Muffles

—The paintings and the printed figures applied to the glaze of stoneware and porcelain are baked in muffles of a peculiar form. Fig. 897. is a lateral elevation of one of these muffles; fig. 898. is a front view. The same letters denote the same parts in the two figures. a is the furnace; b , the oblong muffle, made of fire-clay, surmounted with a dome pierced with three apertures k , k , k , for the escape of the vaporous matters of the colours and volatile oils with which they are ground up; c is the chimney; d , d , feed-holes, by which the fuel is introduced; e , the fire-grate; f , the ash-pit; channels are left in the bottom of the furnace to facilitate the pa age of the flame beneath the muffle; g is a lateral hole, which makes a communication acro the furnace in the muffle, enabling the kiln man to ascertain what is pa ing within; k , k , are the lateral chinks for observing the progre of the firing or flame; l , is an opening scooped out in the front of the chimney to modify its draught. The articles which are printed or painted upon the glaze are placed in the muffle without saggers, upon tripods, or movable supports furnished with feet. The muffle being charged, its mouth is closed with a fire-tile well luted round its edges. The fuel is then kindled in the fireplaces d , d , and the door of the furnace is closed with bricks, in which a small opening is left for taking out samples, and for examining the interior of the muffle. These sample or trial pieces, attached to a strong iron wire, show the progre of the baking operation. The front of the fireplaces is covered with a sheet-iron plate, which slides to one side, and may be shut whenever the kiln is charged. Soon after the fire is lighted, the flame, which communicates laterally from one furnace to another, envelopes the muffle on all sides, and thence rises up the chimney.