Preserving the Heritage of Stained Glass
With proper stewardship, a stained glass window is one of the ecclesiastic arts that can last through the centuries to inspire faith

By Ronald Bovard

A careful examination of this photo of a restored Tiffany window reveals extensive use of plating.

It is Sunday morning. A young boy stares off into space. Glimmers of deep, mysterious light penetrate his soul through his mind's eye. Ancient images mysteriously form, uplifting his awareness with a sense of past, present and the hereafter. The boy sits in the cold, hard pew on this Sunday morning as light passes through richly colored stained glass painted with the images of men and God's young son. Yet the art is not the glass, it is the light passing through the glass into his eyes, heart and soul.

Many of us have similar recollections of our youthful association with stained glass windows. We need to preserve our stained glass heritage for our children and their children's children. This is the stewardship of the contemporary church.

Preservation of glass windows can be divided into three groups: routine maintenance, repairs and restoration.

Routine maintenance

Maintenance includes cleaning. Special care needs to be taken when cleaning stained glass windows, especially painted stained glass. Ammonia-based cleaners should not be used on stained glass; over time, ammonia produces a negative reaction to lead. Acid-based cleaners--even vinegar--should never be used on painted stained glass since they can damage it. Painted stained glass should always be tested for stability prior to cleaning. When in doubt, do not clean the painted areas of your stained glass windows. The damage to the painted areas of a stained glass window is non-reversible. A professional biodegradable pH neutral cleaner, such as Triton X or Orvis horse shampoo (readily available from your local tack shop), works well and can be safely used to clean your stained glass windows once any glass painting has been tested for stability. The stained glass should be cleaned with a soft cotton cloth.

The perimeter putty that holds many stained glass windows into the sash and steel T-bar system needs to be replaced when it becomes loose. Stained glass window frames need to be painted, the perimeter re-caulked and rotted sections of wood or stone need to be replaced or stabilized with proper epoxy consolidation methods. The steel reinforcing systems in stained glass windows separate from the windows over time due to the expansion and contraction cycles. Periodically, the steel reinforcing bars need to be examined and reattached where they have broken away from the stained glass windows. The steel reinforcing bars do not hold the window up--that is the job of the steel T-bar and mullions and muntins. The steel reinforcing bars hold the stained glass in a flat vertical plane. Since the lead came is very soft, as long as the stained glass remains in a flat vertical plane, it retains its stability.

Damaged or broken areas of stained glass windows need the appropriate repairs for the damage incurred. Broken panes need to be glued back together or replaced. Damaged areas may need to be releaded. Fire damaged stained glass windows need professional evaluation and a complex set of specifications for restoration, or may need to be replaced in part or in full.

Repair and maintenance of stained glass windows can include what some call stop gap measures, which extend the life of your stained glass windows until the time they will need a full restoration. These procedures can be categorized as repairs and maintenance or as restoration, and probably fit somewhere in between.

Measures include re-cementing the stained glass window, replacing the loose or missing glazing cement packed between the flange of the lead came and the stained glass panes. The glazing cement both strengthens and weatherproofs the stained glass window, flattening the bulges and deflected areas of stained glass that have sagged over time--either from structural failure, expansion and contraction cycles or due to a lack of stability in the original design of the stained glass window. Often, the cause is multifold. Some bulging areas will require releading; others can be flattened without releading, depending on the design of the stained glass window and the severity of the bulging.

These and other techniques can extend the life of your stained glass windows for a decade or two before a complete restoration is required. Full restoration involves releading the stained glass window.

One serious problem for historic American stained glass windows is that many were made with lead came that has a short life span of 70 to 100 years. The stained glass windows of the great gothic cathedrals were made with cast lead that contained impurities. Today, we call some of those impurities "alloys." During the industrial revolution, craftsmen learned how to make lead came from pure lead. Pure lead can be milled, forced between sets of rollers into shape with less labor than traditional casting methods. Milled pure lead came has stresses built into it from the day it is made. In many cases, this reduces its life expectancy to about 70 to 100 years. Today, we have lead cames available made with the best alloys and that are extruded (molten lead passed through a die). This gives the came more of the characteristics of cast lead as compared to milled lead came. We can guarantee the inclusion of the best alloys while excluding the impurities. Therefore, a new stained glass window or a releaded stained glass window made with high-quality lead came can be expected to last much longer than the stained glass windows leaded up to a century ago with milled lead. Caution should be used when purchasing a new stained glass window or when restoring your stained glass heritage that only the highest quality lead is used. Milled pure lead, mostly imported from Europe, made the "old-fashioned way," is still readily available and should be avoided.

Restoration

When do your stained glass windows need to be restored? One sure sign is sagging and bulging panels of stained glass. By the time your windows bulge to the point that the stress from the deflection is cracking and breaking out panes of stained glass, you will probably agree your stained glass windows need restoration. Another sign is that your lead came is heavily oxidized, the equivalent of rust on steel. On lead, oxidation appears as a white powder coating your lead came. The oxidation, along with broken and cracked surfaces on the lead came and broken solder joints holding the lead matrix together, also indicate your stained glass windows may need restoration.

The stop gap methods of flattening the bulges, releading the worst sections, recementing, replacing missing steel reinforcing bars, and adding additional reinforcing to weakened areas will buy you time, maybe 15 to 20 years, before you have to restore (relead) your stained glass windows. Eventually, a full restoration will be required. Fifteen to 20 years is considered good for many building repairs. Properly designed and fabricated stained glass windows can have a life expectancy measured in centuries. How many building materials can make that claim?

When restoring your stained glass windows, you will want to correct any structural design defects that have become apparent with the test of time. Some of the most common structural defects are oversized panels. Craftsmen of the past seem to have had a contest to see who could build the largest panel. A large stained glass window is made from many smaller panels of stained glass, preferably about 12 square feet or less in size, divided by the window frames' mullions, muntins and T-bars. Large, oversized panels are prone to failure. A simple correction to this problem is to divide the panel into two or more structurally sound panels. If this process will impact the artistry of historically or artistically significant windows, other techniques can be used. For example, additional reinforcing can be added to the stained glass. Unstable glass paint can be stabilized using modern consolidation techniques. Missing areas of paint can be replaced with reversible cold painting techniques or by painting the missing areas onto a new, thin, clear pane of glass and plating the new pane on top of the original pane to make it appear as originally intended in a non-invasive manner. Small areas of removable (reversible) cold painting can be added to areas such as small pockmarks that tend to appear on otherwise stable areas of kiln-fired glass painting. A surprising number of historic stained glass windows are painted with cold painting (regular oil paints). These surfaces are fragile and need to be treated with great care. All areas of painted glass in stained glass windows need to be carefully evaluated and tested prior to restoration, repair or maintenance. Properly formulated and kiln-fired traditional glass painting should remain stable for centuries. Some older stained glass windows were made from unstable paint formulas or were improperly fired in kilns without temperature controls of pyrometers to carefully control the kilns' temperatures, both of which are required to produce a long-lasting stable painted glass surface.

Ronald Bovard is the principal owner and CEO of Bovard Studio, Inc. Bovard also wrote Windows For The Soul, published by Wardell Publications, and his studio's work has been featured in numerous books, newspapers, magazines and television shows, including three PBS features. Bovard's personal art has been exhibited in galleries and museums around the world. Bovard can be reached at (641) 472-2824 or via e-mail at info@bovardstudios.com. For more information, visit www.bovardstudio.com.