The ware can no longer be packed one piece upon another, as in the previous firing, for the fusioo of the glaze would cause the piecee to adhere, and great damage would ensue. The ware is therefore separated by the insertion of props of refractory clay, made in such form that as small a part of the ware as possible shall be touched. Fig. 1156 shows a pile of plates, tiles, or saucers, supported and separsted by hollow thimbles with poioted arms. The Baggers with their contents are built up in a kiln similar to the one employed for the first firiug, only somewhat smaller. The saggers, AB ill the previous case, are made airtight by the insertion of rolls of plastic clay. The firing lasts some 18 hours, and its progress is tested by the removal of pieces of ware, similar to that being fired, and previouely dipped in the same glaze. The test-pieces are usually made on purpose, and pierced in the centre to facilitate removal.
Supports.—Gres.t ingenuity has been expended in devisiog and manufacturing the supports for ware undergoiog the firing for glaze. Fig. 1157 represents a press for forming the supports of stilts A B. The arm and handle z turn rigidly upon their axis. If the handle bo depressed, the vertical rod u ia also depreseed. When pressure is removed from the handle, tho rod Pt is raised once more by the action of a counterpoise. When u is in the posi tion shown in the figure, a strip of plastie refmetory clay is placed upou the die or mould, and is forced to adapt itself to the form of the mould aud plunger, by the preseuro of the de seending rod u, to which the plunger is attached. When the pressure is re moved by the action of the counter poise, the formed support may be raised from the mould by depressing the treadle. Minute apertures are pierced both in the mould aad plunger, to permit tlio escape of imprisoned air, and consequently to ensure the sharp ness of outliue of the support or cock spur. Machines are now iu use which produce 100 supports iu one action. The moulds, as iu the press already desoribed, are in two halves, one being attached to a plunger, and the other movable. The moulds contain the number of impressions sufficient to pro duce the required number of supports. There are several duplicates of the lower movable half of the mould, and in this alone are the apertures for the eecape of the air. The clay is supplied in a continuous stream from a minia ture expressing-machine. After the clay has been inserted, and pressure applied, the lower part of the mould, which contains the supports, is removed, and another is sub.9tituted. The mould and supports arc heated, and the supports sre readily extracted as soot, as the clay begins to contract.
After the supports are removed, the apertures in the depressions are cleared by pressing the mould upon a tool containing an equivalent number of points. The mould is then rubbed with mineral oil, and replaced under the plunger. Supports require to be burnt in the same manner
as ordinary earthen-ware.
Terra-cotta and Architectural Pottery.—Terra-cotta is a term commonly applied to works having an artistic character, made of clay, and burnt, sometimes painted and glazed, but more frequently unglazed. The fabrication of fictile works known by this name was common to all the great natioos of antiquity ; and of late years, much progress has been made in England, France, Germany, Italy, and other countries, in reviving the manufacture of useful, ornamental, and domestic articles in terra-cotta, and in applying this material to architectural purposes.
The clay anciently used in the small vessels and ornaments is fine in texture ; the larger pieces are made of rather coarser clay, combined with pulverized lava, pumice, or potsherds. They are generally much lighter than moderu works of a like size. Some of the ancient pottery commonly called " Samian ware," of a beautiful coralline red, we have never perfectly imitated ; there is much yet to discover relating to ancient pottery of this class. Vauquelin made analyses of fragments of Greek terra-cotta, and gives the following as some of the constituents :—Silica, 53 per cent. ; alumina, 15; lime, 8 ; oxide of iron, Ste., 24.
Between the 12th and 14th centuries, large and sumptuous edifices were erected in N. Italy of brick and terra-cotta, the latter taking the place of stone and marble for cornices, panels, string courses, and brackets. Many examples of brick buildings with terra-cotta mouldings and orna ments exist in England, having been erected mostly between the 13th and 16th centuries. Generally the use of terra-cotta died out in this country with the Tudors, and except a slight revival of moulded brickwork about the 17th and beginning of the 18th century, architectural terra-cotta was not practised until the time of George III. Towards the close of the 18th century, coeval with the great improvements made by Wedgwood in pottery, a most important advance for reviving the use of terra-cotta was established in Pedlar's Acre, Lambeth, by a lady named Coade. At these' works, capitals and bases of columns, coats-of-arms, pedestals, friezes, bases, statues, balustrades, archivolts, and terminals, were made ; and at the commencement of the present century, terra-cottas frorn Coade's works were to be met with in all the best parts of London and the provincial towns. Sculptors were employed upon models for this pottery, some of whom afterwards touk to manufac turing terra-cotta on their own account. Among them was Rossi, who executed statues, capitals, and other ornaments in terra-cotta for St. Pancras church ; and Bubb, who modelled and rnade the frieze in front of Her Majesty's Theatre, and most of the statues on the cornices, and in the tympani of pediments in Regent's Park.