The glaziers differ in their composition in all manufactories; most, however, have oxide of lead for their basis. The ingredients being mixed with water, and well ground, the. glaze is ready for use, in which the vessels are dipped. On drying, which takes place instantly, the water contained in the glaze being absorbed by the porosity of the vessel, it is covered with a fine white powder, of a regular thickness; this, when fired, becomes vitreous, or assumes a glass-like appearance, and, from its transparency, the blue pattern underneath is rendered perfectly visible. In the last firing, especial care is taken to keep one piece from touching the other, or the whole would fuse into one united mass. Great attention is also requisite in the firing, not to give too much or too little heat, either extreme being injurious: the fireman in this, as in the other firing, draws out trial pieces from the oven, with an iron rod, to ascertain the proper degree of heat.