Stained Glass Windows: Restoration and Care

“THE WINDOWS at Temple Mishkon Tephilo are fine examples of mid-century American stained glass. Their simple repeating pattern with minimal paint allowed for all of the windows to be commissioned at one time at a reasonable cost. This also provided the proper visual element for the worship space while diffusing, but not obscuring, the strong Southern California sunlight.”

So wrote David Judson, the head of America’s oldest family-run stained glass studio: Judson Studios in Highland Park. He is a great-great-grandson of its founder. A little more than 19 years ago (2-13-03), Judson assessed the condition of our art glass windows—which are now 74 years old—and offered guidance for their restoration. 

 

This post restates that report, as re-edited with a focus on its action items. Although we don’t yet have cost estimates for the needed restoration work, at least we have reliable guidance as to what should be done. [I also add my own observations, in square brackets.]

[INTRODUCTION: Of our 14 stained glass windows, 12 are exposed to the elements, while 2 are protected by the adjoining school/office building that was constructed later. The exposed windows, when viewed from eye level in the sanctuary, appear to be in fairly decent condition. It’s only when I get up on a ladder and look closely that numerous problems become obvious.

Rusty frames, bowed windows, cracked glass, and unsightly protective wire glass

Unfortunately, no remedial action appears to have been taken during the 19 years since Judson’s assessment, which is restated below. And of course deterioration has continued in the meantime.]

The Six Windows on the South Side: Major Recommendation

In 2003, these windows were deemed to need immediate attention. 

1. As the highest priority, re-lead the windows with matching came. [Came is the formal name for slender grooved rods made of lead mixed with tin. It comprises the matrix that holds together the panes of stained glass.]

REASON: The sun-baked exposure of the south-facing windows has caused some deflection and cracking of the came matrix. Furthermore, protective outer glazing was improperly installed on most of these windows, which has presumably accelerated the matrix’s deterioration (see next item). The matrix’s failure is shown by the marked deflection near the bottom of the few windows that are not covered with protective glazing, such as in the photo above.

All Twelve Exposed Windows: Major Recommendations

2.  Replace the waterproofing compound (also referred to as cement or putty). Carefully remove any loose compound underneath the leads. Re-cement the windows with a mix of whiting (calcium carbonate) and organic oil medium. (A lamp black dye can be used to repatina the surface of the leads.)

REASON: Over time, the waterproofing compound has naturally dried out, crumbled, and fallen out of the crevices between the art glass and its matrix. The process of re-rubbing it into the crevices not only waterproofs the leaded panels, but also adds to their rigidity and strength.

3.  As the windows are removed for releading and recementing, replace the existing internal support bars. Also weld and solder additional support bars, as follows. Install two vertical bars on all of the upper sections (which is currently the case in only some windows). In the lower (casement) sections, install another horizontal bar across the bottom edge of the lower blue border. (Use 1/8" x 3/8" bars of cold-rolled steel and galvanized. The bars should taper with a 30-degree angle on each end. Extend the outermost part of the perimeter lead, so they are tucked under the frame. Solder each bar to every lead joint that it crosses.)

REASON: These unobtrusive bars redistribute the weight of the windows to the frame—taking the load away from the stained glass, in which it induces deflection.

4. When the leaded-glass panels are removed for restoration, clean the frames of all putty compound, loose rust, and paint. Repaint them with a rust-protective paint.

REASON: Most of the frames have noticeable rust damage and may be in danger of weakening and losing their strength. [None of the 12 exposed windows can easily be closed (i.e., shut tight). Three (all in the mezzanine) can be closed only with difficulty. The remainder leave a vertical gap of ¼–½ inch, due largely to rusting (roughening) of the frame’s sealing surface. Meanwhile, over time, the metal latches have become brittle and broken off upon being overstressed by trying to force closed a window that is too damaged to shut properly. Most latches are missing.]

 

5. Reinstall the protective outer glazing (currently clear plexiglass or wire glass), so as to allow proper air circulation between the layers. Replace the wire glass with plexiglass or equivalent.

REASON: Currently the outer glazing is not only too close to the leaded panels but also entirely sealed with putty. This arrangement creates a solar oven between the two layers of glazing. The extra trapped heat then degrades the stained glass matrix. As for wire glass, it creates a poor visual experience with the pleasing simple design of the windows. And some of the wire glass is cracked, making the leaded glass appear as though it is cracked. [Judson actually recommended permanently removing the protective outer glazing from all of the windows. That’s because he perceived the threat level to be too low to warrant keeping such glazing. Unfortunately, however, times have changed since 2003; a synagogue’s security needs are now considerably higher. Fortunately, it seems possible to have protective glazing that neither degrades the leaded glass nor is an eyesore.]

 

6.  Replace the exterior setting putty, which is missing from many of the frames.

REASON: Over time, this putty compound has naturally dried out, crumbled, and fallen off. In addition to some metal clips, it is what holds the window panels within their metal frame. Already by 2003 it was failing on all of the windows. [In short, our windows are no longer securely held within their frames. They should be treated as fragile.]

7.  Glue the edges of the cracked pieces of glass with Dow Corning RTV #732 or 734 silicone, or a similar approved material. If the break is not clean and light reflects on the cracked edges, a small lead can be used to repair the break. No glass should be grazed or trimmed. As for missing pieces of glass, replace it with as close a replacement that can be found. (It will be difficult to find an exact match, so once a replacement is decided upon, extra glass should be purchased and kept for any future repairs, to maintain consistency.) And if the missing glass was painted, replace it with a hand-painted matching piece. (All replacement painted pieces should be signed and dated by the studio and artist, on the edge—where it will be hidden by the profile of the lead came.) [Perhaps original pieces can be taken from the 2 windows that abut the school/office building, and replaced with new ones—because in those windows it won’t be obvious if the replacements don’t match exactly.]

REASON: These measures follow standard architectural preservation practice.

 

8.  Reinstall the casement crank system and the missing latching handles, as needed. Do not use a pole to open and close the windows. (Conversely, as the hinges are treated for improved operability, make sure that the windows cannot then be damaged by being banged shut by the wind, or by pulling them closed carelessly.)

REASON: It appears that the glass in several windows has been damaged (cracked) by someone trying to prod them with a pole. [It takes less than 10 minutes to open or close all windows by hand, with the help of an 8-foot ladder.] 

 

FURTHER NOTES

Lead Matrix

The lead matrix on the remaining stained glass windows (in addition to the six south-facing ones) may well be need to be replaced by the time those windows turn 80 years old, in 2028. Although it is normal have this work done every 80 to 150 years, a relatively shorter life span is expected for the temple’s windows, due to the salty air along the coast. Furthermore, the proportion of lead in the came matrix is likely to have been substandard, given the postwar shortage of lead at the time of the windows’ fabrication. [I infer that this factor would shorten the useful life as well.]

Metal Sash

The metal sash is beginning to show age and they appear to be weakening. [It’s not clear to me what Judson’s statement here refers to, or what measures should be taken in response. It may well refer to the metal frame that is set inside the wall opening, as opposed to the frame of the casement windows themselves.] 

Regular Maintenance

The frames appear to rust quickly, due to their proximity to the salty ocean air. To prevent rust from taking hold, the restored windows will need regular maintenance that arrests rust as it develops on the frames. [The windows should also be shut tightly whenever possible.]

 

Source:  “Condition Report and Restoration Guidelines for the Stained Glass Windows,” in Historic Structure Report, prepared by Historic Resources Group, July 2003. (Thanks are due to Sue Kaplan for having arranged for that report.)