ENAMELING SLATE WASTE BRICK.
Some ten years ago, when first the manufacture of brick and tiles from slate waste commenced in North Wales, the white-glazed brick was successfully produced by the following process and recipes : The process is called the Biscuit-brick process—that is, the firing of the brick only slightly at first, all care being taken in setting and drawing the bricks so as not to damage them in any way. The brick need to be fired at about half the customary heat for the first fire; they must then be taken to the dipping house to be dipped in the body and glaze. Having everything in readiness, dip the part required to be glazed in clean water ; you then pass on the brick to the next hand, whose dip will be the white body ; then on to the next hand, whose dip will also be the white body ; again, pass on the brick to the fourth hand, whose dip will be the glaze. Allow the brick to dry a little ;
then take a knife and scrape off all body and glaze that may have run over the side of the brick. The brick can then be set in the kiln to be fired again. The slate waste, however, is a ticklish material, and will not stand a hard fire. The heat it will take is a good red clay heat ; it will thus be seen that a down-draft kiln will not i3o for glazing slate waste. It must be fired in a kiln where all the flash-heat can be kept from the brick—the kiln generally used is the Simmer muffle-kiln. The kiln itself when set with brick is almost a box-kiln. The brick must be fired gently at first, and when on full fire it must not be neglected or allowed to sink too low. The firing should be continued until the glaze has run bright.
The following are the recipes of body and white glaze :