Few building materials have as great an impact on aesthetics, performance, and function as glass does. Yet, not all the different types of glass and their potential for being fabricated into different architectural components are as well-known as they could be. This course provides architects and other design professionals with an overview of the full range of possibilities available from glass manufacturers and fabricators. The intent is to provide a fundamental knowledge of glass manufacturing and fabrication as used in buildings. In the process, a design palette emerges based on architectural decorative glass that can help to create buildings that excel in all areas of design and performance. The principles and concepts covered are applicable to both new and existing building designs.
Photo courtesy of Pulp Studio
Architectural decorative glass is a versatile and varied set of products that can be used to enhance design in a wide variety of applications and building types.
GLASS OVERVIEW
Architects have been using glass in innovative ways for decades, in a wide variety of ways, since glass is recognized as being infinitely changeable and functional in design spaces. As a result, manufacturers and fabricators have been pushing the limits of glass technology to reveal its exceptional properties for decoration, energy savings, and functional uses for interiors, exteriors, and public spaces. Glass can help create an energy-saving facade with opportunities for bringing daylight and views into a building. The range of visual choices means that it can be used to enhance the aesthetic appearance of the built environment. In some cases, it is also strong enough to use for safety considerations, such as guard rails or balustrades. As an interior design element, it can be fabricated with complex curves, polished edges, and stunning digital graphics that complete the visual story of a space with the potential for privacy or transparency as desired. Some glass even provides fire safety possibilities based on its makeup.
Photo courtesy of Pulp Studio
Glass is used extensively in buildings to achieve different objectives, design intents, and performance requirements.
Trends in Glass and Glazing
Design professionals currently have access to an expansive array of different glazing products with different performance and design options. Computerized design coupled with performance modeling have facilitated the refinement of architectural glass being incorporated into buildings for appearance, performance, and benefit to occupants. The outcomes have been increasingly advanced and efficient solutions.
In recent years, glass manufacturers have been asked to respond to the needs of owners and architects to provide new and higher performing glass and glazing products to suit a range of design trends. While exterior glass has needed to respond to thermal energy concerns, interior architectural glass has been sought for a full range of design applications where thermal concerns aren’t an issue. For example, architectural glass has become a primary surface to add imagery such as signage, artwork, wayfinding, and displays. Similarly, glass has become a design element unto itself with clear, patterned, opaque, or textured surfaces that are used for partitions, balustrades, feature walls, and other design elements. Of course, larger glass sizes are sometimes required for these applications, meaning that thickened glass may be necessary to maintain appropriate deflection control. Additionally, the use of bent glass has been increasing to help to deliver architectural design objectives. Current technology allows for that without compromising the structural integrity of the glass.
The Significance of Daylighting
Another significant trend is daylighting in buildings, which refers to the illumination of buildings by natural sunlight. In an era in which we have become accustomed to electric lighting, it is easy to forget that for most of the history of buildings, natural daylighting was a critical influence on architectural form. The central elements involved in daylighting strategies have been–and continue to–be windows, skylights, and other openings in the exterior. It can also include interior architectural components that allow light to pass through instead of being opaque. If translucent glass is used, the daylight can be diffused, and glare may be avoided.
People have always been naturally attracted to light. Beyond its innate lure, numerous independent scientific studies have proven that daylighting is strongly correlated with substantial improvements in human health and performance. These benefits are fundamentally attributed to the visually invigorating and productive environments provided by natural light. Daylighting can also benefit building operations. From an energy use standpoint, natural daylighting may be able to replace electric lighting used within buildings for 70-80 percent of daylight hours, correlating with lower energy costs and reduced pollution from fossil fuel-based power plants. For buildings with air conditioning, reduced electrical lighting creates less internal heat, further lowering energy costs. Daylight can have other operational benefits, too. For example, glass skylights at the Union Square BART Station in San Francisco offers a functional walking surface above ground and a safe space below that allows so much daylight that it doesn’t feel like it’s below ground.
GLASS MANUFACTURING
Recognizing the ongoing and varied need for glass in buildings, we turn our attention now to the basic processes for manufacturing different types of glass. The main ingredient of glass is SiO2 (silica sand), which is a naturally occurring material. Hence, it is not surprising to learn that glass was discovered in ancient times in settings where SiO2 was subjected to high heat, such as a lightning strike, volcano, or very hot fires as used in the bronze age. As people started to intentionally create glass, a predominant technology was to use molten SiO2 to create a sheet of glass, or other shapes (i.e., for jewelry, containers, tools, etc.). As the notion of using glass in buildings for windows developed, hot sheets of glass were moved along rollers which created imperfections in the surface of the glass. If optical clarity was needed, then the glass would need to be ground and polished to produce parallel surfaces.
During the 1950s, Sir Alastair Pilkington and Kenneth Bickerstaff of the UK's Pilkington Brothers developed technology to create optically superior glass. In their process, a continuous ribbon of molten glass flows over a molten tin bath unhindered by the influence of gravity. The top surface of the glass is then subjected to nitrogen under pressure to obtain a polished finish.
Photo courtesy of Pulp Studio
Different types of float glass are manufactured in different sizes and makeups for distribution to glass fabricators.
Virtually all mass-produced glass for use in buildings today starts with the Pilkington process. However, since that process requires considerable investment to create the facility, the furnaces to heat the material, and the equipment to move and store it, there are only a relatively small number of actual glass manufacturing companies in the world. There are, however, many companies who purchase manufactured glass in bulk and fabricate it into products for use in buildings.
The process of glass manufacturing first involves collecting the raw materials needed, the primary one (70-90 percent of glass) being silica-based sand. This is a material found in great abundance on the planet, so it is not hard to acquire. The make-up and purity, however, can vary considerably from place to place. That means impurities, such as iron or other minerals, are commonly present. Other raw materials are used to enhance the physical qualities of manufactured glass. Sodium carbonate (Na2CO3, "soda") is a common additive used to lower the glass-transition temperature. Lime (CaO, calcium oxide, generally obtained from limestone), magnesium oxide (MgO), and aluminum oxide (Al2O3) are commonly added to improve chemical durability. This is the common formulation of “soda-lime” glass, which is based on mixing the correct amounts of each material together into batches ready for glass production.
Soda–lime glass for mass production takes the mixed batch of raw materials and heats them at high temperatures in glass melting furnaces. In a melted state, the batch is homogenized and refined (i.e., removal of bubbles) and the glass is formed. To create flat sheets of glass for windows and similar building applications, the Pilkington process is used–the molten glass flows from the furnace and “floats” over a bed of molten tin, where it spreads out to form a level sheet with virtually parallel surfaces. This process is generically referred to as creating float glass. In this basic state, it can then be processed further into one of three primary types of glass, each with different characteristics and traits as discussed further below.
Annealed Float Glass
This is the most produced type of glass for buildings. It is a basic product formed from the annealing stage of the float process, whereby the molten glass is allowed to cool slowly in a controlled manner until it reaches room temperature. This process relieves any internal stresses in the glass, which if not done, would cause the glass to crack with relatively little change in temperature or slight mechanical shock. Annealed glass is used as the base product to form other types of glass. It can be made from different raw material make-ups to address visual clarity or glass color. For example, clear or “low iron” float glass can be produced by using silica sand with little or no impurities from iron or other materials. This eliminates the common “green edge” color of conventional glass caused by iron in the sand, and ultimately, the glass. Other batch configurations can produce other color variations as well, which may be desired in annealed glass. It can also be manufactured readily in different thicknesses to address different strength needs.
Heat-Strengthened Glass
This is annealed glass that is subjected to a special heat-treatment up to about 680°C (1256°F), then cooled slowly afterwards. This process makes the glass twice as strong as annealed glass. If it does break, the fragments of the broken glass may remain in the frame and are usually large and more likely to stay together. While heat strengthening increases the mechanical and thermal strength of annealed glass, it is NOT recognized as a “safety glass” by typical building codes. Therefore, it is not to be used in balustrades or similar structural applications because of its limited strength compared to code recognized alternatives.
Tempered Glass
Tempered glass is at least four times stronger than annealed glass, making it more suitable for code-compliant glass facades, sliding doors, building entrances, bath and shower enclosures, balustrades, and other uses requiring superior strength and safety properties. When broken, tempered glass shatters into many small, regular fragments rather than long shards, which reduces the potential for major injuries. Tempered glass is annealed glass that is heated to about 700°C by conduction, convection, and radiation. Unlike the heat strengthened glass, the cooling process for tempered glass is accelerated by a uniform and simultaneous blast of air on both surfaces. The different cooling rates between the surface and the inside of the glass produce different physical properties, resulting in compressive stresses in the surface balanced by tensile stresses in the body of the glass.
Few building materials have as great an impact on aesthetics, performance, and function as glass does. Yet, not all the different types of glass and their potential for being fabricated into different architectural components are as well-known as they could be. This course provides architects and other design professionals with an overview of the full range of possibilities available from glass manufacturers and fabricators. The intent is to provide a fundamental knowledge of glass manufacturing and fabrication as used in buildings. In the process, a design palette emerges based on architectural decorative glass that can help to create buildings that excel in all areas of design and performance. The principles and concepts covered are applicable to both new and existing building designs.
Photo courtesy of Pulp Studio
Architectural decorative glass is a versatile and varied set of products that can be used to enhance design in a wide variety of applications and building types.
GLASS OVERVIEW
Architects have been using glass in innovative ways for decades, in a wide variety of ways, since glass is recognized as being infinitely changeable and functional in design spaces. As a result, manufacturers and fabricators have been pushing the limits of glass technology to reveal its exceptional properties for decoration, energy savings, and functional uses for interiors, exteriors, and public spaces. Glass can help create an energy-saving facade with opportunities for bringing daylight and views into a building. The range of visual choices means that it can be used to enhance the aesthetic appearance of the built environment. In some cases, it is also strong enough to use for safety considerations, such as guard rails or balustrades. As an interior design element, it can be fabricated with complex curves, polished edges, and stunning digital graphics that complete the visual story of a space with the potential for privacy or transparency as desired. Some glass even provides fire safety possibilities based on its makeup.
Photo courtesy of Pulp Studio
Glass is used extensively in buildings to achieve different objectives, design intents, and performance requirements.
Trends in Glass and Glazing
Design professionals currently have access to an expansive array of different glazing products with different performance and design options. Computerized design coupled with performance modeling have facilitated the refinement of architectural glass being incorporated into buildings for appearance, performance, and benefit to occupants. The outcomes have been increasingly advanced and efficient solutions.
In recent years, glass manufacturers have been asked to respond to the needs of owners and architects to provide new and higher performing glass and glazing products to suit a range of design trends. While exterior glass has needed to respond to thermal energy concerns, interior architectural glass has been sought for a full range of design applications where thermal concerns aren’t an issue. For example, architectural glass has become a primary surface to add imagery such as signage, artwork, wayfinding, and displays. Similarly, glass has become a design element unto itself with clear, patterned, opaque, or textured surfaces that are used for partitions, balustrades, feature walls, and other design elements. Of course, larger glass sizes are sometimes required for these applications, meaning that thickened glass may be necessary to maintain appropriate deflection control. Additionally, the use of bent glass has been increasing to help to deliver architectural design objectives. Current technology allows for that without compromising the structural integrity of the glass.
The Significance of Daylighting
Another significant trend is daylighting in buildings, which refers to the illumination of buildings by natural sunlight. In an era in which we have become accustomed to electric lighting, it is easy to forget that for most of the history of buildings, natural daylighting was a critical influence on architectural form. The central elements involved in daylighting strategies have been–and continue to–be windows, skylights, and other openings in the exterior. It can also include interior architectural components that allow light to pass through instead of being opaque. If translucent glass is used, the daylight can be diffused, and glare may be avoided.
People have always been naturally attracted to light. Beyond its innate lure, numerous independent scientific studies have proven that daylighting is strongly correlated with substantial improvements in human health and performance. These benefits are fundamentally attributed to the visually invigorating and productive environments provided by natural light. Daylighting can also benefit building operations. From an energy use standpoint, natural daylighting may be able to replace electric lighting used within buildings for 70-80 percent of daylight hours, correlating with lower energy costs and reduced pollution from fossil fuel-based power plants. For buildings with air conditioning, reduced electrical lighting creates less internal heat, further lowering energy costs. Daylight can have other operational benefits, too. For example, glass skylights at the Union Square BART Station in San Francisco offers a functional walking surface above ground and a safe space below that allows so much daylight that it doesn’t feel like it’s below ground.
GLASS MANUFACTURING
Recognizing the ongoing and varied need for glass in buildings, we turn our attention now to the basic processes for manufacturing different types of glass. The main ingredient of glass is SiO2 (silica sand), which is a naturally occurring material. Hence, it is not surprising to learn that glass was discovered in ancient times in settings where SiO2 was subjected to high heat, such as a lightning strike, volcano, or very hot fires as used in the bronze age. As people started to intentionally create glass, a predominant technology was to use molten SiO2 to create a sheet of glass, or other shapes (i.e., for jewelry, containers, tools, etc.). As the notion of using glass in buildings for windows developed, hot sheets of glass were moved along rollers which created imperfections in the surface of the glass. If optical clarity was needed, then the glass would need to be ground and polished to produce parallel surfaces.
During the 1950s, Sir Alastair Pilkington and Kenneth Bickerstaff of the UK's Pilkington Brothers developed technology to create optically superior glass. In their process, a continuous ribbon of molten glass flows over a molten tin bath unhindered by the influence of gravity. The top surface of the glass is then subjected to nitrogen under pressure to obtain a polished finish.
Photo courtesy of Pulp Studio
Different types of float glass are manufactured in different sizes and makeups for distribution to glass fabricators.
Virtually all mass-produced glass for use in buildings today starts with the Pilkington process. However, since that process requires considerable investment to create the facility, the furnaces to heat the material, and the equipment to move and store it, there are only a relatively small number of actual glass manufacturing companies in the world. There are, however, many companies who purchase manufactured glass in bulk and fabricate it into products for use in buildings.
The process of glass manufacturing first involves collecting the raw materials needed, the primary one (70-90 percent of glass) being silica-based sand. This is a material found in great abundance on the planet, so it is not hard to acquire. The make-up and purity, however, can vary considerably from place to place. That means impurities, such as iron or other minerals, are commonly present. Other raw materials are used to enhance the physical qualities of manufactured glass. Sodium carbonate (Na2CO3, "soda") is a common additive used to lower the glass-transition temperature. Lime (CaO, calcium oxide, generally obtained from limestone), magnesium oxide (MgO), and aluminum oxide (Al2O3) are commonly added to improve chemical durability. This is the common formulation of “soda-lime” glass, which is based on mixing the correct amounts of each material together into batches ready for glass production.
Soda–lime glass for mass production takes the mixed batch of raw materials and heats them at high temperatures in glass melting furnaces. In a melted state, the batch is homogenized and refined (i.e., removal of bubbles) and the glass is formed. To create flat sheets of glass for windows and similar building applications, the Pilkington process is used–the molten glass flows from the furnace and “floats” over a bed of molten tin, where it spreads out to form a level sheet with virtually parallel surfaces. This process is generically referred to as creating float glass. In this basic state, it can then be processed further into one of three primary types of glass, each with different characteristics and traits as discussed further below.
Annealed Float Glass
This is the most produced type of glass for buildings. It is a basic product formed from the annealing stage of the float process, whereby the molten glass is allowed to cool slowly in a controlled manner until it reaches room temperature. This process relieves any internal stresses in the glass, which if not done, would cause the glass to crack with relatively little change in temperature or slight mechanical shock. Annealed glass is used as the base product to form other types of glass. It can be made from different raw material make-ups to address visual clarity or glass color. For example, clear or “low iron” float glass can be produced by using silica sand with little or no impurities from iron or other materials. This eliminates the common “green edge” color of conventional glass caused by iron in the sand, and ultimately, the glass. Other batch configurations can produce other color variations as well, which may be desired in annealed glass. It can also be manufactured readily in different thicknesses to address different strength needs.
Heat-Strengthened Glass
This is annealed glass that is subjected to a special heat-treatment up to about 680°C (1256°F), then cooled slowly afterwards. This process makes the glass twice as strong as annealed glass. If it does break, the fragments of the broken glass may remain in the frame and are usually large and more likely to stay together. While heat strengthening increases the mechanical and thermal strength of annealed glass, it is NOT recognized as a “safety glass” by typical building codes. Therefore, it is not to be used in balustrades or similar structural applications because of its limited strength compared to code recognized alternatives.
Tempered Glass
Tempered glass is at least four times stronger than annealed glass, making it more suitable for code-compliant glass facades, sliding doors, building entrances, bath and shower enclosures, balustrades, and other uses requiring superior strength and safety properties. When broken, tempered glass shatters into many small, regular fragments rather than long shards, which reduces the potential for major injuries. Tempered glass is annealed glass that is heated to about 700°C by conduction, convection, and radiation. Unlike the heat strengthened glass, the cooling process for tempered glass is accelerated by a uniform and simultaneous blast of air on both surfaces. The different cooling rates between the surface and the inside of the glass produce different physical properties, resulting in compressive stresses in the surface balanced by tensile stresses in the body of the glass.
Specialty Glass
In addition to the three types of mass-produced glass, there are some specialty glass types that are produced, usually in small batches and using smaller, simpler equipment. These glass types are generally more appropriate for artistic or architectural glass applications with fewer requirements for safety or strength.
- Cast Glass is created with a “hot cast” surface texture produced by pouring and pressing molten glass onto or into a mold.
- Slumped or “Kiln-Formed” Glass is produced by placing float glass into a kiln over a mold having the desired shape or pattern and heating to the temperature where the glass softens and “slumps” to the form of the mold. The formed glass is then annealed and can be further processed or fabricated.
- Patterned Glass has a surface that has been imprinted with a texture or pattern at high temperatures while still in the molten or malleable state. It is also known as textured or obscure glass.
Whether mass produced or batch produced, the final glass products can be specified and selected by a fabricator to use in architectural building applications.
GLASS FABRICATING
As already noted, glass fabricators typically buy manufactured glass in bulk and then work with it in their shops to fabricate a range of specific architectural products. They often also provide the frames, supports, or other hardware items that are needed to install a glass product into place in a building. Different glass fabricators may have different capabilities or specialties such that not all products are available from all fabricators. Some serve a local market, while others are regional or even national. Some rise to the level of artisans capable of creating unique and exemplary artistic results for buildings that seek to incorporate that level of design.
Some fabricated glass products are fairly standardized, making them easy for architects to select and specify. In many buildings, however, standard products may need custom fabrication to fit into specific openings along specific paths of travel or other conditions. Collaboration with an architectural glass fabricator can help determine limiting factors, such as height limits for certain types of glass based on thickness and makeup. It is also appropriate to review the allowable tolerances for different glass products or installations including thickness, cut sizes, visual distortion, or other factors. Collaboration with a fabricator can also help identify opportunities for cost savings and design options that may not have been obvious.
Based on all the foregoing, the following sections review and address some of the common and available glass fabrications or processes added to manufactured glass.
Photo courtesy of Pulp Studio
Glass fabricating plants employ some well-developed and sophisticated processes to create final architectural glass products out of manufactured glass.
Chemically Strengthened Glass
Glass fabricators may determine that there is a need for strengthening a sheet of annealed glass that is different from heat-strengthened glass or tempered glass. Often, this is the case for a thin sheet of glass that is used for a specialty application but one for which scratch resistance and enhanced strength is important. The solution here is to chemically strengthen the glass, which is essentially a surface finishing process. It is carried out by submersing the annealed glass into a bath of molten potassium salt (potassium nitrate) at about 300°C (570°F). This causes the sodium ions in the glass to be replaced by larger potassium ions from the molten bath. In the process, it creates a much tighter and denser surface that is placed under compression and balanced by the inner core which provides compensating tension.
Generally speaking, this process makes the glass six to eight times stronger than untreated annealed glass. However, even though it is stronger than tempered glass, when it splinters, it still shatters in long pointed splinters like annealed glass. Therefore, it is not suitable for use as code-compliant safety glass. It is, however, quite strong even for very thin glass panels making it suitable for all other uses of glass, where added strength and scratch resistance are needed, such as use in elevator cabs, signage, etc.
Laminated Glass
In many cases, the use of two (or more) sheets of any of the three types of manufactured glass is undertaken to improve strength or achieve other characteristics. A glass fabricator can laminate the sheets together using a standard process. In between the layers, a clear, resilient material is added to add strength and keep the glass together if it receives an impact.
The interlayer material can be made from several readily available choices.
- Polyvinyl Butyral (PVB) is the most used interlayer with very good optical clarity, flexibility, adherence, and affordability. While suitable for most building types, it is not advisable to use it when it is exposed to moisture or water for prolonged periods of time since that may cause delamination.
- Ethylene Vinyl Acetate (EVA) is an alternative that is better suited for interior or exterior applications where the edges may be exposed to high moisture.
- There are also some proprietary interlayers available with a range of properties, but they may not be compatible with PVB or EVA.
- Interlayers can be clear, colored, patterned, or otherwise treated to create different architectural or artistic effects. Laminated glass offers many advantages, of which safety and security are the best known. Rather than shattering on impact, laminated glass is held together by the interlayer thus reducing risk of injury from shattered glass fragments and the security risk of glass breakage. In geographic locations where extreme weather events are a concern, laminated glass addresses wind and storm resistance as well.
Polished Edges
Sometimes a designer wants to achieve a very clean, sophisticated look using glass, (i.e., for handrails/ balustrades or other features where people will be close to them). Building code requirements can dictate laminated glass for this use, but if the edges of that laminated glass are exposed as part of the design, then special attention needs to be paid to those edges. The exposed edges on glass handrails are an aesthetic detail that shouldn’t be overlooked, so high-quality edgework is imperative for the integrity of the design.
Fortunately, some fabricators have the capability to provide a very precise, polished edge along all sides of a laminated product. Such precision avoids a less appealing aesthetic by providing a high-quality, zero-tolerance finish. This process can be applied to both tempered and annealed laminated glass with very good results.
Insulating Glass Units
Insulating units are two or more panels of glass bonded to a perimeter spacer material with a hermetically sealed airspace. The primary benefit is to improve thermal performance with better U-factors as well as solar control by influencing the Solar Heat Gain Coefficient (SHGC). All types of manufactured glass can be fabricated into an insulating glass unit. Coatings can be added in between the two panes of glass to adjust and fine-tune its overall properties according to project needs. Double glazed units are the most commonly used type of insulating glass unit, however in some climates, the use of multi-cavity, triple-glazed units is increasing in response to owner demands and tightening energy codes.
Coated Glass
Sometimes, there is a desire to add a coating onto one or more glass surfaces to improve the physical characteristics of the glass. There are two different ways to add coatings to glass.
- Sputter coating is a low-pressure technique that deposits a coating using a physical vapor deposition (PVD) method. Essentially, it uses a sputtering target that ejects material onto a substrate─in this case, the glass. This process is used in many industries, including computers and semiconductors. For glass, it can be done readily by fabricators since it does not require applied heat or unusual equipment.
- Pyrolytic coatings are incorporated into the glass by depositing microscopically thin layers of metallic oxides during the manufacture of float glass using a process known as chemical vapor deposition (CVD). Such coatings need to be applied by the manufacturer, but fabricators can purchase the pre-coated glass and use it to create other products. Having this type of hard pyrolytic surface fired at over 640°C (1200°F) makes pyrolytic products more durable than sputter coating. The pyrolytic process creates extremely durable coated products that can easily be handled, transported, and processed. In addition, because the pyrolytic surface doesn’t degrade like a sputtered coating, it can be warehoused locally for availability, reducing project lead times.
Coatings can be used to create glass with alternative visual properties such as color, opacity, light reflection, and absorption. Where needed, coatings can also produce low emissivity, solar control, and even self-cleaning properties. One common coating is “low-e” or low-emissivity coating for thermal purposes. This type of coated glass provides thermal control and enhanced insulation, as well as control of solar heat gain. Low-e coatings reduce the emissivity of the glass surface, meaning the glass provides greater insulation by reflecting heat back towards its source and can also be designed to absorb or reflect solar energy. As such, low-e coatings are useful for reducing both solar heat gain and heat loss. For a sense of context, uncoated glass has a typical emissivity of 0.84, while a low-e coated glass could have an emissivity of 0.15. This means only 15 percent of heat is absorbed and reemitted, while the rest is reflected. Different combinations of low-e coatings can be used in an insulated glass unit to provide the desired performance. Keep in mind, however, that low-e coatings, like most others, will have an impact on the color and amount of light transmission through the glass.
Bending Glass
While annealed glass is manufactured in flat sheets, some fabricators have the capability to bend and form glass in their facilities. Fabricators can form the flat sheets into a curved shape or profile using extreme heat and a mold or frame. This is most commonly done along a single axis, such that the sheet is curved in one dimension while the other dimension remains stable. In this manner, balustrades or other surfaces can take on shapes such as half-cylinders, waves, “s” shapes, or other curved appearances.
When a building design requires it, glass can also be bent into compound shapes, meaning both axes are impacted. Fabricated compound shapes can include conical sections, segments of spheres, ribbon twists, and even amorphic shapes─the only limitations are those imposed by the physics of the glass itself. The glass may be placed under heat and “slumped” over a mold in this case. Since these are clearly more complex and involve glass engineering as well as fabrication, collaboration between designers and fabricators is encouraged early in the design process in order to assure the design can actually be created at a cost within the budget.
All types of bent or curved fabrications can be made from annealed, heat-treated, or tempered glass and further fabricated into laminated or insulated units. They can also incorporate a variety of other features such as chemical strengthening and decorative treatments. These performance attributes make bent or curved fabrications suitable for a wide range of potential uses including exterior windows, curtain walls, store and mall fronts, custom residential glazing, interior partitions, display cases, cylindrical elevator enclosures, and skylights. They can also be used for decorative and artistic installations made of glass.
IMAGING TECHNOLOGIES ON GLASS
A common and growing design trend is to use glass as a material for graphics, imaging, signage, artwork, or other visual displays. Glass fabricators are able to provide such products as well, using a variety of technology options including the following:
Ceramic Frit
While this technique has been popular for architectural glass in the past, it is mostly used only for signage currently. The process involves permanently bonding a pattern of ceramic-based material onto the surface of glass. This has the benefit of durability, but its cost-effectiveness is limited to large projects with repeating patterns. Ceramic frit has some inherent limitations, too, namely a very limited choice of colors and significant size restrictions. It is also not favored if there are a lot variations in the pattern.
Flatbed Printing with UV Inks
An alternative to surface-applied frit is to print a pattern or signage directly onto the glass using UV inks. Note that these inks are cured with ultraviolet light (UV,) but that doesn’t mean they are UV-stable over time once they are installed in a building, particularly if they are exposed to sunlight. This process involves placing the glass onto a flatbed printer just like any other media that might be used on such a printer. The ink is applied with a print head that moves back and forth (similar to many common printers). The ink adheres to the glass, but it is not chemically bonded to the glass the way a frit application is. This limited adhesion makes the process suitable for signage but not for architectural elements. In some cases, though, it may be appropriate to print on the back side of the glass (i.e., #2 surface), allowing the printed image to be protected by the glass. In either case, the size of the printed area will be limited due to the size of the printer, further suggesting its preferred use for small graphic panels or signage.
Digital Printing with Ceramic Inks
This process takes the best attributes of the prior two processes. It is based on using ceramic ink that is applied directly to the glass surface using a machine similar to an inkjet printer. In this case, ceramic ink is applied and then fired onto the glass surface to make a more permanent bond. The size of a digital printer is larger than a flatbed printer, but there are still limits to the size of the graphics that can be placed. The process can be slower than some other processes since it is based on the speed of the inkjet moving across the glass. Nonetheless, there are some very positive attributes. These include the fact that the ceramic inks are UV-stable over time and tend to hold up well. The bonded ink makes it more suitable for architectural glass use since it is less likely to be damaged, with back printing of the glass still an option here, too. The visual resolution is also very good when using this process, although there may be some limits on the available colors that a printer like this can accommodate.
Images on Interlayers
For the best protection of an image and greatest versatility on content, a preferred approach is to print the image on material that can be laminated between two layers of glass. That glass can be annealed, heat strengthened, or tempered, and addressed like any other laminated glass product.
The first option is to use a photographic interlayer where a true photograph is the image printed on a film layer. That film with the image is then laminated between the glass. This process has the benefits of providing true photographic imagery consistent with the quality and resolution of the photograph. As such, things like color saturation and resolution detail can be very high and produce very satisfying results. Since different photographs can be used for different laminations, there is great flexibility in design allowing for images that don’t need to be repeated. This photographic process has some size limits restricting the width to less than five feet (approximately 57 inches). It is also recommended for interior use only.
The second option for putting an image in the middle of laminated glass is to print it directly onto a PVB interlayer using an inkjet printer with or without white and color. The printed PVB is then bonded between the glass layers in standard laminated glass style. This approach allows for larger image widths (up to 96 inches) and can be used both indoors and outdoors. It has good resolution detail, but there are some limits on certain color saturations (i.e., vibrant reds and true blacks). Regardless, it is a very versatile approach that allows for total flexibility in design for repeating or non-repeating patterns in small or large quantity production. If multiple interlayers are present (i.e., three or more layers of glass), then multi-layering of the images is possible, or the image can be combined with a diffuse layer for more interesting effects. Since the materials are standard for laminated glass, this process can be used with any glass type, as part of an insulated glazing unit or in any other common glass lamination application.
CONCLUSION
Architectural glass serves many purposes. Starting with any one of three manufactured products, glass fabricators can create standard and custom products that are functional, decorative, protective, and safety conscious to suit individual project designs. Working with a fabricator during the design process helps building designs become realized and that consider the full range of possibilities and options while meeting cost and performance objectives.
Glass Surface Treatment
Separate from printing images onto or between glass surfaces, it has also been common to create an image by etching the surface of the glass. Artistic, decorative, and informational images have been routinely created this way which include logos, signage, and visual aid assistance.
The etching process can be done any of three common ways. First is acid etching, which relies on a chemical process of acid, removing a portion of the surface of the glass and creating a rougher, unpolished surface. The placement of the acid is very controlled, using a pattern or covering that only allows the etching to occur where intended and thus creates the desired design. A similar approach is to use focused sandblasting to roughen up the surface of the glass either in a prescribed pattern or across the entire glass pane for a diffused light effect. For very precise patterns, images, or other markings, laser etching can be used which simply uses a guided laser to remove a small part of the surface of the glass. Any of these techniques can be used to create a translucent image that will be a durable, permanent mark in the glass. That makes them suitable for indoor applications, such as partitions and doors, or outdoor features, such as exterior murals, sculptures, and walkways.
Peter J. Arsenault, FAIA, NCARB, LEED AP is a nationally known architect and a prolific author advancing positive acoustical experiences through better building design. www.pjaarch.com, www.linkedin.com/in/pjaarch
