Permanent moulds made from stone

Permanent moulds are re-usable, quite the contrary is true for clay or sand moulds., which can be used only once. The advantge of permanent moulds is obvious: without much effort you can create a whole lot orf castings of the same object. The disadvantage are:

only simple objects can be produced with stone moulds, you have to be extra careful to avoid any undercuts, as to ensure demoulding.
Another slight draw back is the increased amount of time and effort suring mould production.

Here you can see one half of a mould for a sickle; the second half is a flat stone slab without incisions, since the sickle has only a flat back-side. These halves are sometimes referred to as blind halves. Stone moulds are fine way to go if you wish to cast simple shapes, like axes, knifes, daggers, sickles, swords (that is, it is by no means easy to cast swords or rapirs due to the long narrow shape)

Permanent moulds with cores

Craftsmen of the bronze age have been very inventive and thus found a way to cast more complicated objects, for example spear-heads with sockets. Usually a socket cannot be cast hollow in a mould consiting of two halves. You would have to create a socket by means of drilling.

They discovered the use of a core. A core is a small piece of refractory material, which is placed in the mould and creates a cavity in the cast (see image). The core forms the insides of the cavity and has to be removed after casting. Cores can be of many materials and there are both, permanent and lost cores. Cores of clay, sand or stone have to absolutey dry before casting. Otherwise your mould might explode due to a massive development of steam. In later times cores were even made of metal.

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