Leather bookbindings in libraries have shown widely different rates of deterioration over similar time periods depending on a number of factors: 1) air pollution penetrating from the outside; 2) exposure to a location near ventilation or heating ducts, etc.; 3) the bookbinding process itself (how the leather was shaved or stretched) and on the kind of tannage that was employed, some tannages apparently being more resistant to pollution-induced deterioration than others. Concern over this situation led the British Library in 1976 to initiate and fund a new investigation to develop a stable tannage for bookbinding leather.