Cast iron
Cast iron is made from pig iron, which is the product of smelting iron ore in a blast furnace. Cast iron can be made directly from the molten pig iron or by re-melting pig iron, often along with substantial quantities of iron, steel, limestone, carbon (coke) and taking various steps to remove undesirable contaminants. Phosphorus and sulfur may be burnt out of the molten iron, but this also burns out the carbon, which must be replaced. Depending on the application, carbon and silicon content are adjusted to the desired levels, which may be anywhere from 2–3.5% and 1–3%, respectively. If desired, other elements are then added to the melt before the final form is produced by casting.
SoHo, Manhattan
SoHo boasts the greatest collection of cast-iron architecture in the world. Approximately 250 cast-iron buildings stand in New York City, and the majority are in SoHo. Cast iron was initially used as a decorative front over a pre-existing building. With the addition of modern, decorative facades, older industrial buildings were able to attract new commercial clients. Most of these facades were constructed during the period from 1840 to 1880. In addition to revitalizing older structures, buildings in SoHo were later designed to feature the cast iron.