Glass Technology: processes and applications Harvard Graduate School of Design
Design concerns for base material of glass: transparency reflectivity color texture strength Design concerns for assembly: structural system thermal performance acoustical seal
Base material specified by fabrication process: Float glass: most common, relies on continuous production cycle Rolled glass: used primarily for specialty glass such as wired safety glass** Cast glass: for special forms, textures; glass block **Wired glass is required by fire code in critical locations to prevent catastrophic breakage during high heat conditions -- the integral wire restrains glass shards from flying out. Wired glass may soon be replaced in general usage as borosilicate safety glass becomes more affordable to produce.
Base material specified by color: Green glass: ordinary float glass has slight green tint Museum grade or "water-white" glass: green tint is eliminated by removing iron oxide from the glass chemical mix Body-tinted glass: integrally colored glass; rarely used in construction today due to improvements in surface tinting technology
Secondary processes: Tempering: after formation glass is reheated and quickly cooled to reduce normal surface tension; result is a glass 5x stronger than ordinary float glass; breakage, when it occurs, results in less dangerous, rounded shards Curving: modifying formed glass through reheating Laminating: transparent acrylic polymer used to fill cavity between two panes of glass; polymer adds strength and has adhesive function in failure (prevents glass shards from scattering)
Tertiary processes: Sandblasting: produces an irregular surface for a “frosted” or diffuse effect, transparency controllable by degrees; should be sealed afterwards in areas where people are likely to touch the glass. Etching: creates similar diffusing effect on surface using hydrofluoric acid to scar the surface of glass; self-sealing. Sputtering: microscopic spray coatings of various metals to vary the degree of light and heat transmission across the EM spectrum; mirror glass and “low-e(missivity)” glass are typical products; sputtering technology is also used for coloring and holographic effects. Fritting: a silk-screen printing of ceramic material is baked on to the glass surface; nearly infinite variability of patterns, transparency.