With the heat and the weight of the ironing plate, the fibers are stretched and the fabric maintains its new shape when cool.
Some materials such as cotton require the use of water to loosen the intermolecular bonds. Many materials developed in the twentieth century are advertised as needing little or no ironing.
The electric iron was invented in 1882 by Henry W. Seeley, a New York inventor. Seeley patented his “electric flatiron” on June 6, 1882 (patent no. 259,054).
History
Metal pans filled with hot water were used for smoothing fabrics in China in the 1st century BC. From the 17th century, sadirons or sad irons began to be used. They were thick slabs of cast iron, delta-shaped and with a handle, heated in a fire. These were also called flat irons.
A later design consisted of an iron box which could be filled with hot coals, which had to be periodically aerated by attaching a bellows. In Kerala in India, burning coconut shells were used instead of charcoal, as they have a similar heating capacity.
This method is still in use as a backup device since power outages are frequent. Other box irons had heated metal inserts instead of hot coals.
Another solution was to employ a cluster of solid irons that were heated from the single source: as the iron currently in use cools down, it could be quickly replaced by another one that is hot.
In the late nineteenth and early twentieth centuries, there were many irons in use which were heated by a fuel such as kerosene, ethanol, whale oil, natural gas, carbide gas as with carbide lamps, or even gasoline.
Some houses were equipped with a system of pipes for distributing natural gas or carbide gas to different rooms in order to operate appliances such as irons, in addition to lights. Despite the risk of fire, liquid-fuel irons were sold in U.S. rural areas up through World War II.
In the industrialized world, these designs have been superseded by the electric iron, which uses resistive heating from an electric current. The hot plate, called the sole plate, is made of aluminium or stainless steel.
The heating element is controlled by a thermostat which switches the current on and off to maintain the selected temperature. The invention of the resistively heated electric iron is credited to Henry W. Seeley of New York in 1882.
In the same year an iron heated by a carbon arc was introduced in France, but was too dangerous to be successful. The early electric irons had no easy way to control their temperature, and the first thermostatically controlled electric iron appeared in the 1920s. Later, steam was used to iron clothing. Credit for the invention of the steam iron goes to Thomas Sears.