February 2017 | Dr Gopichand Katragadda

Cast in excellence

Dr Gopichand Katragadda, group chief technology officer, explores how the centuries old tradition of Chola bronze is kept alive at museums around the world, and how the enduring technology survived the last 4,500 years

In January 2016, I had the wonderful opportunity of visiting the conservation areas of the Rijksmuseum, the national museum in Amsterdam. Dr Debasish Bhattacharjee, group director of R&D, Tata Steel, arranged this visit as part of Tata Steel’s engagement with the museum.

After viewing the forensic work done by technologists to uncover hidden secrets in the paintings of master artists such as Johannes Vermeer and the conservation work on ancient clothing of nobility, we visited the metals department. Here we were introduced to a team who had in-depth knowledge of metal-making techniques used in ancient Indian bronzes. They spoke at length about the perfection they observe in the Chola bronzes. The Nataraja on display at the Rijksmuseum, for example, had zero defects even under an X-ray examination.

The making of a masterpiece

  • X-ray studies of the Nataraja at the Rijksmuseum show absolutely no internal defect, an example of metal work at its finest
  • The master artisan explains how a palm leaf is used to create measurements for a model with ideal proportions
  • Beeswax is heated over slow heat while the artisans shape the model into its final form
  • The mould is heated over cow-dung cakes and the heat is contained using gunny bags
  • Five metals are heated in a specially made kiln pot in a rudimentary coke oven
  • The artisan in the background is working with the mould while those in the foreground are working with the molten metal
  • The artisans work in an intuitively coordinated manner to pour the molten metal into the hot mold
  • Skilled artisans shape the sculpture into its final form by chipping, shining and polishing

This article is the story of how the tradition of Chola bronzes continues to be preserved.

In February 2009, I visited Swamimalai in Tamil Nadu. The purpose was to understand the art and craft of making Chola bronzes. C Rajagopalan (Raja), one of my GE colleagues and a fellow traveller on this trip, is the co-author of the monograph, Where Gods Come Alive, a monograph on the bronze icons of South India. Raja had already briefed me on the details of the lost wax casting process, which had been handed down from artisan to artisan from the Chola times and probably even before.

He picked for us to visit Rajan Industries, one of the enterprises producing Chola bronzes today. The master artisan and his disciples took us through the process, which evolved over centuries to the intricate craft that it is today. Royal patronage, during the Chola dynasty (300 AD to 1279 AD), mandating a traditional metal temple deity for village processions (as opposed to the stone deity installed in the temple) led to the perfection of the lost wax casting process.

Here is what I learnt at Rajan Industries:

Model: The artisan uses beeswax to hand-craft a model of the object to be cast for one-time use. The model proportions are based on traditional measures which describe the relative measure of each anatomical part. It was interesting to see how these relative measures are created for ready reference on a coconut palm leaf using folds in a particular order. The relative proportions can vary depending on the nature of the model being cast — there are 10 such variations. A small stove is used to periodically heat the beeswax as the artisan shapes fingers and other features of the model.

Mould: Once the model is ready, local riverbed clay is used to paste the mould around the model. This clay which is available only at the bend of the river Kaveri nearby is very specifically used for its fine grain properties suitable for the moulding process in producing temple-grade sculptures. Metal wires are wrapped around the mould to provide stability.

The mould is then heated resulting in the beeswax melting and running out of the mould through channels. The mould is heated further as it has to reach the temperature of the molten metal which would be poured in. The firing of the mould is done using cow-dung cakes and the temperatures are increased with containment provided using gunny bags.

Metal: Alloy with a five metal (copper, silver, gold, iron and lead) composition is used for temple sculptures. The proportion of gold is small in temple sculptures and gold is not used in decorative sculptures. Scrap is reused and interestingly, metal from older temple idols is used during the melting process. The metal is melted in a kiln pot made from specially sourced clay from Karnataka, which has excellent heat resistance properties suitable to handle molten metals. The fuel used is coke, which is kindled and fired with the aid of a hand-operated air blower. Rudimentary tools are used for holding the kiln pot, mixing the alloy and removing slag during the melting process.

Pouring: Significant expertise comes to play as the kiln pot is lifted and brought to the mould and the metal poured into it. The mould is removed from its firing location and is placed closer to where the metal is being melted. The distance is important as the metal has to be poured with specific timing after it is removed from the flame. The angle of the mould as the metal is being poured is important so that the metal runs down the sides of the mould without splashing. Several hands with rods and tongs play a role in what seems to be an ad hoc and noisy task accomplished with a significant amount of verbal and visual feedback to each other.

Finishing and polishing: The mould with the metal is buried in the ground for several days to allow gradual cooling. Then the mould is removed and broken to reveal the casting. What emerges from the casting process is an unfinished idol with the details still to be incorporated through a manual and skill-based effort. The artisan uses his feet and hands freely to provide the finishing touches of smoothing and polishing; the casting is considered an idol only when the eyes are symbolically ‘opened’.

The Chola bronzes are a showcase of creativity and engineering skills and find a place of pride in major museums around the world. According to recorded history, the Cholas reigned from about 300 AD to 1279 AD. However, the bronze-making tradition might actually date back to 2500 BC, the date of the ‘dancing girl’ statue found in the Indus valley. It was quite amazing to see artisans working in the same manner as maybe our ancestors did some 4,500 years ago.

This article was first published in the January - March 2017 issue of Tata Review. Read the ebook here