STRUCTURAL GLASS FACADES - USC School of Architecture

Opacity is the opposite of transparency; no light passes through an opaque material. Glass
can be made opaque. Spandrel glass is opaque glass often used in curtain wall systems
over areas where clear glass, or vision glass as it is sometimes referred to, is undesirable,
as in the area between floors in a high-rise structure. Most commonly, a ceramic frit material
is applied to the glass and fused to the surface in a tempering oven. Is use in this manner
provides a continuous and consistent glass surface, which points out another noteworthy
attribute of glass; the surface quality is largely impermeable, durable and relatively easy to
maintain.
Between transparency and opacity lies the broad spectrum of translucency, the declared
domain of interest for Steven Holls, among others. Translucent materials allow light to pass
through, but diffuse the light by some means in the process. Translucent materials cannot be
seen through as transparent materials can, do to the diffusion of parallel light rays that
provide optical clarity. While no image is transmitted, the amount of diffused transmitted light
can be even more than that transmitted by a transparent material. Transparent and
translucent materials are rated by the percentage of light they allow to pass through, a
property called transmittance discussed in the following Chapter. Various techniques can
produce translucency in glass, among them; melt chemistry that produces clouded, milky
glass; sandblasting or coating of one or both surfaces of a glass pane; or the use of
translucent plastic laminates in the making of laminated glass products. The quality of light
and degree of translucency vary quite significantly among these different processes.
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