Zinc was largely used in manufacturing brass. Brass, an alloy of zinc and copper, is known for a long time and can be produced accidentally as has been reported from China and West Asia. In India also there are examples of brass from Lothal and Atranjikhera in 3rd and 2nd Millennia contexts. The ancient Persians attempted to reduce zinc oxide in an open furnace but they failed.
Zinc is a difficult and enigmatic metal. In the earliest cementation process
finely divided copper fragments were mixed with roasted zinc ore (oxide) and
charcoal (a reducing agent), and heated to 1000°C in a sealed crucible.
The zinc vapour thus formed dissolved into the copper fragments yielding a
poor quality brass, zinc percentage of which could not be easily controlled.
Reduction around 1000°C is crucially important as below 950°C no zinc is produced. If the temperature was raised above 1083°C, copper melted and flowed down to the bottom of the crucible. Because of such properties, pure zinc smelting was mastered so late.
It has been demonstrated experimentally that brass produced by the cementation process could not contain more than 28 percent zinc. For producing higher zinc content brass, one requires pure zinc to be mixed with copper, which could have been possible only after discovery of zinc as a separate metal and its preparation by a process such as distillation.
The discovery of a roll of sheet zinc at Agora in Athens datable to 2nd-3rd century BCE is an interesting example of pure zinc. The Greeks were not producing such zinc at that time and possibly they obtained it from India. The Indians had certainly mastered the technique of pure zinc and high zinc brass earlier than their counterparts. In Asia Minor the source of brass was at Gordion in Turkey, which is referred to by the Greek writers Theopompus and Strabo as oreichalkos. Perhaps the Greeks, the Etruscans, the Romans, the Egyptians all might have learnt zinc and brass technique around the early centuries of the Christian era from India.
Though few brass objects have been found even in a Neolithic context in China it does not seem to have become common before the 16th century. Zinc smelting began in China in Jiajing period (1552 - 1566 AD) of the Ming dynasty in 16th Century AD, the evidence of which comes from the excavations at Gui-Zhou. It was exported to Europe in the end of the 17th Cent AD under the name totamu or tutenag. Tutenag possibly has its origin in the word Tutthanaga a name of zinc in South Indian languages. A seventeenth century Chinese author has written that Tutenag is a word from some foreign language. Thus there is textual and etymological evidence of transmission of ideas regarding zinc between the two countries. These facts together indicate that zinc was smelted about three centuries earlier in India (in 13 Century AD) than in China and these ideas were transmitted to China in the 16th century AD.
Taxila, located about 20 miles north of Rawalpindi in Pakistan, has yielded few brass objects such as two bangles, one vase and a pot datable to 3rd century BCE to 1st century AD. Some of them contain very high quantity of zinc i.e., 34.34%.
Among the old workings for zinc, the Zawar complex of Rajasthan in Western India is the most famous. Impressively abundant traces of old workings extend all over the 25 km mining belt and go down to a depth of 90 m below surface. It is claimed that the Zawar miners went up to depths exceeding 150m. The miners perhaps used wooden ladders, scaffolds and launders to drain water in the mines. The wooden samples of two such mines each at Zawar and at Mochina have been dated by 14C. These dates certainly suggest that in the second half of first millennium BCE extensive mining and smelting of lead-zinc ores were done in western India and perhaps the metal was supplied for various regions for coins and other objects. The earliest dates we have for zinc distillation are from a white heap, which is of the 12th century AD.
Despite the very early occurrences of accidentally produced brass in India, China and West Asia, deliberate pure zinc production was very late. The Zawar distillation industry was a unique phenomenon of Rajasthan, in India, which has stolen a march globally in the earliest production of zinc. The innovation of distillation technique of zinc in India is a glorious chapter in the global History of Science and Technology. The distillation technique and industrial production of zinc goes back to the 12th Century AD and possibly reached China from India in the 16th Century. In fact this is an important contribution of India to the world of science.
Zawar mines in Rajasthan show a continuous development of zinc smelting technology from mid-1st first millennium BCE and finally evolved into the sophisticated distillation process in the twelfth century AD. I propose to study this story of gradual evolution of zinc technology in India. And also how it spread all over the world.
In fact a large body of ancient Indian literature e.g. Mahabharata and Ramayana, Grihyasutra, Arthasastra, Ras-Ratnakara, Rasaratnasamucchaya refer to zinc and brass i.e. termed as arakutah, riti or pitala, jasada etc. This literature also reveals the method of production of zinc.
The innovation of distillation technique and industrial production of zinc in India is a glorious chapter in the global History of Science and Technology. Though there is considerable amount of literature available on archaeometallurgy, particularly on copper and iron technologies, there is very little literature on zinc, barring few papers by Craddock and his collaborators on zinc and brass. It was a momentous invention and a remarkable contribution of India in the global history of science and technology. A book on the metallurgy of zinc, brass and zinc distillation in India would, therefore, fill a lacuna in the history of science.