Glass manufacturers had spent centuries learning how to make flat glass. Now, they wanted to bend it into complex shapes—without marring its surface. Anything that touched the surface of the hot glass could leave a mark.
The first curved windows were made by slumping. A glass sheet was placed in a gravity mold that touched only its edges, then was heated from above until it sagged into shape. Slumping worked for windows with simple curves, but it was of no use for making the more complex shapes that car designers demanded.
Then, General Motors asked for the seemingly impossible: an exotically contoured window for its new 1984 Firebird. There was no way to make the complex curves without touching the glass. American glassmaker Libby-Owens-Ford had to take a bold step. It tried press-bending the precisely heated glass in an experimental full-contact mold made of a high-tech ceramic. The process worked. For the first time, glassmakers could totally control the shape of a window without marring its surface.