Also known as cire perdue in French, the lost-wax process or “investment casting” is one of the oldest known techniques for making sculptures out of metal. The process is so named because it centres on the removal of a wax core (due to its low melting point) for the preparation of a mould. An image is first modelled in wax and then covered with clay, which is then fired. The wax melts out through an opening while the clay sets to form a hard terracotta mould. Molten metal is poured into this mould to take the form of the original wax image upon setting, revealed as the terracotta casing is finally removed. Archaeological evidence suggests that the technique saw its earliest applications between the fifth and second millennia BCE in the region between the Indo-Gangetic plains of South Asia and the Aegean in Europe. In subsequent millennia, it continued to be used in the region as well as in China, the British Isles, North and West Africa, Central and South America and other parts of Europe. Apart from material evidence attesting to its use, there are indirect and direct references to lost-wax casting in texts such as Pliny the Elder’s first century CE treatise Natural History, the twelfth- and sixteenth-century texts of the Shilpashastras; and the mediaeval and early modern European texts Pirotechnia and Treatise on Sculpture.

Though its exact origin is unknown, lost-wax casting is thought to have first developed in and around the Iranian plateau. Some of the oldest artefacts made using the lost-wax process — a set of copper-alloy amulets — have been found in Mehrgarh in Balochistan (in present-day Pakistan), and were probably produced before 3000 BCE. Excavations at the Indus Valley Civilisation sites of Harappa, Chanhu-daro and Mohenjo-daro in Pakistan have revealed more lost-wax bronze figures, the most iconic example of which is the Dancing Girl statuette, dated to 2300–1750 BCE. The continuing use of the technique in South Asia is attested to by a group of bronze images from Kolhapur, Maharashtra, believed to be from the second century CE; fragmentary Buddha icons from Amaravati, dated to the third century CE; and Buddha sculptures from the Gangetic Plains in the fourth–fifth centuries CE, by which point it appears that the technique was being further developed and refined. The Sultanganj Buddha, dated to between the sixth and eighth centuries CE, is one of the largest known examples of a sculpture produced using the technique, weighing around 500 kilogrammes.The most well-known and sophisticated Indian examples of lost-wax sculptures are Chola bronze sculptures, especially of Nataraja, produced through the tenth–thirteenth centuries.

Much of the mediaeval metalwork that used this technique appears to have referred to texts which detailed the technical process needed, as well as the dimensions, proportions, iconography and dress and treatment of the sculptures produced. Most important among these are the Manasara Shilpashastram, believed to have been compiled towards the end of the first millennium CE, the Manasollasa of the twelfth century, and the Shilparatna of the sixteenth century.

The method of the lost-wax process as described in the Shilpashastras consists of a series of steps. It begins with making a model of the figure (or parts of it) using a mixture of beeswax (madhuchishta), dammar gum and groundnut oil and then encasing it in multiple layers of clay, called the ‘investment’. This is then dried and fired, which causes the clay to harden to terracotta, while the wax inside melts and flows out through runners. Following this, metals are melted together and poured into the mould, which is then allowed to cool and set naturally. Finally, the cast figure is revealed by breaking the terracotta casing, usually beginning with the head and then the body. This is often carried out with much ceremony because of the religious nature of the objects being created. The detailing, buffing and polishing are done by hand with simple tools and local ingredients such as soapnut and tamarind.

The texts suggest that the casting metal should be a combination of copper, silver, gold, lead and zinc, known as panchaloha (“five metals”), considered auspicious. The alloy is also durable, corrosion-resistant, malleable and lustrous, which makes it particularly suitable for casting idols and ritual items. Variations of the alloy, usually with other metals substituting gold and silver, are also used depending on the resources locally available and the properties desired in the finished product.

This method of metal casting is still used for producing bronze sculptures in certain parts of south, central and east India. In south India, it is used for idol making by the sthapathy community of Swamimalai (Thanjavur district) — who still rigorously follow the ancient texts in every aspect of creating the solid figures. The lost-wax metal craft, although practised only by a few communities, has in recent years seen a revival through institutional and government interventions that have made it commercially viable for practitioners and more accessible to urban consumers.