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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); 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, &c.) We need hardly mention that the model in this case is destroyed; but, notboard or tin, get a basin with as much water withstanding, in the case of plaster models, in it as will be sufficient to make a proper to take a copper mould is the most preferable, sized mould (a very little experience will as it may be repaired in case of slight defect, enable the operator to know this), then take and it may be used over and over again withthe finest plaster of Paris and sprinkle it into out deterioration. When an electrotype is the water, stirring it till the mixture becomes required of a model that is undercut, or of a of the consistence of thick cream; then pour bust or figure, the process which we have a small portion upon the face of the medal, described will not answer, as the mould canand, with a brush similar to that used for oil- not separate from the model. In such ciring it, gently brush the plaster into every cumstances the general method of proceeding part of the surface, which will prevent the is to part the mould in separate pieces, and formation of air-bubbles; then pour on the then join these together. The material used remainder of the plaster till it rises to the for this purpose is plaster of Paris. The edge of the rim: if the plaster is good, it will operation, however, to be well done, requires be ready for taking off in an hour. The a person of considerable experience. mould is then to be placed before a fire, or in 3681. Τοo Take Moulds in Guttaan oven, until quite dry, after which it is to Percha. Gutta-percha, as a material for be placed, back downwards, in a shallow ves- moulding, serves the purpose most admirably. sel containing melted wax, not of sufficient The method adopted for taking moulds is to depth to flow over the face of the mould, al- heat the gutta-percha in boiling water, or in a lowing the whole to remain over a slow fire chamber heated to the temperature of boiling until the wax has penetrated the plaster, and water, which makes it soft and pliable. The appears upon the face. Having removed it to medal is fitted with a metallic rim, or placed a cool place to harden, it will soon be ready in the bottom of a metal saucer with a cylinfor electrotyping. Glycerine affords an ex- drical rim a little larger than the medal; the cellent coating for the interior of plaster medal being placed back down, a quantity (f moulds, to prevent the melted wax from gutta-percha is pressed into the saucer, and a adhering to the inside of the mould. much added as will cause it to stand above the edge of the rim. It is now placed in a so under the edge. The inside of this vessel common copying-press and kept under pres- is oiled, a piece of stout paper is pasted on sure until it is quite cold and hard. The im- the bottom of the bust to prevent the fluid pressions taken this way are generally very mixture from going inside, and if it is comfine. When the medal is not deep cut a less posed of plaster, sand is put inside to prevent pressure may suffice, but when the pressure it from floating. It is next completely is too little the impression will be blunt. drenched in oil and placed upright in the ves- Gutta-percha takes a coating of black lead sel. This done, the melted mixture of glue readily, and the deposit goes over it easily. and molasses is poured in till the bust is sub- A mixture of gutta-percha and marine glue merged to the depth of an inch. The whole 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. must stand for at least 24 hours, till it is perfectly cool throughout-after which it is taken out by inverting the vessel upon a table, when, of course, the bottom of the bust is presented bare. The mould is now cut by means of a sharp knife, from the bottom up the back of the bust to the front of the head. It is next 3682. Το Mould the Face of a Person held open by the operator, when an assistant in Wax. Take 1 pound new wax, 1/8 pound lifts out the bust and the mould is allowed to resin, melt them at a slow fire, let them cool re-close. A piece of brown paper is tied round till you can endure some of it on your hand it to keep it firm. The operator has now a without burning it; then, having oiled the complete mould of the bust in one piece; but face with olive oil, and covered the hair of he cannot treat it like wax moulds, as its subthe eye-lids and eye-brows with paste, with a stance is soluble in water, and would be debrush 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.