All moulds, whether for steel, iron or brass, must fulfill the following general requirements, viz.:

(1) They must be made so that the pattern can be removed readily therefrom.

(2) Not only must an opening be made in the sand for pouring metal into the mould, but a riser hole must lead upward through the sand from each of the high parts of the mould cavity. This serves (a) to keep air from being imprisoned in the mould when metal is poured in; (b) to allow for loose sand and scum on the metal to float out, and (c) to provide a bulk of hot metal to "feed" the casting as it shrinks in solidifying.

(3) A mould must resist burning and crumbling when filled with molten metal, and must resist bursting from the static pressure of the metal.

The requisite qualities of sand for moulds will be mentioned later.