Minton hesitated to order machines for forming tessera) and tilea beyond the sizes of 1 in., in., and in. ; but Prosser made the necessary toola, and in 1844-1845, tiles of large size and various elinpes, and slabs 3 ft. long, were fabricated. Michael Hollins, the present proprietor of the tile worka, laboured most zealously from the firat in the fabrication of the raw material and colours.
Having related something of the early history of this important improvement in the cenunic art, which has brought about such vast changes in architectural decoration, rind which is making every day fresh stridea, we will enter upon a description of the maehine first employed to make teeserte, and which, with a few modificationa, is still used for tesserte and small thin tiles, a more powerful machine and hydraulic presaes being used for large and thick tiles, and other flat surfaces, aud for making bricks from powdered clay. The preparation of the powdered material may be explained in a few words. For teaaera), it frequently consiats of alumina, silica, and haryta, mixed with some metallic oxide for colouring matter. Tito difference between the new process and the old is that the clay or earthy material for making the tessera), tiles, or other artielea, instead of being used in a plastic stato, is used in dry powder. The materials may be of the same character, and, up to a certain stage in their combination, they undergo a like preparation. For example, they are mixed with water, and ground by machinery, to thoroughly incorporate them, and, in a atate, are paased through fine sievea, to remove all coarse particles; aud when thia done, the clayey paste is partially dried by the heat of a slip-kiln, and made up into balls, which, when perfectly dry, are ground in a mill ; and the dry ground inaterial, for fine aurfaces, ia passed through sieves, to prevent the risk of any coarse particle or dirt getting into tho articles which aro to he moulded.
Tiles must bo classified rather by the processes of their manufacture, than by the materials of which they aro composed. Tiles may be made by the same process, and yet may present as great a difference in texture as fire-ware on the ono hand and vitreous stone-ware on the other. The body most commonly used is that of ordinary whito earthen-were; but for coloured tilea, and for a backing to a surface of superior quality, mixtures of local marls and fire-clays are largely employed. There are two principal processes, which may be distinguiehed as the
wet process and tho dry process. By the former, tiles can be made hy hand, or by mechanical pressure ; by the latter, by mechanical pressure only. In making plain tiles by the wet process " bats" of plastio clay are prepared in the ordinary way hy manual or mechanical " batting," and are either cut to any required dimensions, or are beaten into a metallic mould. s made as described aro burnt in saggers, and reburnt after dipping in white or coloured glazes. The backs of tiles, whilst still plastic, are alwaye impressed with amall holes or depressions, which may form a key for the cement when they are applied to walla or other surfaces. So-called " Palisay" and " majolica" tiles are made from plastic clay " bats," which have received a raiaed pattern on their surfaces from a depressed pattern sunk into the mould in which they have been pressed. After first burning, the Palimy tiles are dipped into transparent coloured glazes, and the majolica tiles into opaque enamel slips.
The dry process consists in eousolidating clay powder by mechanical pressure. The clay powder, having heen damped, is placed upon a metallic block of the size of the tile to be produced, surrounded by a movable collar, and is compressed by the descent of a plunger into the niould so formed. The pressure is communicated to the plunger by a vertiaal screw, and the momentum is obtained from a horizontal fly-wheel or weighted arm. The compressed powder is removed by moana of a pedal, which lowers the collar or edge of the mould. The tiles thus produced may be either large or small, according to the power of the presses employed. Small tiles and tesserte are made by girls in small hand-presses. The moulds can be so made that several tessera) can be pressed at one motion. The compressed tiles are burnt for biscuit and glaze in the same manner as thew made by the wet process. The compression of powder as a means of manufacture is nut now limited to the production of tiles ; at the present time, plates and gallipots are beiug made by an application of the same procees. Coloured patterns may be inlaid in tiles hy either pieces..