54 ELECTROTYPE PROCESSES. 



the wax would adhere to it, and, being thus prevented from shrink- 

 ing, which it always does a little, would be liable to crack. Put the 

 medal and wax in a cool place, and in about an hour the two will 

 separate easily. When they adhere, the cause is either that too 

 little oil has been used, or that the wax was poured on too hot. 



Rosin with Wax. Rosin has been recommended as a mixture 

 with wax ; mixtures of which, in various proportions, we have used 

 with success : but when often used, decomposition, or some change 

 takes place, which makes the mixture granular and flexible, render- 

 ing it less useful for taking moulds. When rosin 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. 



Moulds in piaster. If a plaster of Paris mould is to be taken 

 from the metallic medal, the preparation of the medal is the same 

 as described above ; and when so prepared with the rim of card- 

 board 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 be 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 elec- 

 trotyping. If the mould is large and the plaster thick, the wax ma}'- 

 be put upon the surface, and only as much as will penetrate a small 

 way into the plaster. In both these instances the wax used is gen- 

 erally lost, and there is always liability of the copper solution passing 

 through, and causing what is termed surface deposit, making the face 

 of the medal rough. We may remark that, although occasionally 

 there may be a very good electrotype obtained from a plaster mould, 

 still they are in general very inferior ; as the saturating of the plaster 

 has a tendency to blunt the impression, and the wax used for the 

 purpose of saturation becomes expensive. It may be partiaDy 

 recovered by boiling the plaster in water : the wax melts out, and is 

 obtained when the water cools. Plaster should not be- used for 

 moulds where wax can be employed, being neither so good nor so 



