History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c13.s2.t11.1

v1.c13.s2.t11.1

*Bronze (Cu-Sn)* : Besides the invention of Cu-As alloys, which were not very common in ancient India, bronze is the next copper base alloy acclaiming to have World wide revolution in the metals technology which gave a fresh self-defending power to human race and a boost to the cultural heritage. This alloy gained its popularity owing to its golden colour and added edge hardness in as cast condition (200-250 B.H.N.). Bronze is basically a cast alloy having 0 to 20% Sn in copper, to which Pb, Zn, and Ni are also added either as tramp element or purposely to change its properties. *Fig. 46* shows the binary phase diagram of Cu-Sn alloy which indicates a maximum solid solubility of Sn as 15% at 798°C. On solidification the solubility decreases precipitating out Cu- Sn compound which imparts hardness to the alloy. The chemical analysis of the ancient bronze objects have shown a variety of compositions all falling within the above range and having a cast structure. This reveals that manufacture of designed castings and their molding technology was already fully developed in the bronze age or even earlier.