To produce a raised design upon a plate of copper, or as it is rather erroneously styled, “Engraving in Relief,” the operation is thus performed:-- The plate upon which the design is to be raised having had the conducting wire soldered to it, is covered with a coat of wax about one-eighth of an inch or less in thickness, and upon the surface of this coat the design is drawn. With a graver, the end of which must be of the form of a thin parallelogram, so as to make grooves in the wax equally broad at the bottom as at the top, the lines of the drawing are to be carefully cut down to the plate; care being taken that the plate is perfectly cleaned throughout each line, and also that the grooves are not narrower at the bottom than at the top. In order to lay the surface of the copper at the bottom of the grooves perfectly bare, the plate must be immersed in diluted nitric acid (three parts of water to one of acid), and the particles of wax that may have escaped the graver are driven off by the fumes of the acid. The plate is then placed in the apparatus, the circle closed as before, and the operation commences. As the particles of copper require a metallic base, they avoid the wax and seek the metal in the grooves; they there attach themselves to it, and to each other, until the hollows are quite filled up, when the plate is removed. If the surfaces of the ridges thus built up be not perfectly smooth, a piece of pumice stone or smooth flag, with water, being rubbed to them, will soon reduce them, after which the wax can be melted and cleaned off with spirits of turpentine; and so firm is this formation of metal thus raised, both in the adherence of its particles to each other and to the original plate, that it may be printed from at any ordinary printing-press. One general remark applies to the production of electrotype copper, and it is, that the strength and solidity of the formation depends upon the slowness and deliberation of the process. The more slowly and deliberately the particles separate from the solution and proceed to their places, the more fitly they appear to take them up, and the more firmly they adhere; whilst on the contrary, if the operation be hurried, the metal is brittle, so much so as sometimes to powder under an ordinary pressure. The thicker and finer the partition of plaster between the two fluids, the more slightly are they connected, and consequently the slower is the circulation of the electricity. The proper length of time to be allowed for the process varies according to the nature of the work, and the strength or solidity required. Forty-eight hours seems to be the least time for forming a design in relief, and somewhat more than a week for a plate with sunk lines.