Once thought to be the work of the devil, glass is the treasure locked within the complex system of a leaded window. Every corner of design in regards to a stained glass window is intended to preserve this remarkable material. Fragile as it may seem, it is able to support a heavier vertical load than steel. Colored glass has been around since the ancient Egyptians and Romans. It could be found in Christian church windows as early as the fourth century.
Like many other facets of our industry, the art of glass manufacturing was not passed down generation after generation with great detail. With modern industrialism there has always been a desire to create a product cheaper and faster. This has resulted in glass containing less precious metals and more chemical makeup to create vibrant color. Glass produced in the Tiffany era contained rich alloys and minerals that lent the glass a beautiful "fire" that cannot be duplicated today by any modern glass manufacturer. Most glass today is made in large ovens and machine drawn, sometimes through rollers that can add texture. There are still studios making glass in the traditional sense, mostly in Europe where there is a greater need for mouth blown antiques. They blow glass vessels or cylinders. When reheated, they can cut them open lengthwise with shears and allow them to lay flat to create sheets.
Changes in the manufacturing process over the years have made it difficult to find perfect matches when repairing historic stained glass windows. This is one of the many reasons to retain as much original glass as possible when working with these works of art. Glass makers can often custom tailor a color for a client to match an old piece no longer in production. The quality of the match is never a guarantee and can be very expensive if only a small quantity is desired.
Another area of the industry that failed to be handed down was the techniques used for glass painting. There are extraordinary glass painters all over the world who still scratch their heads when they study historic painted pieces and wonder exactly how they were created. Painting on stained glass is often accomplished through lead based paints hand mixed by the artist, which can be applied as many different ways as their imagination might allow. After painting, the glass is fired in a kiln which essentially fuses the paint to the glass. Properly fired paint can be relatively permanent. Poorly fired paints and some enamels have been found to release from the glass due to heat and sun exposure. Repairing historical painted glass can be an extreme challenge and certainly not a task that should be attempted by anyone other than a highly skilled and educated artist.
When faced with broken pieces of painted glass or any historical colored glass, it is imperative that any and all original fabric must be salvaged. Wholesale replacement of these pieces is unacceptable. With the invention of modern adhesives this can be fulfilled in a fashion that has very little visual impact. However, when preserving historic works of art we try to make sure all our work is reversible as most epoxies and other such adhesives are not. We prefer to mend broken painted glass with thin strips of copper foil. The foil will be unnoticeable from several feet away and offer a water tight seal. Should the panels ever need future conservation work, they can be easily dismantled as not to cause further damage for future generations to deal with.