3677. To Take Moulds in Plaster

3677.    To Take Moulds in Plaster. If a plaster of Paris mould is to be taken from the metallic medal, the preparation of the medal is the same as described in No. 3676; and when so prepared with the rim of cardboard or tin, get a basin with as much water in it as will be sufficient to make a proper sized mould (a very little experience will enable the operator to know this), then take the finest plaster of Paris and sprinkle it into the water, stirring it till the mixture becomes of the consistence of thick cream ; then pour a small portion upon the face of the medal, and, with a brush similar to that used for oiling it, gently brush the plaster into every part of the surface, which will prevent the formation of air-bubbles; then pour on the remainder of the plaster till it rises to the edge of the rim: if the plaster is good, it will bo ready for taking off in an hour. The mould is then to be placed before a fire, or in an oven, until quite dry, after which it is to be placed, back downwards, in a shallow vessel containing melted wax, not of sufficient depth to flow over the face of the mould, allowing the whole to remain over a slow fire until the wax has penetrated the plaster, and appears upon the face. Having removed it to a cool place to harden, it will soon be ready for electrotyping. Glycerine affords an excellent coating for the interior of plaster moulds, to prevent the melted wax from adhering to the inside of the mould.

3678. To Take Moulds of Plaster from Plaster Models

3678.     To Take Moulds of Plaster from Plaster Models. When a plaster mould is to be taken, the face of the model is prepared differently to that described, in order to prevent the adhesion of the two plasters. The best substance for this purpose is a mixture of soft soap and tallow, universally used by potters for preparing their moulds, and called by them lacquer. It is prepared in the following manner: 1/2 pound soft soap is put into 3 pints clean water, which are set on a clear fire, and kept in agitation by stirring; when the mixture begins to boil, add from 1 to 11/2 ounces tallow, and keep boiling till it is reduced in bulk to about 2 pints, when it is ready for use. The surface of the medal must be washed over with this lacquer, allowing it to absorb as much as it can, when it assumes the appearance of polished marble; it is now prepared with a run of paper, and the mould taken as directed for taking plaster moulds. (See No. 3677 (To Take Moulds in Plaster).) When hardened, they will separate easily. Wetting the plaster model with a solution of soap before taking the cast will do, or, if the plaster model has been saturated with oil or milk, it has only to be moistened with sweet oil the same as a metal model.

3679. To Take Moulds of Fusible Alloy from Plaster Models

3679.      To Take Moulds of Fusible Alloy from Plaster Models. If a mould of fusible metal be required from a plaster model, the plaster may be saturated either with boiled oil (see No. 3676 (To Take Wax Moulds from Plaster)), or the soap and tallow lacquer (see No. 3678 (To Take Moulds of Plaster from Plaster Models)), and the mould taken in the same manner as from a metallic medal. (See No. 3677 (To Take Moulds in Plaster).)