Decimus Burton's Palm House at Kew Gardens [Click on thumbnail for larger image.]More than a decade before the construction of the The Crystal Palace and Waterhouse's Natural History Museum at Oxford, writers on architecture like J. C. Loudon predicted new kinds of building based upon the use of iron. In 1837, the year Victoria come to the throne, "Loudon had forecast that the coming age of iron would mean an end to all established architectural systems: 'all habitual notions of ... proportion must, of course, be discarded.' Instead of adapting "the new material to their designs," architects would have to "adapt their designs to the new materials" [Crook, 105].
Nonetheless, despite the presence of some who thus looked forward to an Age of Iron, neither Paxton's Crystal Palace nor Waterhouse's Oxford Museum immediately ushered in the modernist archictecture and architectural theory they seem to portend. They did not do so for several important reasons, the first of which derives from the fact that, as Hitchcok and Crook point out, the criteria according to which such buildings might be understood and judged "still awaited formulation." Second, architects separated engineering and architecture, the latter being beneath them, and the Crystal Palace was categorized as a marvel of engineering — and hence irrelevant to the architect, who worked in stone. Third, innovative and intellectual theorists like Pugin and Ruskin did not like iron.
Not all reasons for the failure of iron to become a dominant architectural material involved matters of aesthetic belief or prejudice, for it proved itself neither as practical nor as safe as had been expected:
After 1855 and still more after 1870, building regulations in London actively discouraged the use of exposed-iron construction. Fire hazards, and the dangers of oxidisation and fragmentation, inhibited easy acceptance of the new material. By the 1870s not only had the search for an iron architecture been abandoned, a series of spectacular failures -- at the Surrey Music Hall, for example - had gone some way towards discrediting iron construction altogether. Steel was by then the material of the future. G. E. Street dismissed the search for a new, metallic architecture as "a wild goose chase." 
J. Mordaunt Crook. The Dilemma of Style: Architectural Ideas from the Picturesque to the Post-Modern. Chicago: University of Chicago Press, 1987.
Last modified 8 June 2007