Common Black JAPAN Grounds on Iron or Copper, produced by means of Heat.—For forming the common black japan grounds by means of heat, the piece of work to be japanned must be painted over with drying oil; and, when it is of a moderate dryness, must be put into a stove of such degree of heat as will change the oil to black, without burning it so as to destroy or weaken its tenacity. The stove should not be too hot when the work is put into it, nor the heat increased too fast; either of which errors would make it blister: but the slower the heat is augmented, and the longer it is continued, provided it be restrained within the due degree, the harder will be the coat of japan.—This kind of varnish requires no polish, having received, when properly managed, a sufficient one from the heat.