The metal that brings shelter and good health to India's poorest. Presenter Laurence Knight travels to a bustling Delhi where Rahul Sharma of the International Zinc Association explains how this self-sacrificing chemical element fights off the ravages of the city smog, while Dr HP Sachdev runs us through its medical benefits.

In Rajasthan Sunil Duggal, chief executive of Hindustan Zinc Ltd, explains how mining operations such as at the gigantic Rampura Agucha will help feed India's coming construction boom. Meanwhile, back in London Justin Rowlatt blows his trumpet.

(Picture: Slum rooftops in Mumbai; Credit: Daniel Berehulak/Getty Images)