Decorative Glass, Architectural Considerations
September 28th 2016, By Peter Ruplinger
Note: Peter Ruplinger is an artist, not an architect or engineer. This page is intended to provide information from an artist’s view of subjects related to decorative glass.
Unless indicated otherwise all photos and stained glass are by author.
Revised 27 May 2016
For public projects, it’s advisable to have a panel which includes several artist evaluate proposed designs. Surprisingly it is not unusual for developers to invest sizable sums for art that is not especially appealing. For example, a glass sculpture was placed in the lobby of Salt Lake City’s Abrovenah Concert Hall, that looks much like a pile of fish guts. A team of experienced art crytics can usually reccomend a design that most spectators will stop and gaze at. One way to define tasteful art is that people enjoy looking at it. When you see people stoping and staring at a piece of art, as though they were gazing right through it, you know it is fine art.
Art for private residences is easier. The home owners probably selected the stained glass artist or establishment because they liked their art. Architects and builders should probe the home owners for their specific likes. It helps to be observant of what art styles the home owners already have in their home.
Architects and builders need to consider what the customers want. Listen to them. This sounds elementary, but it is often too easy to choose a theme what appeals to the architect, designer or builder, not to the customer. Consider age, religion and interest. If it’s a private residence, look around the home and the customer’s interest will probably be obvious. Probe for what’s important to the customer. Don’t be surprised if they have no interest in art at all. Many people don’t, and there is nothing wrong with that. They may just want stained glass for the prestige, or to feel like their home is complete. That’s perfectly acceptable. Don’t hesitate to suggest new ideas that the customer may not have considered. Customer’s value a designer or architect’s creativity.
Obviously the stained glass needs to be cohesive with the architecture of the home or building. This requires flexibility and creativity on the part of the stained glass artist. As with all windows, stained glass fights the boxy constraints of walls. Look for the direction of movement in the Architecture. Balance of symmetry in lines an color instill a static mode. If the area is to be sedentary such as a restaurant, design the glass to be sedentary, for example with a central tree or pastoral theme. If the glass is positioned in a dynamic area such as a stairway, make the theme flowing. Obviously the design should be finalized at the project’s inception. Size and proportions should relate to the edifice scale. The design intensity, color quality, and color amount need to relate to the strength of the space provided.
Material Limitations and opportunities
Glass is surprisingly strong. A glass cube the size of a sugar cube ( 1cm x 1cm x 1cm) can endure over twelve tons without breaking. Furthermore, it is perfectly elastic. That means that when compressed, it always returns to its original shape. That, is of course if it does not break. It is brittle and can fracture without warning. If glass is to be more than decorative, engineering considerations for wind load and stress are necessitated. These factors will dictate the type and thickness of glass. Chapter 24 of the International Building Code (IBC) address the use of glass in buildings and residential edifices over three stories.
Despite limitations, glass is exceptionally versatile. There are colors, opalescent and iridescent surface coatings, and a myriad of shapes. Shapes may include; crystals, prisms, mosaics, wavy water like surfaces, textured surfaces, faceted surfaces, beveled edges, and more. Dalle de verre is an exceptionally beautiful style utilizing thick colored glass bounded with mortar instead of lead came or solder. Edges of the glass are hammered to form conchoidal fractures. Water-glass until recently manufactured by Spectrum glass produced an amazing water like illusion when placed before a light colored wall and illuminated from above. Obviously glass protects from the elements. Although usually considered transparent, it can also be strictly translucent. Ornamental texturing, including etching, carving and sand blasting, can allow light to enter, but diffuse and soften light to provide privacy. Colors create moods. Reds and yellows inspire warmth, thrill and excitement. Blues are known for coolness, safety, tranquility and peace.
Glass used in doors or beside doors is required to be tempered. Tempering is achieved by heat or chemical processes. Typically glass is pre-cut glass is placed in a furnace and heating to approximately 2,700 F. The glass is then gradually cooled. The result is glass with thin stressed skins on both sides. This improves bending resistance as much as seven fold in some processes. The added benefit, is that when it does break, it breaks into tiny pieces which are less likely to cause injury.
Glass Walkways and Stairs
An exceptionally beautiful application of stained glass is its use as stair treads and walkways.
Walkways and stair treads are typically fabricated with laminated glass. The binding lamination is typically poly vinyl butyrate. If the top lamination breaks, the lower laminations are rated to sustain the load. The top lamination is recommended to be certified as slip resistant by Underwriters Laboratories, or the National Floor Safety Institute. Cast slabs 1.5″ thick have a reported strength, when properly annealed, of 1,600 pounds per square foot. Walter Gordinier, in Portland Oregon, makes incredibly beautiful cast glass stair treads and walkways. His colors are spectacular. All glass, however is moderately easy to scratch and abraid. Glass has a hardness of 5 to 6 on the Moe scale. Sand, typically from decomposed granite, is significantly harder at about 7.5. The famed Gand Canyon glass walkway, needs to be resurfaced every year. This is done by replacing the 1/4″ top sheets of glass which protect the entire walkway. There is a film of water between the two. Obviously a residential stair tread will not see the abrasion of a major tourist attraction, but glass walkways and stair treads in public edifices would benefit with a protective glass overlay, or at least to be repolished routinely. The Grand Canyon glass stairway has approximately 370 thousand visitors each year. Based on their maintenance schedule, if a home were to have glass stairs accessed fifty times per day, the stairs could benefit from a polishing every twenty years. With new synthetic diamond abrasives, this would not be a difficult or costly project. Hardwood stairs would likely require a more frequent polishing.
Jose Sanches has written an excellent article which includes a section on the structure of glass walkways. See “Further Reading” below.
Consider the Location
Other factors to consider when deciding on an artistic style include the surrounding area, and culture. A shopping mall, transit center, campus, industrial complex, business district, park, inner city, or suburb might all deserve distinct styles of stained glass. Culture is especially important for art in public edifices. Art in south west America might necessitate an entirely different theme than art in New England. It is important to be sensitive to the feelings of all. Furthermore, in America, people sometimes even look for an opportunity to be offended and are quick to express their anxiety. An inappropirate theme might not only offend, but delay a project’s completion.
For both the architect, builder and customer, the budget is a good place to start. Remember that good taste does not depend on expense. If it’s a public edifice, planners probably established the budget well in advance. Determine if the budget should be fixed, or possibly flexible. Verify that funds are adequate for completion. Determine what the consequences may be if the budget needs to be exceeded. Consider what added splendor a more generous budget would provide. The artisan’s skill, technique, and possibly reputation certainly play a role in the budget. Below are examples of religious portraits. One is by Jim Berberich. Jim is probably our nation’s finest portrait painter. The other is by an unknown artisan using a very simple technique known as “stipple”.
What’s on the other side of the window?
Should it be hidden or seen? Don’t block a beautiful view with stained glass. If you need a design on the glass, but want to maintain transparency, consider clear glass with an outline that allows vision beyond. For example, an outline of birds, mountains. trees, or geometric patterns. Grisaille is a style of clear glass cut in geometric shapes. Windows frame both man made and natural beauty. Transparency opens up spaces allowing interaction with the outdoors while protecting from the elements.
Intricate Grisaille Style Window, Saint Michel, France
Complementing or Accenting
Ask yourself, “Is this glass to be the major center of attraction, or is it to help create an atmosphere”. For example a recent home oner wanted stained glass on a balcony over their dining/living room area. The center of attraction in this room was an enormous and elaborate marble fireplace. It was the first thing visitors would see entering the home. In this case, stained glass in the balcony should not detract form the fireplace, but lend a supportive atomsphere. In another case, a home owner wanted stained glass for their entry. They had a large fountain to the side of the entry, but the entry was definitely the center of attraction. The entry deserved a breath-taking, spectacular stained glass window.
Explore new solutions and techniques with existing and novel materials. Architects, Designers, and owners should work together to form an objective and explore creative ideas.
Establish a focal point which all lines will lead to. Often the best location is one third from either side, and one third from the top. The background should not detract from or clutter the focal point. Save detail and bright colors for the focal point. It helps captivate the viewer to have all glass pieces very slightly in color. Of nature’s four basic shapes, circle, cube, cylinder and cone, the least interesting, according to some, is the circle. On the other hand, Wright used it a lot in his stained glass. Space should be divided with variety, simplicity and harmony. Preparing the design usually entails numerous rudimentary sketches. Typically the final consideration is the frame.
Large scale projects demand simpler motifs. They are viewed from a greater distance. Busy, complex and involved subject matter is not appreciated. Large scale projects with multiple panels should have them that flow from one panel to another. Interwoven designs lend continuity.
Glass changes hue, density and tone with illumination. Glass in the studio may look noticeably different from installed glass. Even in the studio, stained glass will look different if sitting on a white piece of paper, held up off the table, held before a lamp, or held in front of a window. Glass will also vary noticiably with the lamps used. Low pressure sodium lamps are extremely yellow and grossly alter colors. High pressure sodium lamps are economical, but very yellow. Mercury vapor lamps tend
to be blue. Metal halide lamps are closest to natural sunlight when new, but as they age, they can vary from pinkish to bluish. Regular incandescent lamps are slightly yellow. Fluorescent lamps can vary from pinkish to bluish. Some fluorescent lamps provide a near daylight illumination. LED lamps can be most any color desired. Even with sunlight, stained glass may vary greatly depending on whether the glass is in direct sun, reflected sun, or shade. Colors in the glass will change noticeably as the day progresses. Consider orientation to the sun. It’s best to place a sample of glass in the actual location to test it’s appearance a different times of the day and night.
The glass above illustrates how different it may appear depending on the time of day.
There are four traditional methods for holding glass together:
Traditional lead channel is shaped like the letter”H” and called “came”. It has been in use for close to a thousand years, and is still often used. It is a costly technique and typically needs replacing every sixty to one hundred years. It does however, definitely supplement the impression of the era portrayed by the glass. Stained glass artist carefully consider the width and shape of came to be used.
Foil and solder:
Copper foil tape with solder is a system developed in the early nineteen hundreds. It is much easier to apply, and typically stronger. The foil has an adhesive backing. It is applied to the edges of each piece of glass. Then it is wrapped around so that it overlaps the front and back by about 1/16″. All pieces of glass are then butted up against each other, and soldered together. The solder can have a shiny silver like appearance, or with patina, can appear grey or black like traditional led. Patina should not be used on the solder joints of painted and kiln fired glass. It can destroy the paint. The foil method is usually attributed to Tiffany Studios in the early nineteen hundreds.
Glass laminates may be bonded with adhesives specifically engineered for the application. Bohle America Inc., is recognized as a leader in glass bonding adhesive technology. Silicone adhesive is not safety rated for glass, but is sometimes used when the decorative glass is silicone attached to a safety laminated double pain glass.
Glass laminates, with similar coefficients of thermal expansion (COE), may be fused by heating in a kiln to fourteen to fifteen hundred degrees. They must then be cooled for several hours or even days, depending on the thickness. The final result may be analyzed with a polariscope to detect areas of stress. Properly fused glass is structurally sound. Slabs of 1.5″ in thickness are reported to support 1,600 pounds per square foot.
Whether traditional stained glass is held together with came or foil, it should not occupy too great an area without bracing ribs to add strength. Bracing often consist of brass or zinc flat bar, 1/8″ x 1/2″. Bracing is especially important for glass in a door or skylight. As a rule of thumb, bracing should should not exceed spacing of eight to eighteen inches. The stained glass panel itself should typically not have a perimeter of over fourteen linear feet. This would mean, for example, a rectangle, no larger than: 1′ x 6′, 1.5′ x 5.5′, 2′ x 5′, 2.5′ x 4.5′, 3′ x 4′, or 3.5′ x 3.5′. Generally more bracing is needed near the lower portion of a panel than upper areas. Notice the bracing in the spectacular rose window below.
Joints in glass. if not strategically positioned may weaken the glass. When possible, without detracting form the design, joints should not form a linear path for flexing. Below are examples of a weak, and stable designs.
A weak joint may be strengthened by inserting a brass plated clock spring between the glass, at cross angle to the weakness.
Protection and safety
Stained glass is sometimes sandwiched between two hermitically sealed pains. This however, often becomes a maintenance problem. The pains will eventually leak. Moisture and mold may subsequently enter. Repair is difficult.
A better approach is often to have a double pained and hermetically sealed window on the exterior, and the stained glass placed up against it in a fashion that facilitates removal. If the installation is in a door, or a viewer accessible window, a pain of tempered glass should be installed in front of the stained glass to protect the stained glass, and personnel as well.
A strange quirk of modern man, is that many think the purpose of glass is to be broken. For example: When a minor electrical fire broke out in the Holy Grace Trinity Cathedral of Kansas City, after extinguishing, a well intentioned fireman broke out a large Tiffany designed window at the opposite end of the building to allow what little smoke there was to escape. The major source of glass destruction isn’t weather, it’s accidental, intentional, or vandalism. The less accessible stained glass is, the longer it is likely to remain.
Always consult a registered engineer for design specifications.
When possible it is best to formalize sizes and fabricate stained glass after edifice construction is complete. It’s not unusual for windows to be a different size than specified, and not even square. There is also the possibility of damaging the stained glass before the building is complete. In designing it is essential that the architect and stained glass artisan plan the window frames to accommodate mounting the stained glass. Below are examples of frames suited, and not suited for the addition of stained glass.
One of the marvels of stained glass is its’ classical lure. There will always be a love for stained glass designs especially from the victorian era. New technology has, however introduced some totally new designs. Technology used to digitally paint billboards can also be used to paint on the surface of immense glass panels. Screen printing can be applied to a polymer laminate sandwiched between two pains of glass. A serious concern with these new technologies is there durability. Traditional glass techniques, from as early as 1100 AD have proven to have a half live well over a millennia.
Chapter 24 of the International Building Code (IBC), produced by the International Code Council (ICC) sets out standards for construction in Buildings. The International Residential Code (IRC) sets out standards for residences not over three stories in height. Chapter 16 of the IBC, and section E-2751 of the American Section … for Testing Materals (ASTM) define acceptable loads on glass. V ult represents Ultimate design wind speed. V asd represents nominal design wind speed. Section 2409 of chapter 24 of 2015 IBC and section 11 of E-2751, both address glass specifically in walkways. However, they only addresses the use of laminated glass. Cast glass, now popular in stair treads and landings, is not discussed in current editions of the IBC or ASTM. The IBC and IRC are updated every few years. Keep in mind that many states use older versions and may alter building regulations to some degree as they feel appropriate. Furthermore, the code is not easy to interpret. It is strongly advised that professional and local assistance be acquired in applying the code.
Chapter 2 of 2015 IBC defines “Decorative Glass” as “A carved, leaded or Dalle glass or glazing material whose purpose is decorative or artistic, not functional; whose coloring, texture or other design qualities or components cannot be removed without destroying the glazing material and who’s surface, or assembly into which it is incorporated, is divided into segments.
Chapter 2 of 2015 IBC defines “Dalle Glass” (known in the industry as “dalle de verre”) as “A decorative composite glazing material made of individual pieces of glass that are embedded in a cast matrix of concrete or epoxy.”
Manufacturers of paving glass, similar to tiles, use the bridge loading design criteria established by the American Association of State Highway Transportation Officials. These specifications are sometimes broadly referred to “HS-20”
The American Architectural Manufacturers Association (AAMA) has published two easy to read articles on windows. Both are written by their consultant, Julie Ruth, PE.. They are well worth reading. www.aamanet.org/upload/file/IntlCodes_WD1213.pdf and www.aamanet.org/upload/file/CodeArena_WD0314.pdf
New Glass Architecture, by Brent Richards, Yale University Press, 1994
Adventure in Light and Color, by Charles Connick and Charles D. Maginnis, 1937
Glass Work: A Text Book for Students and Workers in Stained Glass, Classic Reprint Series, 2015
SGAA Reference and Technical Manual, Stained Glass Association of America, 2015
The Wright Style, by Carol Lind, Simon and Schuster, 1992
IBC Chapters 16 and 24
ASTM Section E2751
IRC Sections R308 and R610
Analysis and Design of Structural Glass Systems, by Jose Sanches, Instituto Superior Tecnico, 2013