Cast-iron is melted in a furnace known as a cupola, but for small quantities of softer metals, crucibles of fireclay or plumbago are made use of. For the softest metals and alloys, a ladle, heated on an open forge fire may be found quite sufficient, if large enough to contain the quantity. In any case, the utmost caution must, at all times, be taken, so as to prevent accidents, which often assume a very dangerous form. Ladles used for molten metal must be carefully prepared and made perfectly dry. This is ensured by covering the inside with clay, which has to be thoroughly dried and smoked. After everything is ready, a sufficient quantity of metal is run into the ladle, and cautiously poured into the mould, until it appears at the top of the ingate. In a short time, in the majority of cases, the metal will set or get into a solid state, soon after which it may be removed from the mould and exposed to the air. If there is danger of fracture, arising from unequal speed of contraction in the different parts, it is often advisable to expose only those least likely to cool quickly, and so, if possible, produce a sound casting. Sometimes the castings are left in the sand all night, so as to cool slowly. Little more remains to be done in the foundry, except to remove any surplus parts of the metal, or to drive out the cores employed in different parts of the construction.