Protective Glazing

Protective Glazing for Stained Glass Windows?

Consider Well!

Stained glass windows can add beauty to a church’s sanctuary that enhances the reverent worship that takes place there. Every pastor and parishioner cherishes such windows…and they also want to take good care of them. Because of this, protective glazing (or coverings) for the windows are often considered as “sound investments.” Many professional stained glass conservators, however, do not share that opinion.

In an article printed in the February 1987 issue of Professional Stained Glass magazine, Julie L. Sloan, one the foremost authorities in our country on stained glass conservation, asks in the title, “Protective Glazing: Is It Necessary?” Her thesis is that “even though it is heavily promoted by studios eager to earn a quick profit, protective glazing is usually not only not necessary, it often creates more problems than it solves.”

Three reasons (Sloan calls them “scare tactics”) often given for the need for protective glazing are: air-pollution, vandalism, and energy conservation. She points out that the need created is most often non-existent.

Take the case of air pollution. Recent studies show that 20th century glass is “virtually impervious to most forms of air pollution.” As for the lead, it is actually aided by pollution to form a protective surface of lead sulfate.

The second concern, vandalism, is one reason for breakage and damage to glass and lead. Glass may also break from age or stress, however, which is not hindered by any form of protective covering. Protection from vandalism may be achieved in a variety of ways, furthermore, many of them less expensive and more practical than glass or plastic coverings.

“…protective glazing is usually not only not necessary, it often creates more problems than it solves.”

Energy conservation is certainly a concern for churches, and stained glass windows are often cited as major culprits in energy loss. When putty and lead break down, the windows become drafty. However, there are other factors involved in energy conservation that ought to be considered as well. Large spaces–such as churches–will, in time, establish a balance in temperature and humidity. This balance must be taken into consideration when protective glazing is proposed. This is especially true of churches that have large pipe organs that may be adversely affected by radical temperature and humidity changes. Furthermore, as Sloan suggests, a building committee might have an infrared photograph taken of the building before they approve the great cost of protective glazing. The photo may show greater heat loss through an un-insulated roof, for example.

Having said all of this, the biggest problem has not yet been addressed. What is that problem? Simple water. And here, the proposed solution may contribute to the most serious problem. “Water is the worst enemy of stained glass windows,” says Sloan. It literally eats away glass and lead, and rots wood. Furthermore, Sloan adds, “A dangerously wet situation is not often found in an unprotected window, but is frequent in windows whose protective glazing is not adequately vented” (emphasis mine). Even in well-ventilated windows, protective glazing prevents the regular “washing” of windows by rain that can remove hygroscopic (water-attracting) dirt.

A large stained glass studio that installs protective glazing confirms these considerations. Quoting from one of their advertising newsletters, they caution, “Beware! Improperly vented protective glazing can create more damage than vandals tossing rocks.” A good portion of the brochure then goes on to describe how they restored a church’s stained glass windows that actually fell out of their frames due to deterioration caused by improperly vented protective glazing! The studio’s newsletter continues, affirming“The main cause of deterioration to stained glass is water.” They describe the exact same problems that Sloan raises in her article, then conclude, “Thus, an unprotected window is the better choice over a poorly designed protective glazing installation.”

And this is from a studio that advocates protective glazing! Of course, they offer a “better designed” protective glazing that is properly vented. And to their credit, I believe that theirs may be better, due precisely to their ventilation design. However, the cost for such protective glazing is immense. Why spend huge sums of money for something that is almost always unnecessary? A church would do better to take the thousands of dollars (often tens of thousands) that they would pay for protective glazing, put it in a savings account, and use the interest to pay for the regular maintenance of the windows–which must be done, anyway! The above quoted stained glass studio confirms this when they add their own disclaimer: “Note!” they say, “Protective glazing alone is not a restoration technique of stained glass or an alternative to proper maintenance of stained glass (emphasis mine).

It should be pointed out, also, that no protective glazing will stop deterioration. At best it can only slow it down, assuming that it doesn’t speed it up through improper installation. If a church has protective coverings–old or new–the parishioners would do well to have them inspected to insure that they are properly ventilated. If not, they may be courting bigger problems. In the end, regular, preventive maintenance of stained glass is the best way of preserving and keeping up valuable windows.

The final consideration for coverings has to do with aesthetics, or how it will it affect the window’s beauty–which is the reason why the windows were made in the first place. Stained glass windows have always been designed and made to be openly exposed. They have lasted for centuries and have been enjoyed by millions of people in this way. Covering windows in any way only covers their beauty. It is most unsightly to pass a beautiful, Gothic church, for example, that has its windows covered with plastic, giving it a “blind” look. When covering is necessary, the method that least covers their beauty should be sought. The best method to protect stained glass is a fully leaded protective glazing. In this method, the essential lines of the original leaded window are reproduced in lead to maintain the original appearance of the exterior of the building. This method is also the most costly (but may be comparable to properly vented, plastic coverings). Other methods each have their advantages and disadvantages. In the end, all factors–such as cost, maintenance, beauty, and actual protectiveness–must be weighed.

If window protection is needed (which is usually against vandalism), the most economical choice is plain wire mesh. This is the preferred method in Europe, by the way, where stained glass windows–and their maintenance–have existed for centuries. Wire mesh protects against most kinds of vandalism is usually less visible than plastic coverings, allows for rain washing of the windows, and is a fraction of the cost to install compared to other methods. A local contractor could probably do the job.

If a congregation is considering protective glazing for its windows, consider well. First, whether it is necessary. Secondly, for what reasons. And finally, what method will best fit the needs and the finances to protect her beautiful and valuable stained glass windows.


William L. Gleason