History of kansa
Bell metal is a hard bronze alloy used for making bells and related instruments, such as cymbals. It is a form of bronze with a higher tin content, usually in approximately a 4:1 ratio of copper to tin (typically, 78% copper, 22% tin by mass). The higher tin content increases the rigidity of the metal, and increases the resonance. It also has industrial uses, being specified for valve bodies, piston rings, bearings, and bushings.
Tin and copper are relatively soft metals that will deform on striking (though tin to a lesser extent than copper), but alloying creates a metal which is harder and less ductile and also one with more elasticity than either of the two metals. This metal combination produces a tough, long-wearing material that is resistant to oxidation and subject only to an initial surface weathering. Verdigris forms a protective patina on the surface of bells which coats it against further oxidation. Specifically, it is the combination of low internal damping and low internal sound velocity that makes bell metal specially suitable for resonant percussion instruments.
Most commonly, as per its colloquial name, bell metal has been and is used for the casting of high-quality bells. The metal used is a high-tin alloy of copper and tin with approximately a 4:1 ratio of copper to tin (78% copper, 22% tin). This is a much higher tin component than that used in statuary bronze.
A range of percentages of tin content can vary from 20 to 26%, depending on the founder who has arrived empirically at their own alloy ratio. It has been found that increasing the tin content increases the decay time of the bell strike, thus making the bell more sonorous. Taking into consideration overall properties, such as tensile strength, hardness, wear resistance, cast quality, sound, and cost, the optimum alloy can probably be obtained by having a type bronze composition as: ~20wt.%Sn, < 2wt.%Ni, < 1.5wt.%Pb, ~0.01wt.%P, < 1wt.%Sb, with balance of Cu. Bell metal in this range of ratios has been used for more than 3,000 years and is known for its resonance and "attractive sound." The crystal lattice formation of this alloy is able to absorb high-impact energies, such as from a bell clapper, without distortion, which is the case when the bell is struck. This results in a resonant sound and causes the bell to vibrate strongly in a complex nodal system.
In India, in the state of Assam, it is called kanh while in West Bengal and Odisha, kansa, it is called Kanchu in Kannada and is used for cooking and eating utensils. Sarthebari in Barpeta district of Assam holds a unique place in the production of kanh utensils. In Assam, utensils of kanh have many religious uses and the most unusual utensils, bata and banbati, are used to give offerings and puja or to show respect to honored guests and dignitaries. Belaguntha in Ganjam district, Kantilo in Nayagarh, and Balakati near Bhubaneswar are well known for this craft in Odisha. In the state of Kerala, urulis (odu vessels) bring back memories of chakka varatti (jackfruit halva). In summer when jackfruits are available aplenty, huge quantities of chakka varatti would be made in the backyard over a logfire and consumed in a trice, the richness of fruits, jaggery and ghee. Urulis are made from bell metal. Vengalai panai (also made from a kind of bell metal) is synonymous with a Tamil bride's first pongal when freshly harvested rice is offered to the sun god with turmeric and sugarcane.