Material Matters

Ruby, emerald, amethyst, amber; the sheets are lined up on my easel. In a ritual as old as stained glass itself, I am choosing the glass for a new window. The colors are vibrant in the sun; the light majestically transformed by its passage through these thin plates of glass. Looking at the sheets, I see in each the tale of its making - its origins in sand and metal oxides, the tremendous heat that turned these elements into glowing liquid; and the pressures that shaped the cooling mass. A closer look reveals a bubble half-formed; a stress line; a sheen of color thickening, then thinning against its background.

It is here, in the planning and choosing of materials, that glass artist and craftsperson are one. It doesn’t matter how beautiful a design looks on paper, the window will only succeed when the materials are right. Looking at the glass on the easel, I consider the color, texture, and character of each piece, as well as how it will respond to any treatments - painting, etching, sand-blasting, silver staining - that it will undergo. Each piece must be the right one for its location - able to work both on its own, and in concert with those that surround it.

During the creation of the rose window for St. Andrew Church in Columbus, Ohio, I waited until all of the other colors were in place, up on the easel, before I looked for the right red to use for the center. I had many sheets of fine, hand-made red in stock and pulled them out one by one, judging them in relation to the surrounding blues. Eventually, I pulled out a small sheet of very expensive (and now unobtainable) English-made streaky gold ruby glass, which I had been keeping for fifteen years. I knew right away that it was exactly the right red. It had a depth and richness that none of the others possessed, and it alone could hold the center amid a deep blue window set in stone tracery. I must admit that I didn’t want to use it. Not only was this glass irreplaceable, but it was 3/8" thick with a 1/8" flash, which meant that it wasn’t going to be any fun to cut, paint and fire. Of course we did use it; and now, seeing that piece glowing in the center of the window, I don’t regret it.

Looking at a supplier’s catalogue, one could be forgiven for thinking how lucky glass artists are, to have such a wide range of materials to choose from. In one sense this is true; glass is sold in an incredibly wide range of colors, textures, and degrees of transparency. However, much of what is available in North America is machine-made, and although these processes produce some interesting textures, for the most part I prefer to use hand-made “antique” glass.

(Footnote: The word “antique” refers to the process by which the glass is made, not the age of the glass.)

With few exceptions, the history of glass making has been one of increasing efficiency, with greater evenness, clarity, smoothness and size of sheets - culminating in modern float glass, which, while a technical marvel, is so characterless as to be nearly invisible. Not surprisingly, glass artists gravitate towards materials made with the older methods, with the textures, imperfections and incomparable colors that they bring. These bubbles, striations and uneven surfaces have the effect of trapping light in the glass, and giving it a higher luminosity and shimmer.

There are several techniques for producing hand-made stained glass. In the most common technique, called “muff” glass, the glassblower begins by gathering a knob of molten glass onto the end of a blowpipe. This knob, or “gather”, is blown and shaped into a long, hollow cylindrical shape. The glassblower then removes the ends of the cylinder, makes a cut down its side, and reheats it, allowing the cylinder to open up and flatten into a sheet. This sheet is then annealed; that is, heated and cooled to relieve the stresses in it. The glass that results is indeed a record of its making, showing the ripples and bubbles of the molten liquid that it once was.

Many techniques are used to enhance the beauty and character of the glass during and after this process. Color is produced by dissolving metal oxides, sulfides and other substances in the molten glass. Other colorants may be dispersed as microscopic particles. The coloring process used can make a significant difference in the cost of glass. Fine particles of gold are sometimes used in making ruby or pink glass - and the price reflects this precious ingredient.

As glass is made it can be textured, layered, striated and molded, to achieve some wonderful effects. Some of the available kinds of antique glass are:

Streaky - made by mixing glass of different colors in one batch. Streaky glass is rich with a play of color that comes to life with light and the moving eye. Because it is so visually active, streaky glass is one of the most difficult to use. Compositions that use it have to take into account the movement and character that the material itself will bring.

Flashed - This glass is made by dipping the hot gather into molten glass of another color, resulting in a thin layer of that color on the base glass. Hand-made flashed glass offers unending possibilities to the artist. Depending on the flash, the color can change or even disappear across the surface of the glass, and the patterns and shapes thus formed can be used in concert with the design to give a painted quality. Alternatively, the artist can place a patterned resist on the flashed side of the glass and remove the flash by sandblasting or acid-etching to allow the base glass to show through.

The most common type of flashed glass uses a transparent base, with a coloured flash. Red glass is almost always flashed, because a solid sheet of red is too dark for many applications. Thus, red is flashed onto a variety of base colours: white, yellow, pink, blue, grey - even green. Opak is created by flashing white onto coloured antique. As the name suggests, the result is nearly opaque. Opal glass appears as a translucent skin of light - a pearl-like finish flashed onto clear or coloured glass. Used as a design element, opak and opal glass can provide privacy in interior settings. In exterior windows, this glass seems to catch and hold the sun with a magnificent glow, at the same time keeping the color from flooding the interior.

Seedy - This type of glass contains numerous air bubbles, which can be achieved in different ways. One way is to pull the glass from the kiln before the air bubbles have been released by time and heat. A more interesting way is to toss an organic material, such as a potato, into the molten glass. The material vaporizes, and the reaction produces air bubbles. (Canadian glass artist John Wilcox reports that he uses garlic - much to the dismay of his studio colleagues!) Whatever way it is made, seedy glass brings a unique texture and variety to a window. In the sun the bubbles shine like jewels and the visual texture changes constantly with the movement of the light.

Reamy - This glass is made by mixing glass of different hardness in the same batch. The result is a surface textured with waves and ripples, like the frozen surface of a pond. Because of the varying thicknesses in a single piece, reamy glass can be tricky to cut. As well, care must be taken in the orientation of the glass, to maintain the “flow” of the texture from one piece to the next. The rich surface effects make the effort well worth it.

Crown glass - This glass is made by spinning a glass bubble on the end of a rod, and cutting one end open to allow the bubble to open into a large circular sheet, or rondel. The central knob, where the rod was attached has a characteristic “bull’s eye” look

Bevels, jewels, prisms and lenses - This glass is made by pressing or casting glass into a mold. This method is also used to produce modern versions of crown rondels and bull’s eyes.

Machine-made glass is much cheaper and much more widely available than hand-made glass. Among the machine-made glasses, “cathedral” glass is perhaps the most common in North America. Made by flattening molten glass with textured rollers, this glass has an even color and thickness, and the rollers produce its characteristic texture. Cathedral glass is often used in commercial applications where something more colourful than plain glass is desired, but where cost is a major consideration. It has also been extensively used for domestic windows (transoms, door panels, etc.) and in church windows done in the Victorian revival style, where its even, characterless colour provides a neutral background for the heavily painted windows. American opalescent, used extensively in Tiffany-style windows and lamps is another machine-made glass. Tiffany himself created sculpted glass sheets of intriguing beauty and depth. Some contemporary manufacturers are working to recreate this unique glass.

Semi-antique glass, which is also called “drawn” or “new” antique glass, mimics some of the character of hand-blown glass, while providing a relatively consistent medium for the craftsperson. It is more interesting than cathedral, and its lower cost and wide availability make it suitable for a variety of applications. However, its consistency - while handy for the craftsperson that is cutting and leading it - also robs it of character. The very restricted palette of color is also a limitation in using this glass.

A glass artist is constantly aware of materials. Even in my initial discussions with clients, I need to think about the type of glass that will be required. Some of it will already be in my racks (I make it a point to buy interesting sheets whenever I see them). The rest, I will get from my suppliers. After I have gathered a selection of sheets, I arrange them on my easel and begin to choose. It is here that the glass begins to shape the window, as I see how a particular pattern or shading in a sheet can be used to enrich the design. In some cases, I will adjust the design to bring out this unique element.

There are many ideas about how and where different types of glass should be used. As an unabashed advocate of antique glass, my first choice is always something that hands have made; I love antique glass for its incredible variations, for its depth, the quality and variety of colour, and for the interesting and evocative effects that can be achieved with it. At the same time, I see the value of what other types of glass can bring to a window - to provide a contrasting texture, to tone down a section, or in the case of prisms, to catch the light and send it in coloured bands across the floor. I also delight in seeing how other artists use glass, in all its variety.