Blown sheet glass had been made from the 11th century forward, first in Germany, famously at Chartres (windows are of the early 13th century) and with Venice as the center of all glass by the 13th century. In the late 17th century in France an important innovation in 2D glass was the pouring of glass onto iron casting tables. Bernard Perrot (1619 – 1709) pioneered this method of casting and rolling glass which resulted in large and uniform sheets of glass, strong enough to be used in carriages and transparent enough for the greater production of mirrors (Versailles’ Hall of Mirrors dates from 1678-84). It is also in the 17th century that works of drawings and other art works began to be glazed.
By the 18th century, paintings showing cracked and broken glass panes covering works on paper, became popular subjects for trompe l’oeil artists.
Glass protects art works from dust and insects alighting, but exposes art works to destructive ultraviolet rays. Nowadays, plexiglass, the type developed specifically to block UV rays, is used for glazing. However, pastel drawings, are still framed with glass because the static charge of plastic can lift the pastel powder away from the paper. When glazed pastel drawings are transported, the glass must be carefully taped so that if the glass breaks it won’t gouge the artwork.
The best way of seeing a drawing is without glass or plexiglass. In the trompe l’oeil paintings above, the glass color was probably enhanced to help the visual deception, still, the difference between the glazed and unglazed sections is very telling. Even today’s near flawless glazing materials create a barrier to seeing and understanding.