Spandrel glass is a type of opacified glass that is used in a façade to conceal areas between floors of a building where structural, mechanical and electrical elements would otherwise be visible to those looking in. Spandrel glass is produced by applying an opacifying agent - which typically comes in the form of a ceramic frit or silicone-based paint material - to a glass substrate. Spandrel glass comes in a wide array of different standard and customizable colors allowing it to be used to aesthetically compliment adjacent glass or other building materials or finishes. Because spandrel glass tends to exhibit higher heat absorption characteristics, Hartung requires that all spandrel products be heat treated to address heightened thermal stress conditions that could adversely affect glass and window seal durability. Spandrel glass is not intended for use in applications that lack a uniform, opaque backdrop or in areas where the spandrel material will have direct outdoor exposure.