Ancient Casting Practice

The majority of the surviving relics of early copper work are in cast form, an art which the Egyptians quickly brought to a high state of perfection. It is less easy to cast copper than bronze; but once they had learned to alloy the metal deliberately with tin, and frequently also with a little lead, the operation became much easier. The melt flow was improved, and thereafter there was no limit to their fertility of invention. In this connexion, it must be remembered that the abundant remains, which the world possesses today, are but a fraction of what once existed in Egypt, the rest having been stolen or melted down and recast into other forms.

As the fashioning and baking of clay into useful and beautiful objects was one of man's earliest discoveries and indeed may be said to come almost naturally to human fingers, clay moulds were probably employed for the earliest metal castings; a few wooden ones are also known. Open moulds no doubt came first; but as these can only produce articles that are flat on one face, the use of closed moulds must have followed soon afterwards. To cast copper successfully calls for special precautions, as it may give rise to sulphurous gases; molten copper also tends to pick up oxygen which can create unsound castings. Special openings or risers in the mould are therefore necessary, both for pouring the metal and to permit the escape of dirt and gases. The ancient coppersmith, however, was well aware of these difficulties and became very successful in overcoming them.

When a little tin or lead is added, even accidental amounts like i per cent, the production of sound castings becomes much easier; and this must have hastened the development of bronze as a definite alloy. Eventually their techniques became so sophisticated that bowls of almost incredible thinness, yet still perfect, were cast in this metal. At an early date great skill was acquired in fashioning double stone moulds which allowed repetition work. Sand castings, however, seem to have been less common. ⁽³⁾

By one or other of these processes, all manner of things came into existence-palstaves, axes, bowls, tools of many kinds, weapons, celts, figurines, large vases and sacred vessels.

The Egyptians are commonly credited with inventing the lost wax or cire perdue method of casting metal. This was known too in China, but apparently only at a much later date. A. Lucas ⁽⁴⁾ describes the process:

'A model in beeswax was made of the object to be cast. This was coated with a suitable material to form the mould, probably clay or a clay mixture, and embedded in sand or earth which acted merely as a support. The hole was then heated and the wax melted and either burnt away or ran out through the hole or holes provided to receive the molten metal; the mould became hard and rigid, and ready for use. Then the molten metal was poured in and allowed to cool, after which the mould was broken away and the object given the necessary finishing touches with a chisel.'

Cire perdue provided solid castings upon which a great refinement of ornament or detail could be worked. Hollow castings were also made: these required some kind of core which was held in place either without support or by wires or other devices.

Another casting method, ideal for repetition work, was to fashion clay around an article and then remove the coating in sections. These were next thinly coated with wax and carefully reassembled. Hot wax was poured in and the mould rotated until the required thickness of solidified wax was obtained upon the inner walls. The removal of the mould left a complete wax model which could then be embedded in a suitable moulding material for treatment as described earlier. The necessary air-vents and runners for the metal were fashioned in wax whilst additional ornamentation was frequently applied by means of dies.

By these various methods, metal shells and patterns of extreme delicacy were frequently obtained.

The process of beating thin copper sheets against a former, with or without the addition of special ornamentation or engraving, was also used by the ancient coppersmith to make a large variety of artistic objects.