GLASS

Glass as a building material can be used to "contain" a space, as well as be transparent.  Glass can be a skin and also be used as a type of decoration.  What is on the other side of the glass can complement the exterior.

Here are two different examples of glass as a building material.  The exterior door is glass with BRASS fixtures.  Inside the lobby thick glass block is used as a defining wall for the Optomotrist.