Metal windows in historic structures are often composed of one of three materials: wrought iron, cast iron, or mild steel. Wrought iron components have a deeper profile and a more repetitious look. From the First World War through the 1970s, mild steel windows were widely made. They are now rare except in modified commercial buildings. Cast iron components are heavier than steel windows and have a more elegant look. They are also less likely to distort from heat. The first cast-iron windows were manufactured in America around 1855. By 1870, most American cities had adopted this new technology as it was believed to be more durable than glass. In Europe, windows started being made out of cast iron around 1890. It was used by itself or combined with other materials such as glass, wood, or steel. Today, it is common to find single-glazed windows made out of cast iron on farms all over Europe. The modern metal window has its origins in the casement window, which consists of two pieces of glass set in a frame attached to a wall via wooden brackets called jamb rings. The frame may be made of wood or metal. In fact, most metal windows used today are based on some variation of the casement window design. Casement windows can be opened and closed using a knob or lever on the outside of the frame. This allows for ventilation without completely exposing anyone inside the home to the weather.