WAX CASTINGS AND GUTTA-PERCHA MOULDS. 9 



with a sharp knife and lay one half flat on the table and pour 

 over it plaster slip just about to set, until it is coated about an 

 inch thick; or fill a well-greased cup with slip and then press 

 into it the half lemon until the flat cut surface is level with the 

 slip and the mouth of the cup. In this way you will ultimately 

 obtain a plaster mould of one half of the lemon. Now do exactly 

 the same with the other half, and when the two moulds are 

 thoroughly set, apply them together and fasten them by tying or 

 by a piece of wire bent into a clip (fig. 9), so that the hollow parts 

 of each half mould coincide. Scoop 

 out a small hole in the plaster in 

 order to pour in melted wax and let 

 out air, but before thus filling the 

 mould, press a little soft plaster (slip 

 just solidifying) into the interstices 

 where the two half moulds meet, so as Yl & 9 - Wire cli P- 



to fill up the crevice and prevent the wax running out thereat. 

 The softened surface-layer of a piece of common yellow soap 

 soaked in water will also serve conveniently as a " caulking " to 

 make the mould tight at this part. The wax should not be too hot, 

 just enough to enable it to flow readily into the mould and not to 

 set before it has filled it up. When the wax is cold the plaster 

 moulds are carefully separated and a wax model of the lemon 

 obtained; this requires a little paring and trimming at the line 

 where the two halves meet and the part where the wax was 

 poured in, after which it may, if required, be tinted yellow to 

 render it a perfect facsimile of the original lemon. The plaster 

 moulds can be used over and over again for making additional 

 wax models, but care must be taken to damp the plaster so 

 as to prevent the wax sticking to it. Fruit of all kinds and 

 many other solid objects may be moulded in precisely the same 

 way. 



Expt. 6. To take Impressions in Gutta-Percha. Gutta-percha 

 is a very convenient material for taking casts, more especially 

 those intended to be employed in turn as moulds so as to produce 

 replicas of the original object. A sufficiently large piece is well 

 softened in very hot water, and well rolled and kneaded in 

 the hands, to which it will not stick if they are previously 

 thoroughly wet. The coin, &c., to be copied is placed on a flat 

 table with wetted surface, and the plastic gutta-percha pressed 

 down on to it thoroughly, and finally covered with a plate or flat 

 wet board with a weight on, and allowed to stand. After some 

 time the gutta-percha will have cooled and set, when the coin can 

 readily be removed from it, the mould being somewhat elastic ; but 



