Stained Glass Window Maintenance and Repair

Sacred art is a profound expression of faith that helps engage the faithful in a deeper understanding of the mystery of salvation. As Catholics, we have a rich heritage of sacred art, and the most visible signs are the stained glass windows that adorn our churches. As with any feature of a church building, however, stained glass windows are subject to deterioration over time. Proper care and maintenance should be taken to protect and preserve these artistic treasures. 

[For basic information on how stained glass is made, please see the Khan Academy website.]

Periodic Inspections

It is good practice to periodically inspect windows and address any concerns in the early stages. “The longer you leave the repairs the more likely the deterioration will continue and then you are left with increased repair costs," writes Drew Anderson, a conservator with the Metropolitan Museum of Art who consulted at Saint Patrick’s Cathedral on behalf of the museum. He also recommends taking a photographic inventory of your windows periodically so that you will have a visual record of any changes. When assessing windows, look for the following:

  • Broken/cracked pieces of glass or pieces that appear to have slipped 
  • Faded paint
  • Moisture on sills from leaks
  • Excessive bowing (more than 1” out of plane) 
  • Broken tie wires on metal support bars that are in place to support the window
  • Rattling of the stained glass 
  • Peeling mortar
  • Condensation on the stained glass or in-between secondary glazing

Please note that if some of the conditions above are present, it does not necessarily mean there is a major problem. For example, some measure of bowing in windows is normal. Restoration architect Jean Phifer who consults with Murphy Burnham & Buttrick Architects, the design leaders for the renovations at Saint Patrick’s Cathedral in New York City, says, “As long as it’s stable and not getting worse you may decide to leave it.” At Saint Patrick’s Cathedral she and her team left a number of bowed, yet stable, windows in place. It is best to obtain the opinion of at least two reputable specialists before undertaking major restoration work.

Proper Cleaning

“Cleaning should always be carried out by a professional," writes Mr. Anderson. Ionized water (regular tap water) damages the glass, so conservators must use a pH neutral cleaner. Ms. Phifer adds, “Clean very gently, vacuum very lightly…every five to ten years if the windows are accessible.” Higher windows that require expensive scaffolding to reach can be cleaned every 20 years or so.  If the windows have paint details, the stability of the paint should be assessed before cleaning; some are too fragile for any form of cleanser. Windows that are too delicate to be cleaned have two options: repainting or conservation.  Mr. Anderson, while acknowledging that every case is unique, recommends a conservative approach that involves “… looking at ways to preserve what still exists and making sure any treatment is reversible.”  Trying to repaint or restore the original details can often lead to negative, unintended results that bear no resemblance to the original window.

Protective Glazing

Protective glazing greatly extends the life of stained glass windows in certain situations. Ann-Isabel Friedman, director of the New York Landmark Conservancy's Sacred Sites Program, describes it as, “…primarily a sacrificial layer to protect the stained glass from projectiles and direct rain and wind”. It is critical, however, that protective glazing be adequately vented to allow air circulation and that it be easily removable for future cleaning or restoration. Shoddy workmanship can cause more damage to the glass than it would have acquired without glazing. “It’s important to understand the function and purpose of the protective glazing and not just have a contractor come in and talk you into putting something in,” says Ms. Phifer.  She recommends taking the following into account when considering glazing:

  • Climate: seasonal changes in weather cause stress via thermal expansion/contraction
  • Threats: vandalism, hurricanes, sun exposure, acid rain, etc.
  • Accessibility: if windows are out of reach you will need scaffolding, which greatly increases the price of the project
  • Fragility: painted surfaces are more susceptible to deterioration

Complete Re-Leading Versus Partial Re-Leading

The lifespan of lead depends on the surrounding environment, but eventually it will have to be replaced.  “Tell-tale signs of a window in need of re-leading include bowing, buckling or sagging panels, tie wires loose from the structural support bars and significant movement of the window when pressed,” writes Mr. Anderson. Unfortunately, complete re-leading is one of the most expensive restoration projects. Ms. Phifer advises caution before committing to a complete re-leading of the window. “If one examines the window close up you can anticipate how much may be necessary,” she says. Once the panel can be evaluated in a studio, sometimes only a small part of the window needs re-leading. 

From a conservation standpoint, re-leading can also detract from the historical significance of the window. “A part of that value is the original lead,” says Ms. Friedman. “When you replace that lead…you’ve removed something original and in some way have devalued the window. You don’t want to be overly aggressive. You want to be conservative.” If you still suspect your windows are in need of new leading, Ms. Phifer recommends consulting with an independent conservator before hiring a contractor to undertake any work.  

Asbestos Concerns

Many caulk manufacturers used asbestos in their caulk formulas prior to 1970. Before a stained glass studio removes a window, an asbestos specialist must determine whether the caulking contains asbestos. 

If asbestos is present, the church should request a written description of how the stained glass studio will remove the glass and clean the site after removal. The plan should include a thorough vacuuming with HEPA vacuums. 

Hiring a Contractor

Due to the delicacy, value and importance of stained glass windows, you need to hire a dependable contractor with experience conserving the kind of windows you have. Ms. Friedman recommends looking for “…someone who will do a diagram and identify all the windows in the sanctuary by number, call out those windows that are in the worst condition and then offer or recommend some kind of phased repair.”  She advises avoiding a contractor that prices by the square foot or offers a wholesale for all windows.  It is “very rare for all windows to fail at the same time,” she adds.  Most churches do one or two windows every five years.

Properly caring for and maintaining stained glass windows does more than protect a slab of glass.  Ms. Phifer eloquently reaffirms the importance of these windows: “Stained glass is a wonderful artistic resource for churches.  I hope they continue to maintain and restore these remarkable historic artifacts…the quality, the light, the beauty of the color, if they tell a biblical story or depict saints…it’s very moving and important to not let them deteriorate.” 

© Bree Publishing 2015