How Stained Glass Works

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­Even though man-made glass beads can be traced back to the ancient Egyptians and Romans, and a few surviving fragments of stained glass pieces can be dated to the ninth century, the first detailed description we have of stained glass as an art form comes to us from Theophilus, a 12th-century monk. Theophilus describes glass-making and the creation of stained glass windows in his work, "On Diverse Arts." A number of chapters in his treatise are devoted to stained glass window construction and show us the keen interest in the topic that must have existed at the time [source: Metropolitan Museum of Art].

The growing popularity of Gothic architecture, with its ability to support large, heavy stained glass designs, helped usher in a new period. Stained glass windows in churches across Europe got bigger, more complex and more majestic in the mid to late Middle Ages. It's from this period that we see many of the most masterful examples of stained glass in existence today [source: Metropolitan Museum of Art].

Changes in political and religious beliefs had a profound impact on the development of stained glass, as well as on the survival of the stained glass artwork in churches across Europe. The­ Protestant Reformation in early 16^th-century Europe, the rise of Oliver Cromwell in England and the French Revolution all brought upheavals that resulted in the wanton destruction of religious art, including many irreplaceable stained glass windows. After these episodes of unrest, glass artisans sought less controversial, more lucrative work with wealthy patrons, and eventually began using more nonreligious subjects, like nature or heraldic themes in privately commissioned projects.

There have also been artistic shifts in the style and popularity of stained glass over time. The Renaissance painters of the 15th century introduced a trend toward more subtle and realistic images in art [source: Morris]. As a result, glass artists began painting on glass rather than relying heavily on colored glass and lead framing to create images. This gave them more of an opportunity to create fine detail in their work. But as a result, some of the power, brilliant color saturation and bold structure of stained glass design was lost in the process. By the beginning of the 19th century, many of the basic techniques of coloring and texturing glass had been abandoned, and stained glass had lost much of its popularity.

There was a resurgence of interest in the old ways of making and u­sing stained glass during the Victorian Gothic revival of the 19th century [source: Morris]. Men like J. R. Clayton, Alfred Bell, Charles Eamer Kempe, Louis Comfort Tiffany and William Morris began to rediscover stained glass techniques and bring new modernistic designs and innovative materials to the medium. One such advancement engineered by Louis Comfort Tiffany was the introduction of a copper foil construction method that made assembling stained glass designs and working with curves much easier. Stained glass art objects like lamps became popular, and new uses for stained glass in public buildings and private homes help usher stained glass into the 20th century.

Now, the widespread availability of colored glass and glass cutting and shaping tools makes it easy for even novice artists to create with stained glass. Professional stained glass artists can look to new trends in modern art and the use of unexpected materials, like mirrors, to drive innovations in the stained glass of the future. Some of the limitations imposed on large stained glass pieces, like the need for strong, visible supports, may be changing too. New ways of strengthening stained glass artwork with processes like laminating are making it easier to construct bigger stained glass designs without additional bracing.

­Although glass itself is a naturally occurring substance and has color variations as a result of impurities, man-made glass was probably first created accidentally as a result of the high temperatures used in making pottery. To make glass, silica and other materials are melted and fused together. Silica (sand) melts at 3,000 degrees Fahrenheit (1,650 degrees Celsius) requiring the use of a glasshouse pot or kiln [source: Valldeperez]. The formulations, or recipes, for stained glass can vary from artist to artist but always include silica and substances like boric acid, lime, caustic soda and potash to strengthen, stabilize and help the stained glass ingredients melt uniformly at a lower temperature than silica alone.

Color is added to the melted silica using ground metal oxides. Once these coloring agents have been added to the molten glass, or gob, it's refired. The colored glass can then be manipulated in any number of different ways to achieve a specific result, like shaping or texturizing.

­These m­anufacturing practices have changed over the last thousand years, been lost, rediscovered and refined. Although there are still closely kept secrets to the glassmaker's art that each artist protects, there are some basic methods of creating glass that we should take a look at:

Blown glass - Also called cylinder and antique glass, blown glass is made by using a blowpipe to create a glass cylinder that's then cut and annealed, or cooled, slowly. This is the old-fashioned way of manipulating glass and has been around for almost a thousand years [source: Vallde­perez]. Because the thickness of the glass isn't uniform, the finished glass sheet has variations in color and small imperfections like the presence of bubbles. Blown glass is made in smaller batches than other glass-making processes and is one of the most popular types of colored glass.

Table glass - Known as cathedral glass and rolled glass, table glass is created by spreading molten glass onto a metallic working surface and then rolling it into a sheet.

Textured glass - Created by rolling, textured or pressed glass is made in a way similar to table glass, but a distinctive pattern or texture is worked into the glass as it cools. The result is less transparent but catches the light in unique ways.

Flashed glass - One of the historical disadvantages of vividly colored glass was that it tended to be opaque. Flashed glass was designed to solve this problem. Clear glass was coated with colored glass, originally red, and then cooled. The resulting glass was a sandwich made up of clear glass between two very thin layers of red glass. This veneer was colorful and highly transparent. The red could then be sanded or removed with acid to create different hues.

Molded glass - Glass can also be made using a mold to create shapes and distinctive concentrations of color. Rondels and art glass cabochons are created this way.

There are also a number of other types of artistic glass used in stained glass design. Opal glass and interpretive glass, like the style developed by Louis Comfort Tiffany in his famous decorative designs, are also popular for their unique appearance and refractive qualities.

Next, we'll take a look at the tools used in making stained glass.

There are a number of important steps in the process of making stained glass designs that focus on both artistic and structural goals. Creating a work of stained glass requires attention to detail. It also requires a plan, specialized tools and space.

To recreate the illumination that will make a stained glass creation come­ to life, stained glass artists employ a light table. They also use areas for cutting and assembly. A glass worker's studio will usually offer lots of natural light to work with and have sturdy storage for completed glass pieces and for colored glass used as raw material.

No tool is more important than the glass cutter, and choosing the best cutter is often a matter of personal preference.

Carbon steel glass cutters have replaceable tips and short handles that make it easier to make accurate cuts. Diamond glass cutters are a little trickier to use, but have no problem cutting even very hard glass. To make round cuts, a circle cutter is often used. It works by rotating a cutting arm in a circle around a suction cup that holds the tool firmly on the piece of glass. A glass artist will probably keep a variety of cutters on hand for different projects.

Glass artists also use a number of other tools, like pliers and a grozing iron to remove small burrs and jagged pieces from cuts, and pattern shears that help cut accurate glass pieces that will fit into the design. These shears take the guesswork out of cutting the perfect sized piece of glass.

After cutting a piece of glass, the stained glass artist will refin­e and smooth the edges with a number of abrasives and brushes. First, the edges of the glass must be polished with a silicone carbide block, diamond sanding paper or an electric grinder. Then the piece is brushed clean.

After cutting and sanding, the glass pieces are laid and evaluated for accuracy and color. The pieces are then reassembled using copper foil or lead cames, H-shaped strips of lead that hold the glass in place, going together like the pieces of a jigsaw puzzle. This latticework of metal is soldered together, and then putty is added to keep the glass from shifting.

To complete the process, the stained glass, if it's in the shape of a window, must be installed. It's fitted to a frame, usually made of wood or aluminum, sealed and then set into a window opening. For additional support, crossbars are sometimes set in place to keep the window from sagging. Stained glass can get heavy, so for large pieces, copper wire is often soldered to the cames and then wrapped around the supports.