Restoring An Original Tiffany Window

The restoration of any historic window is a great responsibility for both the window’s trustee and the contractor. The owner or trustee of the stained glass window must ensure that the restoration company has the training and experience to undertake all necessary work in a professional manner. References should be provided (and checked) and an extensive plan of action must be submitted by the contractor outlining the full extent of restoration, including adherence to historic conservation procedures. Comprehensive insurance must be engaged to safeguard against any perils that could occur to the window during removal, rebuilding and re-installation or at the very least the building’s current insurance coverage needs to be extended for off premises work.

When prestigious works by distinguished artists such as a L.C. Tiffany, J. LaFarge, F.L. Wright or others needs to be restored, it may be advisable to engage the services of a professional conservation consultant, specializing in stained glass restoration. It is advisable to locate a consultant that is a member of a licensed architectural firm. They will advise the trustee on the extent of work necessary and inform them on specific technical requirements to ensure that irreversible restoration methods are not undertaken. Historic restoration is definitely a job that is worth doing right and should be entrusted only to those who have proven to be trustworthy.

The first step in restoring any historic stained glass window is to document its current physical state and appearance. It is of the utmost importance to photograph the stained glass window in both transmitted and reflected light prior to removing it from its frame.

Take several photos of the window with transmitted light, (natural light passing through the stained glass) without flash and being careful that the interior lighting is extinguished. Since the exposure time will be longer (due to lower available light) it is advisable to mount the camera on a tripod when taking photographs from the interior side of the stained glass window.

Next make a record of the interior and exterior surfaces of the stained glass window in reflected light (lighted from the same side as the camera). The sun’s light will usually suffice for the exterior photos but a supplemental flash may be needed for the interior surface photographs. Separate photos should be taken for each stained glass panel (section) of the window, plus detailed photos of specific areas with extensive damage such as cracked glass, missing areas of glass, badly damaged paint, etc. Additional photographic documentation may be made back at the studio if required.

Prepare the windows for removal by securing loose and/or broken pieces of glass with conservators tape. It is always advisable to secure the entire width and length of the panel with tape, especially if the window’s structure is weak and fragile. It is important to check any painted areas for stability prior to placing conservators tape on these surfaces. If the glass paint is unstable or the stability of the paint is in doubt, the painted side of the stained glass must not be taped. Once the panels have been secured, they are carefully removed from the window frame and placed into wooden packing crates with foam rubber sheeting to separate and protect the fragile panels during transport. We pickup and deliver the panels in our own trucks.

Once back at the shop, the extracted stained glass windows are prepared for restoration. The first panel is placed onto the glazing bench where more notes are taken and more photographs made (if necessary). Then a rubbing is made for each section of the window by placing vellum paper over the window and rubbing colored oil pastels (or artists charcoal) over the lead lines to create a full size pattern of the lead matrix. This pattern will be used later for reassembly. If the section contains plating, as the Tiffany window in the illustration does, a separate rubbing is made for each layer of plate. These additional plate rubbings are done on top of the first rubbing using a different colored pastel for each successive layer of plating (a rubbing is made after each plate layer is removed). This will show the fabricator how each plate is "registered" on the window during reassembly. Notes are taken of the size, profile and description of each lead came or copper foil area within the stained glass window and this is recorded directly on the rubbing. Then two copies of each rubbing are made one for reference and one as a working copy.

The restoration specialist must be sure that sufficient records have been made to ensure an exact reconstruction can be achieved. Only then are the stained glass panels carefully disassembled. The lead came is cut away and one glass piece at a time is removed and placed in it’s correct location on the working copy of the rubbing. During disassembly it is important to keep a sample of each different lead came size and profile or a section of the copperfoil assembly for reference and documentation.

When the entire panel has been disassembled it must be cleaned and inspected. Each piece of non-painted glass is cleaned with Triton X-100, a professional quality, non-ionic detergent (made by City Chemical Company of NY) or an equivalent pH neutral glass cleaner mixed with distilled water. Prior to cleaning, painted areas of the window must be tested to determine that the paint is stable. If it is, these areas should be gently cleaned with a soft cotton cloth and distilled water. Unstable painted areas need be stabilized. The basic treatment is to coat the painted surface with a restoration grade clear fixative to bond the remaining paint to the glass. However, it is intensely important that the fixative used be chemically compatible with the underlying paint to ensure no further damage is induced. For this reason it is necessary to consult an expert restoration specialist to determine the appropriate consolidation method for the particular problem encountered. Areas where the paint is badly faded, has been washed away, or otherwise lost, should be restored by first treating the existing paint with the clear fixative. Then the missing details are painted onto a new piece of 1/16" (1.5 mm) or thinner clear glass that is plated over the original painted stained glass. This ensures the historic work remains unaltered and undisturbed and makes the restoration fully reversible in the future.

Cracked and broken pieces of stained glass are repaired by edge gluing with clear Hxtel™ epoxy (a commercial brand product), clear silicone, or by copper foiling and soldering the pieces together. The specific repair method will be decided based upon what is best for the historic preservation of the particular stained glass window.

Missing pieces of art glass can sometimes be closely matched from the more than 4,000 colors, densities and textures that are manufactured and available today. If a close match cannot be found from available glass, you can plate two layers of stained glass together to produce a third color and texture. If necessary several plates can be combined to give the stained glass restoration artist countless possibilities. In some cases where a glass making formula is known, a glass manufacturer may be willing to custom create a particular stained glass sheet to match a destroyed original piece. This is an expensive alternative but if the missing glass is dominant in the design or if the window is an exceptional work, this may be the best solution.

The various sizes and profiles of lead came also need to be closely matched. Many of the came profiles are available as standard stock items manufactured from existing dies, however other more specialized shapes may need to be specially ordered from custom or rarely used dies and depending on the importance of the window, may be a necessary step. Other cames are hand made for a perfect match.

Once all the glass has been cleaned, broken pieces repaired, missing pieces replaced, painted pieces replicated, and all other materials are obtained, the stained glass window is ready to be reassembled. The pieces will be placed on the working copy of the rubbing, precisely as the window was originally created. The fabrication will be carried out by skilled craftsmen in essentially the same tried and true method as the window was fabricated decades before.

The Tiffany window we are restoring here has complex plated sections that will require the fabricator to devise an assembly of lead cames to create a shape otherwise not available. They will solder several strips and/or layers of came together to create a shape based on the sample saved during disassembly. We have found that a modern improvement can be made to the original structure of plated sections by applying a silicone seal around the edges of the stacked plates of glass. This will prevent dirt and water from collecting between the plates, which cannot be cleaned without disassembling the window. Contamination of plated sections is a major problem encountered in historic windows that include extensive plating.

Any structural deficiencies in the original windows should be addressed to prevent the premature failure of the window in the future. One major structural remedy is to use lead came that has sufficient tensile strength. It is crucial to use a lead came manufactured by the extrusion process using a lead alloy that contains antimony, silver, copper, or tin. The original stained glass window was probably fabricated using pure milled lead (without alloy additives) which is comparatively soft and malleable (lead alloy came is a recent development). This improvement alone will greatly increase the expected longevity of the stained glass restoration. Another common structural deficiency is the use of a single layer of relatively thin glass, usually 1/8” (3 mm), in the borders. This fragile border is required to support the heavy weight of the central glass section and is particularly troublesome in windows with multiple plates of glass which add considerable weight. Unfortunately, this situation often results in the folding and sometimes total collapse of the border, especially at the base and lower sides of the window. A simple, reversible, non-invasive remedy for this deficiency is to apply a second plate of clear glass to the border areas on the exterior side of the window, thereby doubling the strength of the borders.

When fabrication is complete, the window must be cemented with a glazing cement specifically formulated for leaded windows. The cementing process packs the space between the flanges of the lead came and the stained glass with a sealant to stiffen and strengthen the window as well as weatherproof it. Most cement compounds have a black dye component to enhance the surface the new "silvery colored" lead with a dark, richly colored patina to give it a more mature appearance.

During a restoration such as this Tiffany window, we take special notice of areas with the most structural damage. These areas of distress may be due to an insufficient supporting structure or to weaknesses within the windows design.Whatever the reason it is our responsibility to correct the problem in the least intrusive way. Obviously these areas require additional structural engineering and one of the most effective solutions is to attach brass rebar directly to the lead in the structurally deficient areas of the window. This rebar is a flat brass rod, 1/16" (1.5 mm) thick and anywhere from 1/4" to 1" (6.3 to 25.4 mm) wide. It is soldered directly to the lead came, perpendicular (90°) to the face, on the exterior side of the window. Preferably these rebars should be kept as straight as possible but they may be bent to follow along the length of a gently curving lead line. This technique structurally reinforces the stained glass window with minimum aesthetic impact. (see example on this page).

While the stained glass window is "in the shop" undergoing restoration, it’s an opportune time to take up the necessary repairs and restoration to the window’s frame. In some extreme cases the frame may need to be totally replaced, at the very least it should be cleaned, sealed and refinished. If the window restoration company does not provide these services, a qualified carpenter should be called to make an assessment of the frame’s integrity and complete the repairs.

The culmination of any restoration is the time of reinstallation, when the restored window is returned to its rightful home. A scrupulously restored window, with structural weaknesses remedied and installed with a properly vented protective covering (see this page), can be expected to last significantly longer than the original stained glass window, before it will require another restoration.

It is a very gratifying experience to return a Tiffany or other historic stained glass window to its original appearance and condition. It is rewarding to witness the dramatic contrast between the dirty, deteriorated, misshapen window of the past to the richness of color and structural integrity of the restored installation. It is a thrill to return the many lost details of a window, details that seemed to be hidden in the past and are now mysteriously resurrected into the living present.