By the 19th century two main types of iron had been developed - the flat iron and the box iron. Both irons were made out of iron, but the flat iron was solid, whilst the box iron was hollow on the inside. The flat iron was placed on the kitchen range to heat it up. But the box iron was heated by a piece of hot iron, known as a slug, which was also heated on the kitchen range and then placed inside the hollow. Two slugs were used during ironing so that one could always be heating up at the fire whilst the other was being used inside the iron.

The iron shown here has a wooden handle and a sliding door at the back, also with a wooden handle. The hot slug was put into the iron through this door although some box irons have a top that can be lifted off instead.

A variation on the box iron with a slug is the charcoal iron. With this, hot charcoal was put inside the hollow body of the iron. The advantage of using a hot slug, rather than charcoal, was that there were no fumes to escape and no sparks or smudges on the ironing.