Biswas, Arun Kumar. 1994. Minerals and Metals in Ancient India. Vol. 1
Archaeological Evidence. New Delhi: D. K. Printworld (P) Ltd..
by DP Agarwal
A.K. Biswas has recently brought three
volumes on ancient metals. We propose to review them soon in detail. Here we are
only giving a brief summary of the
chapter on Zinc in the above-mentioned book by Biswas. Since zinc production is
a glorious chapter of Indian metallurgy, in which India led the world, it’s a
very useful reference work.
Biswas describes the earliest method of
making brass by the cementation process in which finely divided copper fragments
were intimately mixed with roasted zinc ore (oxide) and reducing agent such as
charcoal, and heated to 10000C in a sealed crucible. Zinc vapour
formed dissolved into the copper fragments yielding a poor quality brass, zinc
percentage of which could not be easily controlled.
Copper alloying with zinc (brass making)
is a delicate and well-controlled process. Reduction of zinc oxide around 10000C
is crucially important; as below 9500C no zinc is produced. If there
is a trace of oxygen then zinc vapour would be reoxidised and hence the
successful operations must have been done in closed crucibles. If the
temperature was higher than 10830C, copper melted and flowed down to
the bottom of the crucible forming a puddle there, exposing very small surface
area of the metal for alloy formation.
Brasses containing up to 36 per cent
zinc are known as a-
brasses, which undergo easy cold work (hammering in cold condition). Brasses
containing more than 46 per cent zinc are brittle. With zinc content between 36
to 46 per cent, we have a+b
brasses which are lighter, harder and more suitable for casting statuary.
Biswas quotes Werner and Haedecke who
demonstrated experimentally that brass produced by the cementation process could
not have more than 28 per cent zinc. The brass founders trying the cementation
process have verified this observation.
The materials must have been prepared by
mixing of the two metals, which could have been possible only after discovery of
zinc as a separate metal and its preparation by a process such as distillation.
The antiquity of brass artefacts can therefore be divided into two eras - one
preceding and the other following the discovery of zinc as a separate metal.
Biswas claims that the earliest
artefacts noted so far containing zinc are from India. Lothal (2200-1500 BC)
showed one highly oxidized antiquity (no. 4189), which assayed: 70.7 percent
copper, 6.04 zinc, 0.9 Fe, 6.04 acid-soluble component.
Similar materials might have been used
for making the brass-bronze items of Atranjikera during the Painted Grey Ware
era (1200-600 BC ?). One copper item contained 11.68 % Sn, 9.0 Pb and 6.28 Zn;
another item assayed 20.72 Sn and 16.20 Zn.
Biswas informs that Craddock has
surveyed the evidences of early brass artefacts in the West. The earliest
brass artefacts known come from the excavations at the Gordion Tomb in Phrygia,
dating from the eighth and seventh century BC onwards.
Biswas gives the composition of
a 4th Century BC brass sample which contained 34.34 % zinc,
4.25 Sn, 3.0 Pb, 1.77 Fe and 0.4 Nickel. This is a very strong evidence for the
availability of metallic zinc in the fourth century BC.
The earliest C- 14 dates in the Zawar
mines are 430+100 BC ( PRL-932) from the Zawar Mala Mine and 380+ 50 BC (BM
2381) from the Mochia mine. Similar dates from Rajpura-Dariba (e.g. 375 BC),
Rampura-Agucha (370 BC) etc. confirm the widespread underground mining of
lead-zinc ores in the southern Rajasthan during the fifth-fourth centuries BC
onwards. (For C-14 dates and other details of Zawar mines see also our essay,
“India Was the First to Smelt Zinc by Distillation Process,” on this
that the use of brass is attested for the circular punch- marked brass coins of
Dhanadeva and Aryavarma of Ayodhya (circa 1st century BC), as
also in Arthsastra. Both Kautilya and the earliest Indian brass of Taxila
belonged to fourth century BC, while the earliest C-14 dating of Zawar Mine is
gives the example from Rampura-Agucha where the zinc-lead-silver ore in the site
was selectively mined at least as early as 370 and 250 BC. An appreciable amount
of zinc must have been separated from the zinc-rich ore. One sample of slag
assayed as low 0.01 per cent zinc. Near the slag dump area several retort-like
pieces were reported.
A more popular
name for brass in the ancient India was riti or ritik, which also
meant calx of brass. The word was probably derived from harita or yellow
which had been a synonym for gold in the Vedic literature. The word was chosen
on account of the yellow colour of gold-like brass. The writings of Manu,
Yajnavalkya and Patanjali of the pre-Christian era sometimes refer to bronze (kamsya)
and brass (ritika) almost synonymously.