Iron-frame architecture, which flourished primarily in England, France, and (later) the United States, occupies the transitional phase between traditional and modern architecture. Iron-frame buildings were erected mainly during the "age of iron and steam" (ca. 1750-1900). As noted earlier, this architecture included iron-frame masonry buildings, iron-and-glass buildings, and iron bridges.
Utilitarian structures (and utilitarian products in general) were important for demonstrating the aesthetic potential of plain, mass-produced objects. For instance, whereas iron supports in grand architecture were often hidden behind masonry (such that the buildings retained a traditional appearance), they were left exposed in structures where appearance was deemed unimportant (e.g. mills, factories) or where masonry was unnecessary (e.g. bridges, railway stations). Utilitarian buildings also often lacked traditional ornamentation, again due to lack of concern for appearance. As the nineteenth century drew on, many architects began to embrace these features (plain industrial materials and lack of ornamentation) as aesthetically desirable.F89,H1013