Glass used in structures.
Glass was first used for windows in Roman imperial times. Lack of transparency and the difficulty encountered in making any but small panes eventually led to the introduction of stained-glass windows in the 12th century. Clear, colorless glass proved difficult to achieve until the Venetian manufacture of cristallo (see Venetian glass ). Large sheets of glass first became practicable when the French introduced plate glass in the 17th century. Mechanization of glass forming did not occur until the late 19th century. The float-glass method currently in use, which eliminated the need for grinding and polishing, was introduced in the 1950s. Special glass products today include insulated (multipane) assemblies, laminated security glass (wired glass), and glass blocks and bricks (see masonry ).