This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
The bust in wax, having been looked over and corrected by the artist, is now placed in the hands of the founder, who begins by building a layer of fire-bricks of the size required for the object that is to be cast; this layer, for a bust, may be 3 ft. by 2 ft. 4. in. and 9 in. in height above the floor of the atelier. When ready the wax bust is placed upon it on its pedestal of "potin," and firmly fixed to the brick layer or base. The next operation is one of considerable delicacy, namely, the placing of the runners or channels to enable the liquid bronze to flow through and fill up the vacant space left by the melted wax, and the vents, which are other channels for the escape of the air and gas driven out of the hollow by the force of the liquid metal.
For a bust the placing of these channels is not difficult, but when a complicated work - a group or a large bas-relief - has to be prepared for casting, the proper position of these channels requires considerable study, for if one of them should be badly placed it would compromise the success of the casting.
In order to make a runner for the bust in question, a stick of wax is used 2 ft. long with a diameter of 1 3/4 in., one end of which is cut or flattened into the shape of the mouthpiece of a whistle; the other end is considerably thickened by the addition of wax until it has the form of a funnel; it is then bent into the form of a double siphon with the 2 parallel branches considerably lengthened. Having thus prepared the runner, in order to fix it, 3 or 4 thin iron pins are driven, in a straight line, at a distance from each other of 1/2 in., into one shoulder of the bust, from which they are allowed to project about 1 or 1 1/2 in.; upon these is pressed the flattened end of the runner, and the joint where it touches the shoulder is then closed with wax, which is melted with a heated tool, thus increasing the solidity of the joints. The vent, which is fastened in the same way on the other shoulder, is a simple straight stick of wax, thinner than that of the runner, also with the flattened end touching the shoulder.
If from any cause the runner and the vent are not firm in their positions, another iron pin is driven into the top of the head of the bust, and the runner and vent are fastened to it with packthread.
The founder has now before him the bust, surmounted by the runner and the vent rising from the shoulders to the summit of the head, like little chimneys, to the height of 6-8 in.; he then proceeds to drive a number of iron pins all over the surface of the bust, through the wax, into the core, the object of which is to maintain the core in its place; these pins must project one-half their length from the surface of the bust.