Spandrel glass speaks to what is spandrel glass and why use spandrel glass.
In fact frits are used to create special opaque glasses for covering spandrel areas, which are the bands of wall around the edges of floors, in glass curtain wall construction.
A uniform coating of frit is applied to what will be the interior surface of the glass. Some spandrel are made as similar as possible in exterior appearance to the glass that will be used for the windows on a specific project.
It is very difficult however even with the reflective coated glass, to make spandrels indistinguishable from the windows under all lighting conditions. Most spandrels are made to contrast with the windows of the building. Many suppliers can apply thermal insulation on the interior of the glass, complete with vapour retarder.
Spandrel is usually tempered or heat strengthened to resist the thermal stresses that can be caused by accumulation of solar heat behind the spandrel.
A spandrel, less often spandril or splaundrel, is the space between two arches or between an arch and a rectangular enclosure.
There are four or five accepted and cognate meanings of spandrel in architectural and art history, mostly relating to the space between a curved figure and a rectangular boundary - such as the space between the curve of an arch and a rectilinear bounding moulding, or the wallspace bounded by adjacent arches in an arcade and the stringcourse or moulding above them, or the space between the central medallion of a carpet and its rectangular corners, or the space between the circular face of a clock and the corners of the square revealed by its hood. Also included is the space under a flight of stairs, if it is not occupied by another flight of stairs. This is a common location to find storage space in residential structures.
In a building with more than one floor, the term spandrel is also used to indicate the space between the top of the window in one story and the sill of the window in the story above. The term is typically employed when there is a sculpted panel or other decorative element in this space, or when the space between the windows is filled with opaque or translucent glass, in this case called spandrel glass. In concrete or steel construction, an exterior beam extending from column to column usually carrying an exterior wall load is known as a spandrel beam.
The spandrels over doorways in Perpendicular work are generally richly decorated. The spandrel of doors is sometimes ornamented in the Decorated period, but seldom forms part of the composition of the doorway itself, being generally over the label.