03-MAR-2016: Professor L A K Rao, Chairperson, Department of Geology, Aligarh Muslim University, recently presented an ancient retort dating back to 2, 500 years to the AMU Pro Vice Chancellor, Brigadier S Ahmad Ali (retd) to be kept in the University's Musa Dakri Museum. Prof Ali Athar, Chairman, Department of History was also present on the occasion.
With the recovery of the retort from the Zawar Mines in Udaipur district of Rajasthan, it is now believed that the area was the first to produce pure zinc, produced by distillation process on a commercial scale.
The finding of this retort is a testimony to the smelting process carried out by Indians for extracting zinc and lead on large scale in Zawar Village of Rajasthan.
Prof Rao said that a complete retort is 'cylindrical' and tapers at one end resembling a Brinjal (aubergine).
He added that retorts are either approximately 200mm long or 80 mm in diameter or 350 mm long and 150 mm in diameter.
He informed that cylindrical retorts are wider at the top and tapers at the lower end.
Prof Rao pointed out that the charge that was filled in these retorts was prepared by crushing and grinding the ore and mixing it with some organic material and cow dung. He further pointed out that the crushed ore was rolled into tiny balls and was left in the sun for drying and a thin wooden stick was placed in the narrow opening of retorts, which perhaps prevented falling of charge.
He further informed that the furnace in which these retorts were kept for smelting was divided into upper and lower chambers, separated by a thick perforated plate of clay.
"The retorts as many as 36 at a time were kept on the upper chamber in an inverted position, which would facilitate the escape of zinc vapour formed during heating," said Prof Rao adding that identification of different size of retorts is sure indication of different shape and size of furnaces at Zawar.
"After heating, zinc vapour was collected and condensed in the lower chamber in small earthen pots this was an ingenious method that was divided for downward distillation of zinc," said Prof Rao.
He concluded by saying that the analysis done on these retorts showed that, though the sphalerite and galena occur together in the ore but these are only in minor quantities (1.55% Pb) of lead in the retort's zinc as it was very mobile during melting, while lead was not.