Page:Encyclopædia Britannica, Ninth Edition, v. 8.djvu/198

Rh 188 ENCAUSTIC TILES of abbots and other church dignitaries, also enter largely iuto the decorations of ancient encaustic tiles. Amongst the most interesting examples of these pavements, found in situ, is that in the chapter house at Westminster, which about the year 1840 was laid open to view by the removal of a wooden floor previously covering it. It is probably of (he time of Henry III., in whose reign it is recorded that the king s little chapel at Westminster was paved with &quot; painted tile,&quot; &quot;mandatum est, &c., quod parvam capel- lam apud Westm. tegula picta decenter paveari faciatis. &quot; Rot Glaus. 22 Henry III. M, 19, 1237-38 A.D. The tiles of this pavement comprise subjects which may be taken to represent the king, queen, and the abbot, also the legend of King Edward the Confessor bestowing a ring, as alms, on St John the Baptist, who appeared to him in the guise of a pilgrim, besides other curious historical designs. The tiles from Chertsey Abbey, Surrey, now in the architectural museum, Westminster, are also amongst the oldest, and, at the same time, the finest and most artistic yet brought to light. They present a remarkable series of illustrations from the English romance of Sir Tristram, and of incidents in the history of Richard Coeur-de-Lion. These tiles were all found in fragments, but have been put together with great care. Traces of the ancient manufacture of encaustic tiles have been found in several places in England, and the remains of kilns containing tiles in various stages of manufacture have been discovered at Bawsley, near Lynn, in .the neighbourhood of Droitwich, as well as in other localities, by which an interesting light has been thrown upon the ancient process of production. In almost every instance these tiles were covered with a yellowish glaze, composed principally of lead, similar to that now used in the commoner English earthenware manufactures. The modern revival of the art dates from the year 1830, when a patent was granted, with this object, to Samuel Wright, a potter of Shelton, in Staffordshire ; but, he hav ing failed to bring his experiments to a profitable result at the expiration of the term, a further extension for seven years was granted him. In the year 1844 his patent right was purchased, in equal shares, by the celebrated china manufacturer Herbert Minton and Mr Fleming St John, the former carrying on the manufacture at Stoke-upon- Treut, and the latter at Worcester, in partnership with Mr George Barr, an eminent china manufacturer of that city. Four years later, the firm of which Mr Minton was the head re-purchased the residue of Mr St John s share of the patent right, who about the same time relinquished the manufacture. In the year 1850 Messrs Maw & Co. pur chased the remaining stock of encaustic tiles at the Worcester china works, and, on the expiration of Mr Wright s patent, commenced the manufacture on those premises, from which they removed to the present site of their works, at Benthall, near Broseley, Shropshire, whence the marls, peculiarly suitable for the purpose, had pre viously been obtained. The modern manufacture may be described under two heads viz., the &quot; plastic &quot; and the &quot; semi-dry &quot; or &quot; dust &quot; processes. The former, which was the only one employed up to the year 1863, is in every essential point the same as that used in mediaeval times, differing merely in the greater finish and perfection which modern appliances have effected, and probably also in the material of the moulds. It is not known of what those anciently used were made, but conjecture has suggested wood, firjd clay, and stone. The great difficulty of the manufacture consists in the necessity for introducing into a single tile the variety of different coloured clays or &quot; bodies &quot; which together com pose the design, it being essential that they should not only be perfected by the same amount of heat in the process of firing, but that they should possess an equal contractile power during each stage of the manufacture. The tile is first impressed from a plaster-of-Paris mould, bearing the pattern in relief, and set in a brass frame, upon which fits another frame, the dimensions and depth of which correspond with the size and thickness of the tile ; the pattern is thus sunk in the clay to a depth of about one-sixteenth of an inch, in the following manner. The workman first introduces into the mould what may be described as a sheet of refined clay of the desired colour for the ground of the pattern ; upon this facing, which forms a kind of veneer, is placed a thicker mass of a coarser kind of clay, and the whole is then subjected to screw pressure, which consolidates the two kinds of clays, and at the same time perfectly impresses the pattern of the mould ; the superfluous clay is then removed with a scraper, and a second veneering of fine clay, similar to that used for the face, is placed on the back ; the tile being removed from the- mould, the depressed parts of the design are filled with clay, of one or more colours, by pouring it in in a &quot; slip &quot; or semi-liquid state. The tile is then set aside for twenty- four hours to stiffen, and when the &quot; slip &quot; inlay has become nearly of the same consistency as the tile itself, the face is brought roughly to an even surface, by &quot; spreading &quot; the soft clay with a pallet-knife. The tile is then further allowed to dry till it attains the stiffness of wax, when it is &quot; finished &quot; by scraping the face with a steel scraper, until the inlaid pattern and ground are developed free from superfluous clay, and the edges are cut true to a square, when it is ready for the drying stove. When the drying, which takes from six to ten days, is completed, the tiles are placed in fire-clay boxes, known as &quot; saggers,&quot; containing from eight to ten each, which are then stacked, one upon another, in the kiln or oven. The process of firing occupies four days and nights, and has to be conducted with the greatest care, as not only the exact size and hardness of the tiles are dependent upon it, but also the perfection of the colours, with which object it is necessary to raise the heat very gradually, and to secure a regular circulation of air in the oven, so as to produce the exact degree of oxidization needed to bring out the desired colours in the materials used for this purpose. The pyrometers used in this part of the process consist of long narrow tiles, and the degree of heat is judged both by their colour and the gradual reduction in length which they undergo, each piece, as it is withdrawn from the oven, being measured in a gauge, with this object, the total shrinkage of the tile, in the drying and firing, amounting to about l inches in the foot. For purposes of paving, most of the modern encaustic tiles are used in the &quot;bisque&quot; or unglazed state, the glaze in the ancient tiles having apparently been employed with the object of covering the soft material of the tile itself, and of adding richness to the colour. Where glazing is found necessary in the modern tiles it is effected by dipping them in a combination of lead, alkaline salts, felspar, and silica, finely levigated in water, which is fused by passing them through a kiln specially constructed for the purpose. The semi-dry or &quot; dust &quot; process of manufacturing encaustic tiles is an adaptation of an invention patented in the year 1840 by Richard Prosser, by which articles of various kinds are moulded out of pulverized clay, in metal dies, by screw pressure. In the year 18G3 Messrs Boulton and Worthington, engineers of Burslem. patented a process by which the use of powdered clay (hitherto only used for tiles of one .colour) was applied to the manufacture of encaustic tiles. The design is formed by perforated brass plates, from one to six or seven being usecL according to