New York has an enormous amount of architectural terra cotta on building facades, mostly installed between 1900 and 1930, although use started earlier and ended later. To really get a handle on the phenomenon, you have to look at it more as a moment in the history of building technology than the history of architecture. The building above, the Church of the Sacred Heart of Jesus, on 51st Street in Hell’s Kitchen, provides a good starting point. The picture shows a small portion of the front facade, with a side door, and two rowhouses and a tenement beyond.
Construction started in 1884 and the church opened in 1885. Construction supposedly finished in 1901, but when small churches from poor parishes took a long time to build, it usually means that ornate interiors were incomplete rather than the main body of the building. I’d guess the the masonry of the front facade was put up in 1884, not 1900. In any case, look at that terra cotta over the stone arch of the door:
It may not be to everyone’s taste – too busy, perhaps – but that is remarkable detail.[efn_note]We’ll all pretend we don’t see the plywood holding up the air conditioner.[/efn_note] Simply put, the red terra cotta ornament above the arch was much, much cheaper to create than the white limestone ornament of the arch. Putting aside the difference in difficulty in working with clay rather than stone, the terra cotta was a reproducible panel that could be made again and again using the same form, while each piece of stone had to be carved by hand.
Ease of construction and low cost are both important reasons why a new construction technology might drive out an older one. They are also linked: something that’s easier to build is usually cheaper. Brownstone was popular in New York in part because, being so soft, it was easier and cheaper to carve than limestone. Architectural terra cotta, once people got the hang of it, was easier and cheaper still. In addition, it could hold much finer detail than brownstone: there’s no way that the fine lines of that basket-weave pattern could have been made in brownstone. In the 1880s, the use of architectural terra cotta in the US was just becoming popular, and was often confined, as here, to ornament in the field of the wall rather than projecting cornices. As terra cotta’s use grew, it drive out carved brownstone ornament and then carved limestone and granite.