From the 17th century, sadirons or sad irons (from an old word meaning solid) began to be used. Made from thick slabs of cast iron, delta-shaped and with a handle, and 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. The method of heating it is as follows: - A piece of charcoal is placed on an iron spoon and ignited; when properly burning, it is placed in the hollow of the iron and surrounded by more charcoal. The lid is then fitted on the iron, which in a few minutes becomes sufficiently hot, and is then ready for use.