=Porcelain Enamelling.=--The cast-iron bath or stove is heated to redness in a muffle furnace. On withdrawal from the furnace it is placed by the helpers on a table capable of being turned in every direction. Enamel powder is then dusted on to the heated metallic surface through a sieve attached to a long wooden handle, held by the duster, who protects himself from the intense heat by a mask and an asbestos cloth covering. [Illustration: FIG. 12.--The first glaze is sprayed on with an aerograph. The portion of the stove to be glazed is shown on supports on the sliding table, which is half out of the cabinet. When the casting is fully in the cabinet, the end piece and the centre piece close the cabinet sides, and, fitting on a felt beading, make an air-tight joint. The spray, shown in front of the cabinet, is worked through the holes in the glass front. Exhaust is provided at the top.] _Dangers and Prevention._--The heated column of air carries up much of the powdered glaze as it is unevenly distributed by jolting the handle of the receptacle, and in the absence of very efficient exhaust ventilation this dust will, as the current of air strikes the roof and cools, fall down again. The hood placed over the bath must have steep sides and be brought down as low as is possible without interfering with work, and the duct leading to the fan must be unusually wide, so as to be able to cope with the up-rush of heated air. If the sides of the hood be shallow, not only will the dust fail to be removed, but the hood itself may become so hot as noticeably to increase the discomfort from heat to which the men are exposed during the three or four minutes, five or six times an hour, that the dusting operation lasts. A method has been patented by M. Dormoy of Sougland[29], Aisne, France, for carrying out automatically in a closed chamber the process of dusting on to small red-hot castings, such as are required in the manufacture of stoves. It is not applicable for baths. Occasionally, in the case of small castings, again, the enamel is sprayed on by means of an aerograph. For this excessively dangerous process we have seen simple and ingenious devices for carrying it on quite safely in a space under negative pressure, and covered in except for the necessary openings through which to work the spray (see Figs. 12, 13, 14).[A] [A] The cabinets have been patented by Messrs. Wilsons and Mathiesons, Ltd., Leeds, by whom they are made and supplied. Since using them there has been no trace of illness among the persons employed. [Illustration: FIG. 13.--After firing the casting is lifted out for treatment with dry glaze, which is sprinkled on with a sifter shown on the table. The turntable enables the operator to manipulate the red-hot casting more easily.]