INTRO TO STAINED GLASS:
The techniques used by today's artists to make a stained glass window differ very little from those used centuries ago by the medieval craftsmen who created the great windows of Europe's cathedrals. As a material glass is, simply put, melted silica (or sand) to which a flux (usually potassium) has been added. The colour of stained glass is determined by the addition of chemicals (usually metal oxides) and by the temperature and length of time the glass is heated. Glass with colour throughout its body is called POT GLASS or POT METAL.

Sheets of pot glass are produced in a number of ways. The first is the time-honoured method of blown glass, often referred to as ANTIQUE GLASS. There are a number of types of antique glass available to today's artists, including:


MUFF or CYLINDER GLASS:
Most commonly used form of stained glass. Produced by cutting off the end of an elongated balloon of blown glass that is then split along its length to form a flattened sheet. This method of making glass has been known since medieval times.

FLASHED GLASS (verre doublé):
A coloured, blown glass general composed of two layers of glass, one of which is white, yellow or blue. Flashed glass is obtained by two or more successive gatherings of molten glass at the moment of blowing. Flashed glass is often ETCHED using hydrofluoric acid that eats away the exposed layer of glass to reveal the glass underneath.

The nineteenth century witnessed a major revival of interest in ancient stained glass techniques. New types of glass were invented to meet the demand for stained glass windows in churches and houses. Many are still available today.

TIFFANY GLASS:
Patented by the American designer Louis Comfort Tiffany in the 1880's, this iridescent and opalescent glass is produced by the exposure of hot glass to metallic fumes and oxides.

CATHEDRAL GLASS:
Despite its grand name this is a commercially mass-produced, machine-rolled, clear or coloured, translucent glass introduced in the late nineteenth century. It was widely used in the United States and Canada during the late nineteenth and early twentieth centuries.

The most recent innovation in glass production is casting. Molten glass is scooped from the furnace and cast into moulds. When ANNEALED (or cooled) the slabs of glass are usually about 1 to 2 inches thick and about a foot long and often chipped or faceted on the surface. This type of glass, known as SLAB GLASS or DALLE DE VERRÉ, can be set into concrete, cement or epoxy resin and has become increasingly popular with modern glass artists.



MAKING A STAINED GLASS WINDOW:

To make a stained glass window the artist or glazier will first draw a small sketch of the finished work. Then, a full-sized design or CARTOON is made of the window. Using the cartoon as a template, pieces of glass in the appropriate colours and textures are selected and cut to fit the design. The pieces are then assembled and, if desired, painted.

When painting stained glass, the artist must take into account the effect that the colour of the glass itself will have on the finished product. The most common type of paint used is a brown/black VITREOUS ENAMEL PAINT, a powder of iron or copper oxide with a flux such as borax, used for shading and linework. Vitreous metal-oxide based enamel paints in various other colours may also be used but modern glass artists tend to employ these sparingly, allowing the glass itself to provide the desired colours. Another option for the artist is the addition of SILVER STAIN or YELLOW STAIN. This is a silver nitrate compound ground with gum and thinned with water, which produces a transparent yellow colour in varying degrees when fired onto the glass. Silver stain is often applied to the exterior surface of the glass since it fuses virtually permanently to the surface, while the less permanent vitreous paint is applied to the interior surface.


The painted and stained piece is then fired at relatively low temperatures (up to 1250 °F) to fuse the paints and stain to the glass without re-melting it. The pieces remain in the kiln for up to 15 minutes and are slowly annealed in the kiln. Much care must be taken at this stage to ensure that no cold draughts of air come in contact with the glass or it will crack or fly (shatter). Most painted glass needs repainting or refining since the vitreous paints tends to lose body during the firing process. With each successive firing the glass becomes more brittle.

Once the firing process is completed, the glass pieces are ready to be assembled, or LEADED UP, into the final window. The pieces are joined using CAMES made most frequently of lead which, being a very soft metal, adapts easily to the contours of the pieces. Viewed in cross-section the came looks like a sideways "H". The glazier inserts the piece of glass into each side so that the glass pieces are just touching the central core of the H. The cames are trimmed flush with the glass pieces. Tin solder is applied at the junction of each came. In the case of an exterior window the GLAZING COMPOUND is forced between the leading and the glass to make it watertight. The window is now ready to be installed.

For centuries the art of stained glass has been bound inextricably with its architectural setting. It is only in the last few decades that the stained glass panel has been seen as an autonomous art object. Although this development is still in its infancy, stained glass artists throughout the world - especially in Western Europe and Japan, as well as Canada and the United States - are striving to expand the traditional boundaries of their medium and injecting new ideas into this ancient art.

Suggested further reading:
Lee, Lawrence et al., Stained Glass*, New York: Crown Publishers, c1976
Reyntiens, Patrick, The Techniques of Stained Glass*, New York: Watson-Guptil, c1977
Elskus, Albina, The Art of Painting on Glass*, New York: Scribner, c1980

These books are available in the Canadian Clay & Glass Gallery Library and Resource Centre. The Library and Resource Centre is available by appointment only. To arrange an appointment, please contact the Administrative Assistant at the Canadian Clay & Glass Gallery.