Window Tinting Definitions

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Colored translucent glass, often called art glass, opalescent glass, cathedral glass or stained glass, is also produced by the rolling process, but generally in small, batch type operations. There are usually variegated colors within each sheet produced, and no two sheets will match for hue. Thickness will vary within a sheet, as well as from sheet to sheet. The maximum thickness produced is usually 1/8″. When used as a glazing material, art glass should be glazed in the same manner as tinted / heat absorbing glass. Art glass cannot be tempered.

Figured / patterned glass is produced domestically by the continuous pour process in thicknesses of 1/8″ to 7/32″. A pattern etched on one or both of the rollers is reproduced on the glass. Colors are available but are extremely limited. This type of glass is frequently called “obscure” or “decorative” glass. The pattern diffuses the detail of objects viewed through the glass; it does not obscure them. The degree of diffusion achieved is a function of the pattern and whether the pattern is on one or both sides. Some patterns cannot be tempered for safety glazing use because of their depth.

The float glass process accounts for over 90% of the flat glass presently produced in the United States. In this process, molten glass is poured continuously from a furnace onto a large bed of molten tin. The molten glass literally floats on the tin, spreading and seeking a controlled level in the same manner as water poured onto a smooth, flat surface. In the controlled level seeking process, the molten glass is allowed to spread to a width of 90″ to 140″, depending upon the furnace size and glass thickness being produced. The glass slowly solidifies as it travels over the molten tin. It is then cooled under controlled conditions. Afterward, it emerges as a continuous ribbon of glass at essentially room temperature. The product is now flat, fire-finished, and with virtually parallel surfaces.

Laminated glass consists of two or more plies of glass interleaved with clear or tinted polyvinyl butyl (PF). The application of heat and pressure bonds the glass and plastic interlayer into one unit. When laminated glass is fractured, the particles of glass tend to adhere to the plastic, affording protection against flying or falling particles. Some combinations of glass and plastic thicknesses do qualify as safety glazing materials under the criteria of ANSI Z97.1-1984 and CPSC 16 CFR 1201.

Low-emissivity coatings (Low-E) reflect the part of the heat spectrum above 3000 milli-microns wavelength that is called “sensible heat”. The heat from hot water or steam radiators and the heat from hot air ducts from a furnace are typical examples of this kind of heat. These coatings have high visible light transmission. In fact, they are nearly invisible on the glass. The visible light transmission is typically about 20 percentage points below that of an equivalent uncoated glass. The major attribute of Low-E insulating units is their sensible heat reflecting characteristics which is apparent from their low U-values. Low-E coatings are applied to glass by vacuum processes and by pyrolytic processes.

Most mirrors are manufactured by the wet chemical deposition method, although a few are made by vacuum deposition for specialized use. Safety mirrors are available to meet various laws and building codes. A mirror made from tempered glass will have the inherent distortion from the tempering process and cannot have the same quality in reflection as laminated ones made from mirror quality annealed float glass. Transparent, or two-way mirrors, are designed to allow vision through from one direction while presenting a mirror appearance from the opposite side. Their major application is to permit undetected observation for study or surveillance in places such as prisons, gambling casinos, and psychiatric treatment centers. A difference in lighting level is necessary. In the room to be studied the lighting level should be at least five times greater than the lighting level in the observation room; ten times greater is even more effective. Two way mirrors are not intended for use in exterior walls.

Spandrel glass panels are heat strengthened or tempered glasses with a ceramic frit color permanently fused to one of the surfaces. Glass in spandrel areas is not subject to corrosion, as are some other spandrel materials. Pleasing aesthetics and economies can be obtained using a single framing system for an entire wall. Glass spandrel panels can also save energy when insulation is placed behind them.

Tempered glass is fabricated by subjecting annealed glass to a special heat-treating process. The most commonly used process is to heat the glass uniformly to approximately 1150° F and then rapidly cool it by blowing air uniformly onto both surfaces simultaneously. The cooling process locks the outer surfaces of the glass in a state of high compression and the central portion, or core, in compensating tension. The color, clarity, chemical composition, and light transmission characteristics remain unchanged. Likewise, compression strength, hardness, specific gravity, expansion coefficient, softening point, thermal conductivity, thermal transmittance, and stiffness are unchanged. The only physical property that changes is tensile or bending strength. Under uniform loading, tempered glass is about four times stronger than annealed glass of the same size and thickness, and is thus more resistant to thermally induced stresses, cyclic wind loading and hail stone impacts. When broken, tempered glass breaks into a multitude of small fragments of more-or-less cubical shape. Therefore, it qualifies as a safety glazing material under the criteria of Federal Standard 16 CFR 1201 and the American National Standards Institute (ANSI) Z97.1-1984, when so labeled and certified. Spots or blotches may be visible on tempered glass, especially when viewed through polarizing lenses or in certain types of reflected light. The intensity will vary with lighting conditions and viewing angle. This is caused by the strain pattern induced during the cooling stage and is not inherently a cause for rejection.

Tinted or heat absorbing glass is made by adding various colorants to the normal, clear glass batch to create a desired color. The four colors available by the float process are bronze, gray, green, and blue. Visible light transmittance will vary from 14% to 83%, depending upon color and thickness. The color density is a function of thickness, and increases as the thickness increases; visible light transmittance will decrease as thickness increases. Tinting reduces the solar transmittance of glass, has little effect upon solar reflectance, and hence increases solar absorption (heat). This explains why heat strengthening or tempering is sometimes required for the thicker tinted glasses. Adding a metallic coating also has the same effect on thinner glasses.

Wired glass is produced on the same equipment as figured / patterned glass. A welded wire netting or parallel wires are introduced into the molten glass just before entering the rolls to embed the wire into the glass. Patterned wired glass has a pattern on one or both sides and is sometimes called “rough” wired glass. Polished wire glass is produced by grinding and polishing rolled wired glass blanks. Tinted / heat absorbing wired glass is available only as an import. The heat absorbing characteristic in conjunction with the normally poor cut edges and the wire netting can cause a high rate of breakage from thermal stress, especially in non-vertical applications. The major uses of wired glass are in institutional buildings and fire rated windows and doors. All wires must be completely embedded in the glass. Some misalignment of the wires may be noticeable, but this is not considered cause for rejection. Wired glass cannot be tempered.

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