Stained Glass Restoration
April 09, 2007
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Before considering restoration of a window, something about its construction must be understood. Essentially, stained glass is an arrangement of sections of glass set into an architectural framework. Traditional stained glass is not stained at all but is composed of glass that has been colored with metallic oxide while still in the molten state, thus called pot metal. The molten glass is then blown or rolled, and shaped into sheets that are later cut into segments conforming to a pattern laid out by the designer. These segments, e.g., a face or sections of a robe, receive detailing with vitreous paint, ground glass mixed with metallic oxides in a liquid medium. Such painting can be an extremely simple application of trace-line to indicate features, or the creation of three-dimensional effects using back-painting, matting, stippling, quill work, or scratching. The painted glass is fired so that the ground glass in the paint fuses with the surface of the glass, producing an image of great permanence. In the later Middle Ages, a yellow tint was introduced as a stain, which still required firing.
The many segments of glass are then joined together by narrow lead strips, called cames, that are fitted around the glass segments. The cames are then soldered at their joints and puttied to make them watertight. The sections of the leaded window must then be placed into a metal, stone, or wood window frame. Additional strength is provided by support bars (T bars) set in the frame of the window and thinner saddle-bars to which the panels of glass are attached.
With a proper internal survey in hand, it is possible to contact a restoration studio. Some firms are large, some smaller, but the key issue to judge is the process they propose. It is important to make sure that someone who has actually seen the window to be restored in place will retain responsible oversight for the entire process. The studio should respond to certain issues for each window:
» Evaluation of structural integrity of the window's support systems (leads, internal system of T bars and saddle bars, etc.) and proposals for reinforcement;
» Perception of structural integrity of the window frame (and possibly building);
» Cleaning procedures and materials; and
» Arguments on the pros and cons of external glazing.
Cleaning. Cleaning should never be attempted by amateurs. Windows have been severely damaged by well-meaning individuals using products that removed paint and exposed the surface to degradation. This does not mean that there cannot be cooperative arrangements. I have seen wonderful studios actually instruct individuals in the parish in cleaning techniques when the windows were deemed of sufficient stability and were not to be dismantled. The procedure used pure de-ionized water on soft cloth. The individual cleaning was very careful not to allow water to enter the puttied areas of the leads. Cleaning most commonly takes place in the studio during a larger restoration process.
Leading. It is not necessary to re-lead windows unless it is clear that the lead has deteriorated. There are medieval leads still being used in windows, and given protection and quality materials, there are American windows of well over 100 years old that seem as tight and well constructed as if they were made today. Many members of churches, however, in an effort to feel that they are "doing the job right" and not just a "partial restoration," have absorbed erroneous information that a quality job means complete re-leading. Windows that are sagging can actually be straightened under studio conditions. (They cannot be straightened while in place in the church.) Once returned to a flat plane, they may be able to be strengthened by additional supports, designed to accord with the window's form. Ask the studio specifically about which windows need re-leading and why; whether part of the windows need to be removed and whether others may remain in place. Ask that the studio actually point out the specific places where the leading shows its integrity -- or its need for replacement.
Repair of Broken Panes. A studio should be aggressive about urging a faith community to retain all elements of a window. There are methods of edge gluing and copper foil repair that are unobtrusive. Reject anyone proposing to discard original glass in favor of a new panel "in the style of."
Once a studio is called and issues are discussed, one question usually leads to another. Take good notes as these calls are made. It is possible to say, "We are looking at your bid and we have some questions about your evaluations of the frame. Can you explain a little more fully your suggestion that the sash needs to be replaced?" If only one studio suggests the sash be replaced, that studio might be right or it might be making a hasty judgment. Ask other studios for details about their determination that the sash does not need repair. These type of questions will help build up a sense of the "depth" of a studio's evaluation of the project.
Dr. Virginia Raguin is Professor of Art History at The College of the Holy Cross, Worcester, MA. Stained Glass: From its Origins to the Present (New York: Harry N. Abrams, 2003) and The History of Stained Glass: The Art of Light, Medieval to Contemporary (London: Thames & Hudson, 2003). She is also the editor of Catholic Collective, Catholic Reflection 1538 - 1850: Objects As a Measure of Reflection on a Catholic Past and the Construction of a Recusant Identity in England and America (Washington, DC: The Catholic University Press, 2006).
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