When people think of a building’s glass, they are generally referring to its vision glass. That is the glass that occupants look through, hence the term “vision glass” to see the outside. Many buildings also have spandrel glass, which is opaque in nature and is meant to hide certain elements of the building that are between its floors such as structural columns, slab ends, duct work, wires, and so on.

The opacity of spandrel is usually achieved by adding an opacifier such as silicone-based paint or frit to the #2 surface of a single pane unit or #4 surface of a double pane unit. This glass is available in black, white, and everything in between. Muted colors like grey and navy are common, but spandrel glass is also available in vibrant colors such as yellow, orange, and red. While it contains factory flaws not acceptable with vision glass, it generally withstands the test of time unless the opacifier is on the #1 surface where it is subject to the elements.