Lost-wax metal casting
This technique represents possibility of creating an exact copy of original; or in case of producing a completely new object, an ability to create a complex one with many details. It has been used for thousands of years BC (more about the history in the last paragraph) to this day for gold, silver, bronze as well as brass. Today we can achieve faithful replicas of archaeological finds with it.
In case of casting a copy of original, first a negative of a given object is formed, using silicone, which accurately reproduces original‘s shape (on the top of it, solid layer (e.g. stucco, gypsum) may yet come to fix it). This silicone mould is then filled with liquid wax (beeswax or paraffin, eg. hard wax for modellers), which provides basis for casting; it is possible to retouch it before proceeding further. An alternative is to create a wax model by hand. We’ll see how traditional practices will change due to development of 3D printers and computer modeling. Important is not to forget to create risers (also from wax) for the escape of air when the metal is poured in so the product is not deformed by an air pocket (liquid metal reaches in these channels too so it must be carefully removed at the end); alternative is a modern technique of vacuum casting. A mould is then created by wrapping around the wax model using specific mixtures similar to cast (gypsum), in the history it was a mixture of fine clay, chalk and organic straw and similar materials. The refractory mould filled with wax is inserted into furnace where at temperature about 100° C the wax is “lost” from inside (is flows out and its residue evaporates) which frees space for the metal casting. It is necessary to perfectly dry the mould. The actual metal casting takes place at temperatures at hundreds of degrees according to a specific metal. After cooling down, the mould covering the cast is broken (someone puts still hot cast into cold water so the mould cracks). Purification, grinding, respectively patina and decorating follow.
At the time around 4000 BC, independently in several areas (present-day Iran, Syria, Israel, Anatolia, Thailand), the field of metallurgy began to develop. The first attempts were casting objects of copper into forms made of stone or less frequently of clay or loam, later two-pieces moulds. Sometime in this millennium, possibly also in several areas independently, someone came with an idea of wrapping an object modeled from wax with some clay and then to heat it in order to strengthen the clay mould and secondly, to get the wax out. Metal poured into the mould then received the same details as the wax template had; it was a truly revolutionary method, since carving in stone by far doesn’t allow such a play with the details and objects made of clay were easily broken. Besides, it used a material – wax – that had been known for a long time and widely used. Some of the oldest findings are figures of recumbent animals that were part of cylindrical seals made of limestone or magnesite (about 3500 BC). Further there are findings of large pins for clothing, often also with animal motive decorations. Great development of the method is recorded in Mesopotamia, in the second half of the 3rd millennium it significantly expanded throughout the Middle East and the Aegean Sea. Most of the objects found by archaeologists were in royal tombs or in religious objects like temples (objects related to religion). The first written mention of this method is from 1789 BC (from Babylonia) – it is an official document confirming handing over of wax for purpose of making a key to the temple. In Central Europe, the method caught on around 2000 BC; although there is a possibility that it was invented independently (the use of copper in this region was already known for about 2000 years), more likely the knowledge was brought there by trade routes along the Danube. From there it spreaded further north. In Egypt, metalworking was rather conservative for a long time; rapid development started with the New Kingdom (from 1559 BC). Metal casting using this method was frequently used by the Phoenicians (bronze, gold). Also the Scythians used the method perfectly for objects with animal motifs, often made of gold. The largest collection of Scythian metallic art found in Siberia is in St. Petersburg Hermitage Museum; Scythian influenced Europe as well which is documented by findings. The method was transferred to China around 400 BC. In India, the method has been particularly used for the Buddha statues. The Spaniards in the New World encountered widely developed metal casting using the lost wax. Similarly, although at a lower level, the method was used in West Africa, where it was observed by the Portuguese. The Etruscans reached exceptional levels of utilization of lost wax casting. The Celts developed the method further; largely under the influence of the Southern nations, respectively their wine – the Celts tried to emulate and improve southern vessels for storing and serving wine. Extraordinary testament of their level of use of this method are Celtic torcs (torques). Celtic craft has survived for centuries, particularly in Ireland. The Romans also knew and used the method. In the early Middle Ages, we have evidence especially in the form of jewelry and brooches. Later, this way of metal casting was developed in monasteries, which also meant widening of production of religious objects; German Benedictine monk Theophilus, being himself a practicing caster, is an author of the first written description of details of the production process (1st half of 12th century). The Italian Renaissance brought fashion of human statuettes that became subject of diplomatic gifts or private collections; as a novelty also portrait medals appeared (head or bust of a particular person), inspired by ancient coins. In the following centuries, the method continued to be used for production of small bronze objects, gold jewelry and more and more for sculptures. In the 20th century, modernization facilitated the production process.