When float glass comes off the manufacturing line it is a flat sheet. However, glass can be made to bend when the need — or design – calls for it. Bent glass is also called curved glass and can be found in vehicles (many windshields and some backlights are curved on the edges) as well as in architectural designs, from glass domes and hand rails to revolving doors and display cases. Due to the brittleness of glass, bending must happen while the glass is still warm enough to be manipulated but not so hot that it is molten. To bend glass, manufacturers place a piece of glass over a piece of metal made to simulate the curve needed for the glass. Both the metal and glass are placed into an oven and heated until the glass begins to soften, at which point both the glass and the metal form are removed from the heat. If left alone, gravity will pull the softened glass down and onto the shape of the intended curve, or an outside force can apply pressure to hasten the bending process.