FIRING.
The steaming or water smoking ofenamel brick should re ceive the closest attention, as, without great care being exer cised, it is possible at this stage of the work to ruin an entire kiln of brick. While the enamel brick are on the smooth boards in the drying room after being dipped, the exterior of the brick will become thoroughly dry, but considerable moist ure will still be present in the centre of the brick when they are removed from the boards to be conveyed to the kiln for firing. If this moisture contained in the interior of the brick should be drawn too suddenly to the surface by subjecting the brick too quickly to a high heat, the enamel surfaces of the brick will be stained with a black-bluish streak down the center, thus ren dering the wares unsalable. Other defects engendered by a too quick drying off of the moisture will result in flawed, cracked, shaky or burst brick.
When the water-smoke fires are started in the kiln, the heat should be raised very slowly, and at no period of the two nights and three days devoted to the drying of the brick in the kiln, should the grate-bars be more than one-half covered with fire. During the water-smoking of the brick, as much air as possible should be admitted into the kiln, and if the fire holes are provided with doors, these doors should be allowed to stand wide open. After this preliminary stage is passed the intensity of the heat should be gradually increased, and by the third day all the brick in the kiln should be about red hot, and when once under full fire the kiln must not be neglected or allowed, under any circumstances, to cool down, but the fires must be steadily continued until the glaze has run bright. The
test-proofs used should be in the shape of a cup with a hole in it so as to make them easy to draw from the kiln. This test proof, both inside and outside, should be enameled and glazed. The trial pieces should be drawn out from each end or side of the kiln when on looking through the peep hole into the inte rior of the kiln the flame will appear to be one solid white mass ; none of the brick being perceptible through the white heat.
An examination of the test-proofs at this stage of the burn ing, the proper enamels having been used, will show them to have a sweaty or greasy appearance, thus giving evidence that the enamel on the brick is in the incipient stage of fluxing. If the trial pieces have this sweaty or greasy look, then you must force your fires to their utmost, increasing the heat to as high a temperature as is possible, and in the meanwhile drawing out one of the test-proofs at intervals of about one hour to learn precisely the progress which is being made towards the com plete fusion of the enamel.
Finally, when the test-proof has been drawn having a glassy smoothness of surface, the time is now arrived when firing must stop. All the fireplace doors and every part of the kiln through which cold air drafts could find an entrance into the interior should be carefully daubed so as to make the kiln per fectly air-tight.