India Was the First to Smelt Zinc by Distillation Process
By D.P. Agrawal & Lalit Tiwari
Zinc is a very interesting metal and was responsible for the innovation of
utensils of mock silver and coins of mock gold. Because of the low boiling
point (907°C) zinc is difficult to smelt. Brass (an alloy
of copper and zinc) however is known from even 3rd Millennium BC in China,
but brass can be produced from naturally occurring minerals containing zinc
and copper. Pure zinc could be produced only after the mastery of distillation
techniques, which have been described in our ancient chemical treatises. The
mines of Rajasthan have given definite evidence of zinc production going back
to 6th Century BC. Distillation process however was being used only from the
12th century AD, thus India is the first to produce zinc by distillation processes.
We are sure that the following story of early zinc production
and lead about the ancient Indian chemists and metallurgists will be of interest
to the students of history of science and technology.
Zinc is silvery white in colour, hard and brittle owing to its closely packed
hexagonal crystal structure. In the 17th and 18th century Germans called this
metal 'Caunterfeitum' or mock-silver because of its silvery white lusture.
Its boiling point is 907°C. The main minerals of zinc in nature are calamine
and sphalerite and mostly these occur in combination with the minerals of
copper, lead, silver and iron. There is confusion about early occurrence of
zinc and its extraction by the distillation process. The regular zinc production
by distillation started in India around 12th century AD and in China it is
not earlier then 16th century AD. As early as the 12th century AD, India produced
the metallic zinc by the sophisticated distillation process at Zawar in Rajasthan.
This technology of zinc manufacture is also described in several Indian alchemical
works of the mediaeval period including the 13th century Rasa Ratna Samuccaya.
The word used in this document to describe the distillation process involved
is tirakpatnayantra, which translated literally, means "distillation
by descending". Various zinc-smelting processes were also described in
the Sanskrit works of medicinal chemistry and alchemy, viz., Rasarnavam
Rastantram (500-100 BC), Rasratnakar (2nd century AD) and Rasprakash
Sudhakar (12th century AD). In China zinc was first reported in the 16th
century by the excavation in Gui-Zhan region of Yun-han, but the new research
by the Chinese scholars gives a clear indication that zinc smelting began
in China in the Jiajung period (1552-1566 AD) of the Ming dynasty. In 17th
century China exported zinc to Europe under the name of totamu or tutenag.
Tutenag possibly has its origin in the word Tutthanagaa maening
zinc in South Indian languages.
Vijaya Deshpande (1996:276-279) claims that zinc extraction in India had
definitely started by the 13th century AD at Zawar. The earliest literary
evidence for the production of metallic zinc on a regular basis comes from
India (Craddock 1987/88). There are references to burning a metal, rasa,
to produce an eye salve, which should refer to zinc placing its use in the
last centuries of the first millennium BC. The Rasaratnakara, which
was probably compiled in its present form in the seventh or eighth century
AD, is ascribed to Nagarjuna, the great Indian scientist who lived in the
14th century AD. It describes both the production of brass by the familiar
cementation process and of metallic zinc.
Zinc mine at Zawar
Willie (1989) has described that the ancient mines at Zawar
in Rajasthan are both open cast and underground. He has concluded that the
host rock at Zawar is metamorphosed, sheathed hard and compact dolomite, except
within the weathered zone. The abundance of charcoal waste and ash found on
the floor of the old mine has indicated mining by fire setting method, which
must have created acute ventilation problem inside the mine. The inner side
of the mine was worked very methodically; the floor was kept clean and well
lit by oil lamps placed at suitable distances. Clean drinking water was also
put in large earthen jars. Transport of the ore, waste, timber and water must
have been a major task and for this, good pathways were made with wood and
stone. On the outer slopes of the hills ample evidence has been found about
the techniques used for breaking and beneficiating the ore. The ore mineral
was hand picked and broken, when necessary using stone hammers and slightly
hollowed work stones. In the recent excavation of Zawar region several uncovered
banks of furnaces were found. These furnaces were outlined in the Rasa
Ratna Samuccaya and these are just like an industrial version, with banks of between
three and seven furnaces and each furnace held 36 retorts (Craddock 1987:183-191).
Smelting process of zinc
There are few metals, which are produced by the reduction
distillation technique, and zinc is one of them. Craddock et al (1985) have
mentioned that distillation technology and apparatus were used in ancient
times in India for the process of distillation of water, wine, mercury and
zinc. The process used for the distillation of zinc in Zawar mines is unique
because it is designed on the basis of downward distillation. After the sizing
and beneficiation, the ore was mixed with charcoal dust and fired in to a
heap to convert it in to oxide. This roasted ore was again mixed with more
charcoal powder, salt and borax as flux and thoroughly mixed with cow dung
and water, then made in to balls of 5 to 10mm diameter by hand rolling. These
pellets were dried in sun and then filled into the brinjal shaped retorts.
The retorts are of two sizes with capacity of 750 and 2000cc. In the excavation
at Zawar region these retorts have been found. Each distillation unit had
two parts, a lower condensing chamber and upper main furnace chamber. The
lower chamber was square in plan and separated by perforated bricks from the
upper chamber, which was in the form of a truncated pyramid. The internal
dimensions of the furnaces (taken from furnaces 3 and 4) at the base were
660mm ´ 690mm, being slightly wider across the side with the entrance to the
lower chamber. The division between lower chamber and the furnace proper was
made by four of the perforated bricks (55mm thick), fitting closely together
and resting (but not mortared) on a projecting brick ledge at the side with
a single clay peg providing support in the centre. The use of a peg was necessary
to reduce absorption to a minimum as the lower chamber, which contained the
collecting vessels, was entered through just one small opening. Each of the
perforated bricks had 9 large (35 mm diameter) holes to accommodate the condenser
necks and 26 smaller holes (plus 9 shared with neighbouring bricks) for the
passage of air into the furnace and for ash to drop through (Craddock et al,
In this apparatus, at high temperature, solid charge was
held in to upper inverted pot by sealing its mouth with clay and fixing a
reed stick in the centre for the escape of gases etc. Another matching earthen
pot was kept into a trough full of water. During the processing the upper
inverted pot was heated by building a fire on a platform around it. On reaching
the cherry red temperature (600ºC) the reed was charred and brunt off
and the reduced metal vapours were forced downward into the condenser where
it got deposited into liquid or solid metal.
The distillation technique of zinc and heating from outside
was traditionally similar in both India and China but condensation method
of zinc vapour was different. A rough and conservative conclusion suggests
that perhaps 2,50,000 tonnes of zinc concentrates were extracted from some
2.5 million tonnes of ore in the total mined area before modern mining commenced.
The Zawar industry is the most unusual phenomena of a fully-fledged technology
with neither antecedents nor successors and apparently no contemporaries either,
for even within India it seems unique.
Agrawal, D.P. 2000. Ancient Metal Technology and Archaeology
of South Asia. New Delhi: Aryan Books International.
Craddock, P.T. 1987. The early history of zinc. Endeavour
Craddock, P.T. 1987-88. The early history of zinc and brass.
Wiener Berichte uber Naturwissenschaft in der Kunst 4/5: 225-45.
Craddock, P.T., I.C.Freestone, L.K.Gurjar, K.T.M. Hegde
and V.H. Sonawane. 1985. Early zinc production in India. Mining Magazine.
Craddock, P.T. and W.Zhou 1999. Traditional zinc production
in modern China: survival and evolution. BUMA conference Proceedings
Despande, Vijaya 1996. A note on ancient
zinc-smelting in India and China. Indian Journal of History of Science
Hegde, K.T.M., P.T.Craddock and V.H.Sonawane. 1984. Report
on the Excavation of Ancient Zinc Smelting Furnace at Zawar, Rajasthan.
Prakash Bhanu.1997. Metal and metallurgy. In History
of Technology in India (Ed.) A.K.Bag. New Delhi:
Indian National Science Academy. Pp.136-143.
Sing R.D. 1997. Mining. In History of Technology in India
(Ed.) A.K.Bag. New Delhi: Indian National Science Academy. Pp. 62-68.
Willies L.1984. Ancient lead and zinc mining in Rajasthan,
India. World Archaeology 16(2): 222-33.
Willies L.1987. Ancient zinc-lead and silver mining in Rajasthan,
India. BULP Interim Report