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.
Crucibles vary in size, shape, and composition, according to their destined uses. The so-called "plumbago" crucibles, made of graphite, are dearest but most durable. The cheaper kinds are made of pipeclay. They are charged with the metal to be melted, and placed in a sufficiently strong fire, such as that obtainable on a smith's forge. For considerable quantities of metal, the crucible is dispensed with, and the melting is conducted in a blast furnace.
The ironfounders' pot is illustrated in Fig. 6, and consists of an iron pot supported by a handle which is single at one end and double at the other. In very small operations this may be replaced by an iron ladle.
Very small articles can be cast in moulds made of stone, brick, or iron, the interior surfaces being first coated with a "facing" of soot, by holding over a smoky flame, to prevent adhesion of the metal when poured in. But for general casting operations, recourse is had to sand packed into "flasks" or "boxes" surrounding the pattern. The flask resembles a box, without top or bottom, and made in 2 sections, so that the top half may be lifted away from the bottom half, or joined to it by bolts to form the whole. Fig. 7 illustrates the upper "side" of a flask, in which a is a handle, b are the holes by which the metal is poured in, and c are lugs carrying pins which pass through corresponding holes in similar lugs on the bottom side. The pattern being placed in a flask of suitable size, the space intervening on all sides between the pattern and the flask is packed in with sand, which, to be of suitable quality, must retain a ball shape on being squeezed in the hand, and exhibit an impression of the lines and inequalities of the skin surface that pressed it. The finest quality of sand is placed next the pattern, and the surface of the latter is dusted with dry "parting sand," to prevent adhesion.
The packing of the sand is performed by the aid of a moulding-trowel (Fig. 8), which consists of a thin steel blade in a wooden handle; a moulding-wire (Fig. 9), useful or smoothing corners and removing dirt from the mould; and a stamper (Fig. 10), or pestle of hard wood or iron. Runner sticks of smooth tapering form are inserted in the holes b of the flask, to make feeding ways for the metal. When the impress of the pattern has been properly taken in the mould, the pattern is removed, and the top and bottom sides of the flask are joined, enclosed on the open sides by thick boards, and transferred to a clamp (2 boards joined by adjustable screws) to prevent its giving way under the sudden and considerable pressure produced by the weight of metal poured in, and expansive tendency of the gases generated.