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To Use Metal Moulds

The mould in fusible alloy does not require to be together, and boil the cast until it will not black-leaded, but the surface to be electroabsorb any more; when cold, get some good typed must be prepared with turpentine, &c., black lead and cover the cast entirely, not (see No. 3673), and the back and edge must thick, but a bright surface. (See No. 3389.) be protected by a coating of wax or other

3689. To Prepare Non-Metallic non-conducting material; it may be connect- Moulds to Receive Deposit. Were any ed with the zinc pole by putting a wire round of the plaster or wax moulds, described above, its edge previous to laying on the non-conattached to the zinc and immersed in the cop- ducting substance, such as tallow or wax, per solution in the same manner as described which should also cover the wire. Or a slip in No. 3369, no deposit would be obtained, of copper or wire may be laid upon the back, because neither the plaster nor the wax is a and fastened by a drop or two of sealing-wax; conductor of electricity. Some substance the back is then coated, but care must be must now be applied to the surface in order taken that the wax does not get between the to give it conducting power. There are seve- connection and the medal, which will prevent ral ways of communicating this property, but deposit. The deposit on this mould goes on the best and most simple for the articles under instantaneously. When sufficiently thick, it consideration is to apply common black lead may be taken off in the same manner as from (carburet of iron) in the following manner:

A copper wire is put round the edge of the medal, or, if wax moulds are used, a thin slip of copper may be inserted into the edge of the mould-or, being slightly heated and laid 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, upon the back, the two will adhere. A fine which is not liable to change easily, but if the brush is now taken (a small hat brush is very mould has been prepared with oil or composed suitable) and dipped into fine black lead, and of wax or plaster, the metal will either be brushed over the surface of the metal. The dark, or will very easily tarnish. For the brushing is to be continued until all the face means of preserving them by bronzing see round to the wire upon the edge, or slip of Nos. 3771, &c. copper forming connection, has a complete 3691. Precautions on Putting the metallic lustre. A bright polish is neces- Moulds into a Solution. In putting sary to obtain a quick and good deposit. moulds into the copper solution, the operator In brushing on the black lead, care should is often annoyed by small globules of air adbe taken not to allow any to go upon the back or beyond the copper connection, or the deposit will follow it, and so cause a loss of copper, and make the mould more difficult to separate from the deposit; being, as it were, incased. When the face of the mould is properly black-leaded, the copper wire connected with it is attached to the zinc plate in the porous cell, and the mould immersed in the copper solution; the deposit will immediately begin upon the copper connection, and will soon spread over every part, completely covering the black-lead surface. When the deposit is considered sufficiently thick for removing-which, in ordinary circumstances, will require from 1 to 3 days-the medal is taken out of the solution, and washed in cold hering 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 we 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 Obwater, and the connection is taken off. If jects. When busts or figures, whether of the deposit has not gone far over the edge of wax or plaster of Paris, are to be coated with the mould, the two may be separated by a copper, with no other conducting surface than gentle pull; if otherwise, the superfluous black-lead, it is attended with considerable deposit must be eased off, and if care be taken difficulty to the inexperienced electrotyper. the wax may be fit to use over again; but The deposit grows over all the prominent when the mould is plaster of Paris, however parts, leaving hollow places, such as armpits, well it may be saturated with wax, it is sel- neck, etc., without any deposit; and when dom in a condition to use again. If the once missed, it requires considerable manageplaster mould be large and thick, it is advisa- ment to get these parts coated, as the coated ble to coat the back with wax or tallow, parts give a sufficient passage for the current which is done by brushing it over with either of electricity. It is recommended by some substance in a melted state; the mould, being electrotypists to take out the bust, and coat . the parts deposited upon the wax, to prevent any of the electrical apparatus at present emany further deposit on them; but this practice ployed for coating articles with metal. The is not good, especially with plaster of Paris, solution intended to be used is prepared by for an electrotype ought never to be taken dissolving 4 ounces silver in nitric acid, and out till finished. Sometimes the resistance afterwards diluting the same with 12 gallons of the hollow parts is occasioned by the solu- water; the gold solution is formed by dissolvtion becoming exhausted from its position in ing 1 ounce gold in nitro-muriatic acid (aqua regard to the positive pole. In this case a regia), and then diluting it with 10 gallons change of position effects a remedy. It may water. The solutions of silver and gold, prebe 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. pared as above, will last for a long time, and serve for a great many articles. When it is convenient it is best to use both solutions.

The connecting wire should first be attached to the article to be coated, before being dipped into the phosphorus solution, but connected at such parts as will not hurt the appearance of the object by leaving a mark when it is taken off. Care should be taken not to touch the article with the hands after it is dipped into the solution. The object supported by the connections is immersed in the phosphorus solution, where it remains for two or three minutes. When taken out it is dipped into the silver solution, and, as soon as the surface becomes black, having the appearance of a piece of black china, it is to be dipped several times in distilled water, and then immersed in the solution of gold about three minutes;