3690. To Use Metal Moulds

3690.     To Use Metal Moulds. The mould in fusible alloy does not require to bo black-leaded, but the surface to be electro-typed must be prepared with turpentine, etc., (see No. 3673 (Coating for Copper Moulds)), and the back and edge must bo protected by a coating of wax or other non-conducting material; it may bo connected with the zinc pole by putting a wire round its edge previous to laying on the non-conducting substance, such as tallow or wax, which should also cover the wire. Or a slip of copper or wire may be laid upon the back, and fastened by a drop or two of sealing-wax; the back is then coated, but care must bo taken that the wax does not get between the connection and the medal, which will prevent deposit. The deposit on this mould goes on instantaneously. When sufficiently thick, it may bo taken off in the same manner as from the wax mould. These moulds may be used several times, if care be taken not to heat them, as they easily melt. The medals obtained from metallic moulds prepared with the turpentine solution have a bright surface, which is not liable to change easily, but if the mould has been prepared with oil or composed of wax or plaster, the metal will either be dark, or will very easily tarnish. For the means of preserving them by bronzing see Nos. 3771, etc..

3691. Precautions on Putting the Moulds into a Solution

3691.     Precautions on Putting the Moulds into a Solution. In putting moulds into the copper solution, the operator is often annoyed by small globules of air adhering to the surface, which either prevent the deposit taking place upon these parts, or, when they are very minute, permit the deposit to grow over them - causing small hollows in the mould, which give a very ugly appearance to the face of the medal. To obviate this, give the mould, when newly put into the solution, two or three shakes, or give the wire attached to it, while the mould is in the solution, a smart tap with a key or knife, or anything convenient; but the most certain means wo have tried, is to moisten the surface with alcohol just previous to putting it into the copper solution. A little practice in these manipulations will soon enable the operator to avoid these annoyances.

3692. Electrotyping on Large Objects

3692.     Electrotyping on Large Objects. When busts or figures, whether of wax or plaster of Paris, are to bo coated with copper, with no other conducting surface than black-lead, it is attended with considerable difficulty to the inexperienced electrotyper. The deposit grows over all the prominent parts, leaving hollow places, such as armpits, neck, etc., without any deposit; and when once missed, it requires 3onsiderable management to get these parts coated, as the coated parts give a sufficient passage for the current of electricity. It is recommended by some electrotypists to take out the bust, and coat the parts deposited upon the wax, to prevent any further deposit on them; but this practice is not good, especially with plaster of Paris, for an electrotype ought never to be taken out till finished. Sometimes the resistance of the hollow parts is occasioned by the solution becoming exhausted from its position in regard to the positive pole. In this case a change of position effects a remedy. It may be remarked that when a bust or any large surface having hollow parts upon it, is to be electrotyped, as many copper connections as possible ought to be made between these parts and the zinc of the battery. Let the connections with the hollow parts be made with the finest wire which can be had, and let the zinc plate in the cell have a large surface compared to the surface of the figure, and the battery be of considerable intensity; if attention is paid to these conditions, the most intricate figures and busts may be covered over in a few hours. Care has to be observed in taking off the connections from the deposit, or the operator may tear off a portion of the deposit; if the wires used are fine, they should be cut off close to the deposited surface.