3680. Copper Moulds from Plaster

3680.    Copper Moulds from Plaster. Many electro-metallurgists prefer taking a mould in copper when the medal is of plaster of Paris. This is done by the electrotype process (see No. 3671 (Electrotyping with a Battery)); the plaster model is saturated with wax over a slow fire, as already detailed, and then prepared for taking an electrotype in the usual manner (See No. 3672 (To Obtain a Copper Mould of a Coin), etc..) We need hardly mention that the model in this case is destroyed; but, notwithstanding, in the case of plaster models, to take a copper mould is the most preferable, as it may be repaired in case of slight defect, and it may be used over and over again without deterioration. When an electrotype is required of a model that is undercut, or of a bust or figure, the process which we have described will not answer, as the mould cannot separate from the model. In such circumstances the general method of proceeding is to part the mould in separate pieces, and then join these together. The material used for this purpose is plaster of Paris. The operation, however, to be well done, requires a person of considerable experience.

3681. To Take Moulds in Gutta-

3681.      To Take Moulds in Gutta-. Percha. Gutta - percha, as a material for moulding, serves the purpose most admirably. The method adopted for taking moulds is to heat the gutta-percha in boiling water, or in a chamber heated to the temperature of boiling water, which makes it soft and pliable. The medal is fitted with a metallic rim, or placed in the bottom of a metal saucer with a cylindrical rim a little larger than the medal; the medal being placed back down, a quantity of gutta-percha is pressed into the saucer, and as much added as will cause it to stand above the edge of the rim. It is now placed in a common copying-press and kept under pressure until it is quite cold and hard. The impressions taken this way are generally very fine. When the medal is not deep cut a less pressure may suffice, but when the pressure is too little the impression will be blunt. Gutta-percha takes a coating of black lead readily, and the deposit goes over it easily. A mixture of gutta-percha and marine glue has been recommended for moulds as superior to gutta-percha alone. This method of moulding by pressure is adopted, in principle, by printers, for making electrotype plates from type and engravings, employing sheets of prepared wax, at a temperature which gives it the proper consistency.

3682. To Mould the Face of a Person in Wax

3682.    To Mould the Face of a Person in Wax. Take 1 pound new wax, 1/8 pound resin, melt them at a slow fire, let them cool till you can endure some of it on your hand without burning it; then, having oiled the face with olive oil, and covered the hair of the eye-lids and eye-brows with paste, with a brush nimbly cover the face about the thickness of a quarter of a dollar, being careful not to stop the nostrils, and that the person does not close his eyes firmly enough to wrinkle his face, because that will render the face deformed. Take the wax off gently, and strengthen it with clay on the back, that it may not give way. After this manner you may cast all sorts of faces; laughing, weeping, or wry faces; also fruits or anything else, dividing the mould into two pieces with a warm knife; then fortify them with clay and join them together.