Modern architectural designs often require glazing materials that provide enhanced levels of security and safety performance properties. These properties include: resistance to ballistics, blast, hurricane/cyclic wind pressures and physical attack. Applications may also require desirable properties such as sound reduction, fade resistance, and solar & thermal control. Laminated glazing materials consist of multiple plies of glass, interlayers, resins and/or plastic glazing materials (such as polycarbonate sheet or acrylic), which are often complex in nature. They are designed to provide specified levels of performance.
Design professionals and building owners should be aware of the following considerations when selecting and specifying laminated glazing constructions:
Aesthetic Color
Commercial clear float glass is nearly colorless, however, a green or blue-green tint, which is faint in thin glass may become noticeable in glazing applications where the glass thickness exceeds 3/8” (10 mm). Laminated glazing materials, utilized for their impact resistance to ballistics, blast and physical attack and for additional applications such as zoo exhibits and large aquariums incorporate numerous plies of transparent glazing materials. In these applications, the thickness of the glass portion of the laminate often results in a more apparent degree of green. In some instances, the green tint is not as pronounced, as it can be disguised by the blue color of the water or the color of painted walls in an aquarium. The green tint also may not be as apparent in certain constructions such as glass-clad polycarbonate laminates that contain more polycarbonate than glass.
However, in certain applications, the green tint may be regarded as aesthetically displeasing to a designer and owner. For those projects that require the highest level of color clarity, low-iron clear float glass should be considered. Low-iron clear float glass may also assist the designer in providing a closer color match to a less thick glass that is in proximity to the laminated glazing.
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Many laminated glazing components are designed to block ultraviolet light (energy wavelengths from 280nm - 380nm); however, these components also block a portion of the visible light spectrum (wavelengths from 380nm – 420 nm) with a result that there may be a slight yellow appearance. This yellow appearance, not visible in single or thin multiple layers, may become noticeable when these materials are used in thicker or a greater number of multiple layers. This color should be considered in conjunction with color imparted by the glass itself.
There are also design considerations, which must be taken into account when a low e or reflective coating is used in the construction of a laminate. When the coating, applied to the glass substrate, is placed in contact with the PVB, the refractive index of the coating is changed and will result in a perceived color shift. This means that a coating in an IG unit may appear a different color than the same coating in a laminate.
Optical Distortion
Heat-Treated Glass
Images viewed in reflection from and by transmission through laminated glazing materials may be distorted. Both reflected and transmitted optical distortion may result from heat-treatment of glass, thickness variability of the materials used, mechanical stresses applied by the framing system and changes in exterior wind pressure and interior building pressure.
Laminated glazing materials may incorporate multiple plies of heat-treated (e.g. heat strenghtened, tempered) glass in order to achieve high levels of resistance to thermally and mechanically applied loads. Bow, warp and roll wave distortion are inherent characteristics of heat-treated glass. While fabricators take steps to minimize these conditions, they cannot be eliminated. All of these characteristics are accentuated by the use of reflective coatings and tinted glass substrates. Since transmitted distortion is dependent on overall thickness variability, it tends to be exaggerated by multiple plies of glass and other components. The thickness variations of the individual plies is additive. Laminated constructions incorporating annealed glass typically exhibit less reflective and transmitted optical distortion. Distortion in all glazing materials may occuras a result of glazing system, wind load pressures and overall bow and warp.
The visibility of reflective distortion is greatly affected by surrounding conditions and glazing orientation. If the reflected image is a uniform blue sky, the reflective image that appears in the laminated product may appear without distortion. If the same laminate is reflecting multiple gridlines from an adjacent building, the reflection may appear distorted. Roll wave distortion may be more visible by reflectance and transmittance when the direction of the wave pattern is glazed parallel to the jamb or vertical dimension of a window or door. In this application, images of lineal objects (such as building walls, utility and flag poles) and moving objects (such as cars and aircraft) become more visible as the viewing angle changes. In order to decrease the visibility of roll wave distortion in heat-treated laminates, fabricators commonly recommend and design professionals specify that the wave direction (wave’s peak) be glazed parallel to the sill of a window or door whenever possible. It is recommended that the manufacturer be notified in writing of these instructions prior to the onset of glass fabrication. Heat-treated glass fabrication equipment
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limitations may not allow roll wave orientation to the sill when the width dimension of a lite of glass exceeds the height dimension.
Multiple-Ply Laminates
Multiple ply glazing materials that include non–glass components such as interlayer films and/or plastics sheet products such as polycarbonate or acrylic sheet may also be a source of unwanted optical distortion. Special consideration should be given to these types of laminates.
Both glass (as previously described) and non-glass components may have thickness or flatness variability that creates lens effects, which may cause distortion of images when viewed through the glazing material. The magnitude and spacing of this variability are both important factors when trying to assess the suitability of a multiple-ply laminate for a given application as a precise alignment of the components containing this variability is not possible. Since this distortion is greatly affected by viewing angle, vertical lens lines are generally more objectionable
High performance plastic sheet used in multiple-ply laminates are most often either polycarbonate or acrylic sheet.
Acrylic sheet materials are produced by several processes, which exhibit varying degrees of distortion and thickness variations. Polycarbonate sheet is produced by an extrusion process, and therefore exhibits die lines (ripple direction) on both coated and uncoated polycarbonate, which may produce an objectionable distorted image. This distortion can be minimized by placing the ripple direction horizontal to the plane (when feasible) OR it is often preferable to orientate these die lines horizontally if possible. While plastic sheet manufacturers take steps to minimize these conditions, they cannot be eliminated.
Designers are recommended to further consider other conditions, such as: thermal expansion/contraction properties and changes in humidity, which may cause the plastic glazing material to bow, wan or warp; adequate space within frame systems to reduce perimeter issues due to edge pinch and, localized areas of distortion resulting from small particulate inclusions (fish-eyes) on coated plastic sheet materials. As more individual plastic layers are utilized in the laminate, distortion may become more pronounced.
Multiple-Ply Laminates incorporating both glass and polycarbonate components and their appropriate interlayer(s) are further described within ASTM C1349 Standard Specification for Architectural Flat Glass Clad Polycarbonate, and its Appendixes. Additional reference to the plastic sheet components and these types of laminates can also be found within the GANA Glazing Manual and the GANA Laminated Glazing Reference Manual. Refer to ASTM D 4802 Standard Specification for Poly (Methyl Methacrylate) Acrylic Plastic Sheet for the methods by which acrylic plastic sheet is produced and other specifications.
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Iridescence
When viewing laminated glazing constructions, under certain conditions, a pattern of iridescent spots or darkish shadows may become visible. This is commonly referred to as the strain pattern of the heat-treated glass and is related to the stresses introduced in the cooling process of the glass fabrication. While not normally visible, the strain pattern may become more evident by reflectance and in transmittance when viewing the glazing material at severe angles or under polarized light conditions. The potential of the iridescence becoming more pronounced is enhanced as the thickness of the laminated glazing material increases. The strain pattern is inherent in those heat-treated components and is not a result of discoloration or non-uniformity.
Product Awareness
As the design thickness of multiple plies of heat-treated glass and/or glass and polycarbonates increases to meet application requirements, the potential for distortion of images viewed through the glazing also increases. The bonding of multiple surfaces accentuates distortion as a result of the inherent variations in flatness of the component materials. Design professionals and building owners must be particularly aware of these characteristics in applications that involve viewing moving objects through the glass.
It is essential that design professionals consult with fabricators and suppliers in the early stages of design and engineering, given the sophisticated nature of laminated glazing materials required for optimum performance in safety, security, hazard resistant and sound reduction applications. Awareness of the laminated glazing product construction and inherent characteristics of the laminated glazing can dramatically affect the design application. Design professionals and building owners are strongly encouraged to utilize full-size mockups for evaluating the appearance of the glazing system under the specific project conditions, lighting conditions, and surrounding landscape. Utilization of a mockup is an inexpensive and reasonable process to ensure the product(s) and project design(s) meet a client’s expectations.
This bulletin was developed by the GANA Laminating Division – Optical Distortion Task Group and approved by the Laminating Division
– Technical Committee and GANA Board of Directors. This is the original version of the document as approved and published in October
2003. This edition of the bulletin provides the most recent update and published in July 2008.
Design professionals and building owners should be aware of the following considerations when selecting and specifying laminated glazing constructions:
Aesthetic Color
Commercial clear float glass is nearly colorless, however, a green or blue-green tint, which is faint in thin glass may become noticeable in glazing applications where the glass thickness exceeds 3/8” (10 mm). Laminated glazing materials, utilized for their impact resistance to ballistics, blast and physical attack and for additional applications such as zoo exhibits and large aquariums incorporate numerous plies of transparent glazing materials. In these applications, the thickness of the glass portion of the laminate often results in a more apparent degree of green. In some instances, the green tint is not as pronounced, as it can be disguised by the blue color of the water or the color of painted walls in an aquarium. The green tint also may not be as apparent in certain constructions such as glass-clad polycarbonate laminates that contain more polycarbonate than glass.
However, in certain applications, the green tint may be regarded as aesthetically displeasing to a designer and owner. For those projects that require the highest level of color clarity, low-iron clear float glass should be considered. Low-iron clear float glass may also assist the designer in providing a closer color match to a less thick glass that is in proximity to the laminated glazing.
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Many laminated glazing components are designed to block ultraviolet light (energy wavelengths from 280nm - 380nm); however, these components also block a portion of the visible light spectrum (wavelengths from 380nm – 420 nm) with a result that there may be a slight yellow appearance. This yellow appearance, not visible in single or thin multiple layers, may become noticeable when these materials are used in thicker or a greater number of multiple layers. This color should be considered in conjunction with color imparted by the glass itself.
There are also design considerations, which must be taken into account when a low e or reflective coating is used in the construction of a laminate. When the coating, applied to the glass substrate, is placed in contact with the PVB, the refractive index of the coating is changed and will result in a perceived color shift. This means that a coating in an IG unit may appear a different color than the same coating in a laminate.
Optical Distortion
Heat-Treated Glass
Images viewed in reflection from and by transmission through laminated glazing materials may be distorted. Both reflected and transmitted optical distortion may result from heat-treatment of glass, thickness variability of the materials used, mechanical stresses applied by the framing system and changes in exterior wind pressure and interior building pressure.
Laminated glazing materials may incorporate multiple plies of heat-treated (e.g. heat strenghtened, tempered) glass in order to achieve high levels of resistance to thermally and mechanically applied loads. Bow, warp and roll wave distortion are inherent characteristics of heat-treated glass. While fabricators take steps to minimize these conditions, they cannot be eliminated. All of these characteristics are accentuated by the use of reflective coatings and tinted glass substrates. Since transmitted distortion is dependent on overall thickness variability, it tends to be exaggerated by multiple plies of glass and other components. The thickness variations of the individual plies is additive. Laminated constructions incorporating annealed glass typically exhibit less reflective and transmitted optical distortion. Distortion in all glazing materials may occuras a result of glazing system, wind load pressures and overall bow and warp.
The visibility of reflective distortion is greatly affected by surrounding conditions and glazing orientation. If the reflected image is a uniform blue sky, the reflective image that appears in the laminated product may appear without distortion. If the same laminate is reflecting multiple gridlines from an adjacent building, the reflection may appear distorted. Roll wave distortion may be more visible by reflectance and transmittance when the direction of the wave pattern is glazed parallel to the jamb or vertical dimension of a window or door. In this application, images of lineal objects (such as building walls, utility and flag poles) and moving objects (such as cars and aircraft) become more visible as the viewing angle changes. In order to decrease the visibility of roll wave distortion in heat-treated laminates, fabricators commonly recommend and design professionals specify that the wave direction (wave’s peak) be glazed parallel to the sill of a window or door whenever possible. It is recommended that the manufacturer be notified in writing of these instructions prior to the onset of glass fabrication. Heat-treated glass fabrication equipment
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limitations may not allow roll wave orientation to the sill when the width dimension of a lite of glass exceeds the height dimension.
Multiple-Ply Laminates
Multiple ply glazing materials that include non–glass components such as interlayer films and/or plastics sheet products such as polycarbonate or acrylic sheet may also be a source of unwanted optical distortion. Special consideration should be given to these types of laminates.
Both glass (as previously described) and non-glass components may have thickness or flatness variability that creates lens effects, which may cause distortion of images when viewed through the glazing material. The magnitude and spacing of this variability are both important factors when trying to assess the suitability of a multiple-ply laminate for a given application as a precise alignment of the components containing this variability is not possible. Since this distortion is greatly affected by viewing angle, vertical lens lines are generally more objectionable
High performance plastic sheet used in multiple-ply laminates are most often either polycarbonate or acrylic sheet.
Acrylic sheet materials are produced by several processes, which exhibit varying degrees of distortion and thickness variations. Polycarbonate sheet is produced by an extrusion process, and therefore exhibits die lines (ripple direction) on both coated and uncoated polycarbonate, which may produce an objectionable distorted image. This distortion can be minimized by placing the ripple direction horizontal to the plane (when feasible) OR it is often preferable to orientate these die lines horizontally if possible. While plastic sheet manufacturers take steps to minimize these conditions, they cannot be eliminated.
Designers are recommended to further consider other conditions, such as: thermal expansion/contraction properties and changes in humidity, which may cause the plastic glazing material to bow, wan or warp; adequate space within frame systems to reduce perimeter issues due to edge pinch and, localized areas of distortion resulting from small particulate inclusions (fish-eyes) on coated plastic sheet materials. As more individual plastic layers are utilized in the laminate, distortion may become more pronounced.
Multiple-Ply Laminates incorporating both glass and polycarbonate components and their appropriate interlayer(s) are further described within ASTM C1349 Standard Specification for Architectural Flat Glass Clad Polycarbonate, and its Appendixes. Additional reference to the plastic sheet components and these types of laminates can also be found within the GANA Glazing Manual and the GANA Laminated Glazing Reference Manual. Refer to ASTM D 4802 Standard Specification for Poly (Methyl Methacrylate) Acrylic Plastic Sheet for the methods by which acrylic plastic sheet is produced and other specifications.
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Iridescence
When viewing laminated glazing constructions, under certain conditions, a pattern of iridescent spots or darkish shadows may become visible. This is commonly referred to as the strain pattern of the heat-treated glass and is related to the stresses introduced in the cooling process of the glass fabrication. While not normally visible, the strain pattern may become more evident by reflectance and in transmittance when viewing the glazing material at severe angles or under polarized light conditions. The potential of the iridescence becoming more pronounced is enhanced as the thickness of the laminated glazing material increases. The strain pattern is inherent in those heat-treated components and is not a result of discoloration or non-uniformity.
Product Awareness
As the design thickness of multiple plies of heat-treated glass and/or glass and polycarbonates increases to meet application requirements, the potential for distortion of images viewed through the glazing also increases. The bonding of multiple surfaces accentuates distortion as a result of the inherent variations in flatness of the component materials. Design professionals and building owners must be particularly aware of these characteristics in applications that involve viewing moving objects through the glass.
It is essential that design professionals consult with fabricators and suppliers in the early stages of design and engineering, given the sophisticated nature of laminated glazing materials required for optimum performance in safety, security, hazard resistant and sound reduction applications. Awareness of the laminated glazing product construction and inherent characteristics of the laminated glazing can dramatically affect the design application. Design professionals and building owners are strongly encouraged to utilize full-size mockups for evaluating the appearance of the glazing system under the specific project conditions, lighting conditions, and surrounding landscape. Utilization of a mockup is an inexpensive and reasonable process to ensure the product(s) and project design(s) meet a client’s expectations.
This bulletin was developed by the GANA Laminating Division – Optical Distortion Task Group and approved by the Laminating Division
– Technical Committee and GANA Board of Directors. This is the original version of the document as approved and published in October
2003. This edition of the bulletin provides the most recent update and published in July 2008.
