WINDOW TECHNOLOGIES: Surface Treatments

Detail view of frit glazing. Photo courtesy of Viracon; Photo: Wes Thompson

CASE STUDIES

The Debis Tower uses fritted louvers and skylights to diffuse the daylight entering the spaces.

The Hoffmann-La Roche Ltd. Office Building utilized acid-etched glass to diffuse light coming through transom windows that was too bright and directional.

Surface Treatments

Frit Glass
Silk-screening ceramic frit onto glass enables the designer to use color and patterns on architectural glazing. Combined with clear or tinted glass substrates, as well as high-performance coatings, fritted glazing can help reduce solar heat gain. An opaque frit pattern can help control glare but translucent frit patterns may provide diffuse light that increases glare.

Ceramic frit paint is comprised of minute glass particles, pigment, and a medium to mix the glass and pigment together. The paint is applied to one side of the glass—either heat-strengthened or fully tempered to prevent glass breakage due to thermal stresses under sunlit applications—and is fired in a tempering furnace to create a permanent coating. For an insulating glass unit, the silk screen pattern is ideally located within the sealed cavity for protection. Frit can also be applied to laminated glass units. A low-E coating can be placed on top of the frit. To reduce long-wave radiative heat gains, it is best to use the fritted layer on the interior surface of the exterior pane of an insulating glass unit.

White ceramic frit has been the predominant color, however, dark ceramic frits, such as neutral gray, black, and silver metallic are increasingly utilized. These colors also help reduce reflection and offer alternative design options without adversely affecting performance. Frit location—or multiple frit combinations—within a glazing assembly affect such factors as solar absorption, shading coefficient, and appearance.

The design flexibility—in terms of pattern and color—of fritted glass is appealing, but many manufacturers also offer standard patterns, such as dots, lines, and holes. Pattern coverage is specified, most often in the 40 to 60% range, with density naturally impacting glass performance characteristics and vision area. In practice, the SHGC of a frit coating is affected by its color and location in the window assembly.

Acid-Etched and Sandblasted Glass
Acid etching gives a matte finish to glass panes, with the degree of finish being determined by the length of time the acid is in contact with the surface. By masking, patterns and pictures can be etched into the glass to give the architect design flexibility. An intense etching process roughens the glass surface, which diminishes transparency. Light passing through the glass is scattered to obscure view and diffuse light. Glass can also be sandblasted to give a similar matte finish. It should be noted that diffusing glass can sometimes increase glare since surface brightness is increased.

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