Tips For Conservators When Completing Stained Glass Restoration Projects

1.3 New Mexico Military Institute Roswell NM Faceted Glass Restoration 1 1

Stained glass is an integral part of a historic building’s architecture. While restoration projects are often limited to the interior, it is important to assess the main structural components of the building including: foundation, walls, doors, windows and roofs. In many cases, restoration of the exterior façade, restoration may be required before other work is done. If this is the case, it is important to document the process as thoroughly as possible. While some signs of age are normal and even desirable, more extensive treatment is necessary for more severe damage. The following are some tips for conservators when performing a restoration project.

Before beginning any stained glass restoration project, a thorough evaluation is necessary. Stained glass repair requires careful assessment of the damage. In addition to evaluating the damage, a conservator should examine the entire window to determine if it is structurally sound or needs repair. The process will require a thorough evaluation of the stained glass to ensure the most cost-effective restoration. To determine the most appropriate course of action, a consultant should evaluate the stained glass and advise how best to proceed.

The research phase of the restoration project should include an in-depth condition report. The team should also record previous interventions or repairs to ensure that the work is appropriate for the piece. During the research phase, a conservator should ask questions about the original craftsmanship of the stained glass, which may take some time. This will allow them to understand the original intent of the artist and the state of the piece. If possible, a conservator should assess the extent of the damage.

Once the damage assessment is complete, the next step is the restoration process. A professional will assess the stained glass and provide a detailed quote. A thorough estimate of the damage will be necessary, and the stained glass should be carefully examined and repaired if necessary. After restoration, a conservator will carefully examine the stained glass to ensure that all components are intact. When the stained glass restoration process is completed, it is usually more cost-effective than replacing the stained glass entirely.

Once the damage assessment is complete, the restoration contractor should discuss the costs involved. If the window is damaged, a restorer should provide a quote for the entire project. These fees may be paid for the cleaning and restoration of the stained glass. A conservator should be able to answer these questions, if necessary.

Inspecting stained glass is essential. A technician will accurately assess the damage and determine the most appropriate solution. Stained glass is incredibly fragile and requires special care. A restoration process should be as thorough as possible and be accompanied by a thorough inspection. Stained-glass experts will inspect the windows to determine the type and extent of damage and recommend solutions. It’s important to choose a restorer who has the experience to do a good job.

The scope of a stained glass restoration project can vary widely. The more in depth stained glass restoration methods will be more labor intensive, and thus more costly. Most often, the stained glass restoration scope of work can be presented in multiple levels of in depth repair, each with different lengths of time that the restoration will last. See below some of the different scopes of work that pertain to different mediums of stained glass. For each of the mediums, we will explore some signs that the stained glass is in need of restoration.

Leaded Glass Windows:

There are many warning signs that indicate that leaded glass windows are in need of restoration and repair.

  • One of the most common would be leaking windows. There are several options to help combat leaking windows with varying degrees of labor, material, and cost requirements.
  •  Daylight showing through the glass. Sometimes as windows age due to settling of the building, exterior weather forces, vandals, and many other contributing factors, stained glass windows can sometimes develop voids in the art glass window where daylight pokes through. This can be a good sign that the stained glass windows need some attention.
  • Bowing leaded glass. Another sure sign of the need for leaded glass window repair is when bowing or bulging stained glass begins to appear. This is also due to building shifts, exterior weather, improper care of the stained glass, and improper reinforcing of the stained glass windows.
  • Cracked stained glass is a sure sign of exterior weather conditions, building settling, and even vandalism. Art glass repair is the most common stained glass repair that is completed.


If the leaded glass windows have been taken care of over the years and maintained properly, a simple and most common stained glass restoration scope of work would include scraping old, loose, flaking stained glass putty and applying new stained glass putty. Applying stained glass putty is critical to keeping a stained glass window structurally secure and maintaining the structural integrity of the stained glass window. This scope of work can be completed in place without needing to remove the window and can help to fill any voids where daylight may be poking through and help to seal up any voids where water can make its way through the stained glass window.

Another common scope of work includes installing new reinforcing bars to stabilize the leaded glass windows. If you notice that your stained glass windows are developing bulges and are bowing, this is likely due to improper reinforcing when they were first fabricated. It’s an industry best practice to install reinforcing bars along critical lead lines to reduce the chance of bowing stained glass. Fortunately, it is possible to install stained glass reinforcement bars while the windows are in place to reduce any bulges and to increase the lifetime of your stained glass windows.

Cracked art glass panes can be replaced without need to remove the window. It’s important to find a well matched glass to allow the repair to blend with the existing glass as much as possible. It’s important to find a stained glass restoration studio with a large stock of both antique art glass and new art glass to give your stained glass restoration the best possible appearance. If a glass is not severely cracked, it is possible to stabilize the cracked stained glass using a clear silicone sealant. This would be the process of applying a small bead of clear silicone over the crack to prevent it from shaking loose. Another possibility would be to install lead straps over the cracked glass. This process would include using a similar profile lead caming and install it over the cracked glass to give it the appearance as another lead line. This helps the crack to blend with the rest of the window while also stabilizing the glass. The main benefit of this method is that it doesn’t require matching glass which will reduce the change of replacing the damaged glass with mismatched glass, but also reduce the labor cost required to complete the repair therefore providing a nice cost savings.

The most in depth stained glass restoration scope of work would include removing the window to re-lead it. The process of re-leading is the most labor intensive scope of work and is only recommended when the windows are too far beyond repair. It’s important to choose a reputable stained glass restoration studio that has good ethics and that has interest aligned with the best interest of the stained glass owners. While it may be easier to keep the stained glass studio’s craftsman busy with more work by recommending the most costly and labor intensive service, it’s not always necessary especially when it would be best to do an in place restoration. The process of re-leading a window includes creating a layout of the damaged windows, numbering the pieces identically on both the layout and the stained glass window, separating the pieces from the old lead, and fabricating the window using new lead and proper reinforcing. It’s important to choose a studio with the capacity to replace damaged or cracked stained glass pieces with closely matching stained glass. When working with a studio with a large selection of antique glass inventory, the stained glass owner can rest assured that their stained glass will be like new without any eye-sore patching. It’s also critical to find out if the stained glass restoration studio being used has the ability to paint and fire new stained glass pieces in the event that any of the painted glass pieces were severely damaged.

Faceted Glass Windows:

The most critical warning sings to note when assessing the condition of a faceted glass window is if they are leaking and if there is daylight protruding between the glass pieces. Faceted glass windows are made using epoxy & slab glass. These window types are similar to concrete slabs, in that once they are poured, they cannot flex or else they will crack. Flexing can occur from many different factors include building settling, exterior weather conditions, and even vandalism impacts.

If you notice that your windows are leaking or you can see daylight between the glass, or even cracking within the epoxy areas, then it’s a sure sign that your windows are in need of faceted glass restoration. Often the issue occurs when the windows are fabricated. If the original craftsman were not highly skilled or working in a temperature controlled facility, it’s possible that a few things occurred during the window fabrication.

  • The first possible point of failure is the miss pouring of the epoxy to the proper depth, causing the panels to be too thin and therefore very weak compared to the industry best practice of 5/8” to 3/4”.
  • It’s possible that the faceted glass windows were not poured in a temperature controlled facility to allow for the careful curing of the epoxy.
  • It is also possible, and most common, that the windows were designed too large, and the windows couldn’t be structurally secure to support the weight of themselves.


The process to restore faceted glass windows is limited to two different methods:

  • Single glass replacements. This method is normally not recommended unless the budget of the customer simply doesn’t allow for a full recast. The single glass replacement scope of work includes matching up the glass, cutting it precisely to fit in place of the damaged glass, and replacing using some sort of high strength adhesive or epoxy to secure the new glass piece. This method is not normally recommended because the window could pose as a safety hazard if it does have concealed damaged within the epoxy and runs the risk of crumbling in place.
  • Full recast. This method is most recommended because if the faceted glass window withstood an impact that caused any sort of damage, it’s likely that there is concealed damage within the epoxy that may not be immediately apparent. This is the most labor intensive method but generates the best and most long lasting results. This scope of work includes creating a layout of the existing window, numbering the pieces identically, separating the old epoxy from the glass, and pouring a new window using the original glass.

Mosaic Murals:

There are some apparent signs that indicate that a mosaic mural is in need of restoration.

  • Cracking between the glass pieces. This occurs normally from structural settling or improper installation. It’s important to assess the structural conditions of the wall.
  • Pieces falling out. This normally occurs from both settling of the building, improper installation, but also improper maintenance of the mosaic mural. It’s important to do some important maintenance especially if the mosaic mural is exposed to exterior weather elements.


The most common scope of work to restore a mosaic mural includes replacement of fallen pieces using as closely matching mosaics as possible. When choosing a mosaic restoration contractor, it is important to determine if this studio has a large in stock inventory of the mosaic mural in both color and type to ensure replacement pieces are going to blend nicely within the original mosaic. Once the replacement of the pieces is completed, it’s important to regrout the entire mosaic mural. This will fill any voids that water may enter into the mosaic and cause any freeze/thaw cycle splits. Another important step is to apply a water proof sealing compound to the mosaic to prevent moisture penetration.

When restoring stained glass, it is essential to follow the same ethical guidelines as other types of conservation. A good conservator will follow the rules of modern conservation & industry best practices. The goal of the restoration is to restore the stained glass as much as possible. It will not only preserve its historical value but will also make it more attractive to the public. The stained-glass repairs will also preserve the architectural fabric of the building and provide a beautiful viewing experience for generations to come. Cavallini Studios is a professional & highly skilled stained glass restoration studio with the capabilities to make your stained glass back to like-new condition.

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