Conservatories and exhibition buildings (ferro-vitreous art)
Iron frameworks were ideal for the structural support of conservatories and exhibition buildings and some of the most spectacular iron-frame buildings of the nineteenth century were of this type.
Horticulturists discovered that iron could be a suitable material for the slender glazing bars of their conservatories and planthouses. A theory of optics which held that the sun should pass through glass at right angles, led J. C. Loudon and others to promote the development of curvilinear iron and glass garden buildings. Loudon devised a wrought iron glazing bar for such purposes in 1816, which was put into production by an ironwork contractor: a palm house built on his system survives, recently restored, at Bicton in Devon. Glasshouses descended in type from Loudon's were widely used by the mid-19th century in botanic gardens, for instance the Palm House at Belfast 1839-1840 and the Kibble Palace at Glasgow 1873.
The Palm House at the Royal Botanical Garden, at Kew in London,was perhaps the most spectacular of the nineteenth century glasshouses.
Almost totally curved throughout, in both its wings and central lantern section, the Palm House at Kew is a convincing demonstration of the beauty inherent in iron construction. This is due partly to its size - 362ft (110 metres) long, 62ft (19 metres) high in the centre - and also to the decision of the ironwork contractor Richard Turner to substitute wrought iron for cast iron in the frame, thereby substantially reducing its weight and allowing more light to flow in and through the building. The ribs were based in the rolled wrought iron deck beams used in shipbuilding, supplied in 12ft. (3.7 metre) lengths, butt-welded and curved at Turner's works before being sent to Kew. The purlins were also of wrought iron, using a tensioned rod running through a pipe between the ribs. Turner went on to build railway train shed roofs on the same principles, notably the 153ft. 6in. (47 metre) span shed at Liverpool Lime Street 1849-1850.
The largest glasshouse of the nineteenth century was the Crystal Palace, constructed to house the Great Exhibition in London of 1852.
It is usual to assume that there was a direct line of development from glasshouses such as Turner's at Kew to the exhibition buildings of the 1850s and 1860s, especially the Crystal Palace. Superficially that was so, for they all used iron and glass to an extent that could not have been contemplated a few years earlier, but to stress the horticultural ancestry of the Hyde Park exhibition building and its successors is to misunderstand their real significance. The temptation to make that link stems from the heroic role normally assigned to Sir Joseph Paxton in descriptions of the Crystal Palace: the head gardener whose constructional genius saved the day. Paxton had been responsible for a series of glasshouses at Chatsworth, principally the Great Conservatory 1836-40, from which he took some of the ideas for the exhibition building. Ridge and furrow roofing, a concept first promoted by Loudon and developed by Paxton, was adopted as the key modular component, and the use of steam-driven machinery to produce timber sections was based on Chatsworth experience. But for the execution of his design, including the structural analysis and the completion of working drawings, Paxton relied on the ironwork contractors Fox Henderson and Co. They were, as one contemporary put it, "the masters of the situation". The experience that Fox Henderson brought to the Hyde Park project was a sign of the maturity that iron construction had reached by 1850. For while Paxton contributed his knowledge of timber construction, they were equipped to design, fabricate and erect the iron components that constituted the structural frame: cast and wrought iron trusses secured to the cast iron columns by wrought iron and wooden keys. Previously their major works had been as railway contractors and suppliers of bridges, dockyard roofs and prefabricated buildings: they went on to complete the train sheds at Paddington 1851-4 and Birmingham New Street 1854 (demolished). It is in the context of those and similar projects, rather than the glasshouse tradition, that the Crystal Palace takes its proper place.
Cast and wrought iron were superseded for structural frameworks by steel towards the end of the nineteenth century.
Industrial processes for the manufacture of steel were developed from the mid nineteenth century and by the end of the century this material had replaced iron as a structural framing material. Iron buildings were produced in the second half of the century but no significant innovations occurred and these made use of the techniques that had been developed earlier in the century.
