Wrought means "worked" in medieval English, a time when
blacksmiths worked iron rods into intricate curving designs for
fences, furniture, gates and window boxes. Two kinds of wrought
iron are used. Charcoal iron was first forged in a charcoal fire
in the Iron Age and beaten into shape by hand. It was replaced
in the 18th century by smooth rolled bars and named "puddle
iron" during the Industrial Revolution, which created coal
furnaces.

Properties
Wrought iron is made of iron with less than 1 percent carbon and
a glass-like slag. It is the only ferrous metal that contains
siliceous slag. Wrought iron does not become molten in the
manufacturing process, so carbides and silicates are changed
into glass and remain in the matrix. These give wrought iron its
fibrous structure and anti-corrosive properties. While forged
wrought iron and mild steel, which replaced it in the 1800s,
appear identical, their working properties and resistance to
corrosion are very different. Wrought iron is softer and
workable at a higher heat than mild steel, which makes it more
malleable when beaten by a hammer. Before the 18th century,
wrought iron was forged into billets by water power or hand. The
surface of the bars was uneven and corners very sharp. Beginning
in the 19th century, cast iron was purified in a refinery and
renamed puddle iron, a form of wrought iron. The bars were
rolled smooth, which rounded the corners.
Uses
When wrought iron is heated, the slag melts and coats the
surface. This glassy layer gives it a shiny luster and retards
oxidation. Wrought iron can be heated to a higher temperature
than other metals, which makes it more malleable and easy to
form into elaborate designs. Wrought iron is durable; it has
been used in three 100-year-old ship beams and cramps on
500-year-old Tudor bridges still in excellent condition. Wrought
iron railings in England's Westminster Abbey are from the 13th
century.
Benefits
Wrought iron is not brittle and will bend, not break, allowing
delicate design work. Decorative wrought iron is full of
intricate forms and water traps that are notorious areas for
corrosion with other metals not protected by slag. Because of
its coating of glass slag, wrought iron is virtually maintenance
free and its low carbon content makes it relatively easy to
weld.
Modern Uses
Sharp points make ornamental wrought iron fences protective.
Iron and steel don't contain wrought iron's glass slag, so they
corrode rapidly. Although hand-made wrought iron is more
expensive to make, it lasts longer and requires less maintenance
than mild steel or cast iron. It is a good choice for an outside
decorative feature, like a gateway or door frame, and is a
favorite material for window boxes or balcony railings. Wrought
iron is preferable to modern metals to restore historic sections
of wrought iron work.
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