3672. To Obtain a Copper Mould of a Coin

3672. To Obtain a Copper Mould of a Coin. A fine copper wire must be put round the edge of the coin and fastened by twisting. Then cover the back part, and the wire, upon which the deposit is not required, with bees' wax or tallow, or, what is better, imbed the back of the coin in gutta percha. Have the fore part or face well cleaned, and the surface moistened with sweet oil, by a camel's-hair pencil, and then cleaned off by a silk cloth, till the surface appears dry; or, instead of oil, the surface may be brushed over with black lead, which will impart to it a bronze appearance. The use of the oil or black lead is to prevent the deposit adhering to the face of the coin. The coin is now ready to bo subjected to the single cell process (see No. 3G69), by which means a perfect counterpart or mould of the coin is obtained. This mould may next be treated exactly as described for obtaining it from the original coin, and the deposit from it will be a fac-simile of one side of the coin. With care, any number of duplicates may be taken from this mould, if it be properly coated.

3673. Coating for Copper Moulds

3673.      Coating for Copper Moulds. Take a gill of rectified spirits of turpentine, and add to it about the size of an ordinary pea of bees' wax. "When this is dissolved, wet over the surface of the mould with it, and then allow it to dry: the mould is then ready to put into the solution. Medals taken from moulds so prepared retain their beautifully bright color for a long time. But when fine line engravings are to be coated, the little wax dissolved in the turpentine may be objectionable; so also is black lead, for both have a tendency to fill up the fine lines. In this case, let the turpentine wash be wiped off with a silk handkerchief, instead of drying it; but for ordinary medals this objection will scarcely apply.

3674. Preparation of Wax for Taking Moulds

3674.   Preparation of Wax for Taking Moulds. Whether the bees' wax have stearine in it or not, it is best to prepare it in the following manner: Put some common virgin wax into an earthenware pot or pipkin, and place it over a slow fire; and when it is all melted, stir into it a little white lead (flake white), or black lead (plumbago), say about 1 ounce white lead to the pound of wax; this mixture tends to prevent the mould from cracking in the cooling, and from floating in the solution; the mixture should be re-melted two or three times before using it for the first time. Resin has been recommended as a mixture with wax; mixtures of which, in various proportions, have been used with success ; but when often used, decomposition or some change takes place, which makes the mixture granular and flexible, rendering it less useful for taking moulds. When resin is used, the mixture, when first melted, should be boiled, or nearly so, and kept at that heat until effervescence ceases; it is then to be poured out upon a flat plate to cool, after which it may be used as described.