the present century than any other branch of the ceramic art; and this industry as now practised in Staffordshire, presents many features of great interest, and differs in many respects from the manufacture of the coarser wares we have noticed in our previous chapters. The old fashioned 9 inch or 12 inch tiles made in wooden moulds in the same way as bricks are made, have now been almost entirely superseded by the thin machine made tile, which has scarcely one point in common with its clumsy prototype.

Tile making, or at any rate the manufacture of encaustic tiles, is now a business entirely alienated from the brickmaker, requiring as it does a most costly plant and a totally different mode of procedure to the heavier clay goods. In some country places, however, oven tiles, floor tiles, and quarries, are still made and burnt along with the bricks. We need not devote much time to the consideration of the tiles made from brick earth, as the process in every respect resemble those we have previously described. A carefully prepared clay is made use of, and the tiles when partially dry are smoothed over or trimmed with a steel instrument or knife, which gives them a silky, lustrous surface, and is supposed to make them more dense and durable. A tough clay is generally selected, such a clay, in fact, as would be employed for roofing tiles; the tiles are generally either 6 inches, 9 inches, or 12 inches square, though 4 inch tiles are sometimes made from the dense Staffordshire and Shropshire clays. The chief fault of these common tiles, which are often used for paving the floors of cottages and outhouses, is their great porosity. They absorb so much water that they are always cold and damp to the feet.

This defect is not so apparent in tiles made from the blue clays (i.e., those clays which, owing to the presence of iron, burn blue), which are much more suitable for paving purposes, though very unpleasant in point of colour. In many parts of the country it is customary to use the blue bricks and quarries for foot pacements; but owing to their almost metallic surface, it is necessary to roughen them artificially to render them less slippery. Mr. Page, the engineer of Westminster Bridgw, was so struck with the hardness and durability of the blue ware, that he employed 12 inch blue tiles for the foot pavements of the bridge; but they do not seem to have answered expectations, as they have now worn away so much as to have lost every trace of their blue colour, and in some plkaces have become very uneven. Thisd is rendered all the more conspicuous by the occasional insertion of strips of granite, which stand out a quarter of an inch more above the tiles.

Under the head of flooring tiles, we may also allude to the so called Dutch clinkers, which are largely used for paving purposes. They are in reality a species of small, hard burnt bricks, generally made from Gault or some similar clay, and employed for the interior of stables, for which, owing to their great hardness and imperviousness, they are admirably fitted.

Even so far back as the latter end of the thirteenth century, the art of making inlaid tiles or tiles which received their decoration from the insertion of a pattern in coloured clay, seems to have been practised in England. The pavements of many old halls and churches appear to have been formed of such tiles, many of which evince great skill and care in their manufacture. The revival of the art of making these tiles - which seems to have been lost or to have fallen into abeyance - is due to an English manufacturer, Mr. Herbert Minton, of Stoke, whose name is now invariably associated with "encaustic" tiles.

Before going further we may explain briefly what we vtake to be the meaning of the term "encaustic." We understand such materials to be truly encaustic, as have the various colours they display actually intermixed with the substances or clays from which they are formed, and burnt in, as it were, at the same time as the article is fired: a combination, in fact, of coloured "bodies,"as the clays in this state would be termed. Tiles formed thus by inserting for a considerable depth, or throughout their entire thickness variously coloured clays disposed in certain definite forms would be true encaustic tiles.

In opposition to such tiles, we have what are known as "decorated tiles," or those which have on a plain surface, a pattern printed in one or more colours. These tiles have thus all the appearance of true encaustic tiles; but they have, of course, no such qualities of wear. They are therefore used for wall tiles, hearths, etc., and for places where there is no traffic. They are verey copmmonly passed throgh the gloss oven, where they receive an ordinary fritted glaze. In some of these pseudo encaustic tiles, small bands of colour are printed round each of the edges, to represent the depth of the insertion of the coloured clays in the real tiles. A third description of tiles is known as majolica tiles, and here the clay receives a moulded or enriched surface in the biscuit state, and is then passed through the enamelling kiln and enriched with various opaque, glazed colours technically known as "enamel colours." These tiles, of course, are used solely for wall tiling.

Having thus explained the various kinds of tiles, we may pass on to a more detailed account of the process of their manufacture. The cay used for what we may call the foundation or body of an encaustic tile, has to be very carefully selected and prepared. We have already noticed in various other places, the manner of dealing with the clay in order to fit it for use, and in describing the mode of manipulating the clay for tile making in detail, we should have to repeat much of what has been said previously. The principle seat of tile manufacture is, of course, in the vicinity of the Staffordshire potteries, and the clay mostly used is the red surface clay of the district, and the buff coloured clay or marl. For those tiles which are required to be of a pure white colour, or which it is proposed to stain of a delicate tint, it becomes necessary to use the more expensive white clays of Dorsetshire and Devonshire.

The clays undergo almost the same nicety of preparation for tile making as would be observed in the case of pottery. The raw clay is first subjected to the action of the blunging mill, which consists of a set of long cutting knives like the teeth of a gigantic rake. These knives are inserted into a horizontal shaft, which is caused to revolve slowly in a pan or tank about half full of water. The action of these knives is to tear and beat the clay to pieces, and to mix it with water to the consistency of a thinnish cream. This cream, technically known as "slip," runs away by natural overflow to the evaporating pans or "slip kilns," and the heavier and more solid impurities in the clay sink to the bottom of the blunging mill, whence they may be from time to time withdrawn. In the condition of slip, any mixture of clays or introduction of colouring matter can be admirably and thoroughly effected. For some processes in the manufacture of encaustic tiles, as we shall see later, the clay is used either as slip or in a butter like state; but for ordinary pressed tiles it is used slightly damp as a powder.

The slip kiln, till recently in common use for drying or evaporating the water from the clay, consists of a number of parallel, horizontal flues, covered with fire clay quarries, and having a furnace at one end, and a lofty chimney at the other, in order to promote a sufficient draught. The floor of the slip kiln is surrounded with a brick margin, raised about twelve inches above it, and is laid at such an incline that, while at the end nearest the furnace where the heat, of course, is greatest, the liquid slip when first run on is 7 or 8 inches in depth; at the far end near the chimney the depth is not more than 2 to 3 inches. It is found by this means that the whole of the clay is ready to take off about the same time. Slip kiln builders have several fanciful regulations about the size of their flues, which they decrease very rapidly at the end of the kiln furthest from the furnace, deeming that in this way they produce a sharper draught into the chimney, the only actual result being that the flues very soon get filled up, owing to their shallowness, with the leakages through the joints of the cover quarries. The time required to evaporate a charge of slip on an ordinary sized kiln is from seventeen to twenty hours, and the clay is considered ready when it is all in a soft putty like condition. A long slip kiln is very liable to become partially caked and unfit for use, owing to its being overdried at one end before the other is ready.

Slip kilns are, however, being entirely superseded by the patent clay presses or wringing machines introduced by Messrs. Needham and Kite. By means of this invention the liquid clay is run into a number of linen clothes folded into a series of bags, and inserted between fluted boards placed in a frame. These boards are gradually driven together by hydraulic pressure, and the water in the clay is expelled through the pores of the linen wrappers; thus in a very short time the clay is dry enough for use, and when prepared in this way it is said to be better than that which has been boiled. Were it not for a heavy royalty now charged under the patent, and the great wear and tear in the cloths, this process would doubtless be universally employed by potters. For the manufacture of the clay dust, however, the wrtingers alone are insufficient, as the whole of the water must be exdpelled by means of kiln drying, before the clay can be ground. The dried clay is pulverised under horizontal stones, and if necessary dressed through a fine sieve.

The almost impalpable powder obtained in this way is now ready for use. As it comes from the mill it is not quite damp enogh to bind, and in order to moisten it equably and sufficiently, a curious process is now adopted. It was found that no system of sprinkling with water or other artificial mode of wetting it rendered it all equally damp. Advantage has therefore been taken of the sponge like action of plaster of Paris. Large beds, some four or five inches in thickness, of this material are prepared and carefully wetted; on these beds an even layer of clay dust is spread previous to its use, and this clay sucks up from the damp plaster excactly the proper amount of water to give it the required cohesion. From these beds, the clay is carried to the presses, which are cumbrous affairs, made much after the fashion of coining presses, having a screw to which is attached the lid of the mould and heavy arms to cause the revolution of the screw. The mould itself, made of course of metal, is formed by a depression in the otherwise level surface of the table on which rests the clay. The workman begins by scraping across into the mould enough of the powder to fill it, and roughly levels the surface by striking it with a straight edge. The screw or die is then brought down gently at first to expel the air, after which a sharp and heavy blow is given by rapidly swinging round the arms of the screw. By this second blow the clay in the mould is reduced to about two thirds of its former thickness, and is so far consolidated that it can readily be moved about and handled. The mould is relieved by an upward motion of the plate forming the bottom of ity, worked by a lever handle at the side of the press. On bringing this plate back to its former position, the mould is again ready to be charged with clay for the formation of another tile; the entire process occupying far less time than we have taken to describe it. For small tiles and diagonals or angle tiles, a divided mould making two at a time is commonly employed. A press on a very much smaller scale and worked by girls is used for making in exactly a similar way, the encaustic tesserae for mosaic work.

Of course, by using dust stained in various colours, while the clay is in the state of slip, tiles or tesserae of any self tint can be obtained by this process, and tiles made of pure white clay dust are in general use for decoration, either by transfer printing or painting. Before the tiles can be decorated, they must necessarily be burned into the state of biscuit, which is effected in "ovens" of the kind commonly used for burning pottery. These ovens may be described in a few words, as follows:- Round a circular chamber which may be from 14 to 16 feet in diameter, are arranged a series of fire places or "fire holes," varying from eight to twelve in number. These fire holes communicate with the oven by means of flues passing under the floor to an orifice in the centre, and small vertical chimneys built against the inner wall called the "bags." These ovens may be from 14 to 20 feet in height, and are covered in at the top with a brick dome pierced with openings (generally three to each fire hole) to carry off the products of copmbustion. A fierce upward draught is produced by surrounding the entire oven with a flask shaped chimney. This chimney, from the fact that its width at the base is such as to enable the workmen to attend to the fires under cover, is called the "hovel." The goods to be fired are enclosed in oval boxes of fire clay called "seggars," to protect them from the flames which freely enter the oven through the floor and bags. Some tile makers have introduced seggars of a square form which can be better filled with tiles than the round or oval boxes, but are said not to last so long. These seggars when filled are placed one above the other in stacks, sometimes twenty five seggars in height, called "bungs." In firing a biscuit oven, the usual precautions are taken to raise the heat very slowly, so that the goods are "smoked" for many hours before the full firing, which lasts about forty eight hours, is commenced. All tiles have to be first fired in the biscuit oven, and for plain encaustic tiles, this is the only firing required.

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