Bronze outdoor statues in London are almost invariably black, painted protectively in that colour, though originally just blackened with soot. A popular source of the bronze was captured cannon from defeated enemies, usually the French. Of course by Victorian times a range of metals became available - lead had often been used on smaller statues, and examples survive. But more importantly, with the Victorians introducing iron and then steel for large-scale building, their love of ornament brought cast sculpural ornamentation in these materials. Street lamps especially showed an astonishing variety of ornamentation - good examples in London are the dolphin lamps along the Victoria Embankment and the even more ornate ones at Trafalgar Square .
Railway stations are also particularly rich in foliated designs in iron.
Aluminium became low enough in price in the latter 19th Century to be usable for sculpture, and the most famous statue of this material is of course the Eros at Piccadilly Circus . Stone As noted, marble was always favoured for statues. But to be able to carve a stone, the neccessary requirements are that it be hard, and a freestone - that is to say, a stone that can be cut in any direction with equal facility and strength. While marble is ideal, and beautiful, both limestone and sandstone can be used, though their softer nature makes them subject to weathering. The cure for this is to protect the sculptural work in niches, or with eaves, as is done on church sculptural work.