The treatment cycle happens in phases, but first we survey the windows. Once we have a complete survey of the entire building we select in what order we will conserve the windows. With large scale projects, we often don’t take all of the panels out at once; so we organize them into a conservation timeline based on priorities identified in the survey. Once we set the timeline, clients can procure funds tagged to the actions.

Once funding is secured, we begin removing the windows and conserving them according to the treatment proposal.

The internet has augmented the way we communicate with our clients and the general public. With it, we stay in contact with our clients throughout the whole stained glass conservation process.”

The result of our work varies tremendously depending on the project.


This image is from St. Cecelia in San Francisco. The hand was smashed by a soccer ball that came from an adjoining playground. Photos like these enable us to keep on schedule, and on budget, as the client can “sign off” virtually and not physically come to the studio.

Once the conservation treatment is concluded, our team goes back on site and reinstalls the newly conserved windows. Our final goal for each project is to bring public awareness to the sites on which we have worked. This comes in the form of media outreach and this blog. We stay in touch with our clients after the projects are completed, and update them on what we are currently working on in the studio.

SVdP45_18 overall

A majority of the panels we are dismantling in this phase have a high number of breaks. Their condition is not surprising considering they are from the south wall of the church. The south wall is subject to the most extreme weather conditions, which can result in a lot of breaks in the glass. While we were gluing the breaks from Window 45_Panel 18, we discovered that the top of this piece had an original replacement.

Circled above, the image indicates where this piece is located in the panel. Note the thick lead dividing the middle of this piece.”

SVdP45_18_Replacement Piece

While dismantling the panel, we identified a crack just under the large lead and the entire piece was marked as needing to be re-adhered.

Although the bottom two pieces fit back together perfectly, the top piece is a slightly different thickness and upon very close inspection the base glass color and painting do not line up exactly.

We measured the thicknesses of the broken pieces with calipers – the top piece is 7/64″, while the bottom pieces are slightly thinner at 3/32″ (a difference of only 1/64″!). We can therefor assume that the top section was a very good original replacement from when the panel was initially made.”

Key indicators of this being made during the original fabrication are: the mirror image on the other side of the figure does not have a lead line, and the dividing lead had the same patina of age as the rest of the panel.We will adhere the bottom two pieces so they read as one, but will keep the top replacement piece and the bottom half separated by a lead.

To avoid the confusion we initially experienced while looking at this piece, we’ll leave a clue for the next generation of art historians and stained glass conservators. We will use a thinner lead to indicate the piece is a replacement. In addition to the documentation of photographs, reports and rubbings we will present to the church at the end of the project; the smaller lead will act as a visual clue for anyone who may look at this window in 100 years.

Here is an update on the small, devil piece. It is about 20 feet up from the balcony floor and close to 40 from the ground.

At approximately 5″ wide and 6″ high; one could opt to cover the pieces with thick, repair leads and hope no one would notice. But this assumption, applied to the window overall, would literally diminish the artistry of the window.

At Nzilani, we know quality is achieved by the sum of our actions. This piece, along with any other damage to figurative pieces, will get an invisible repair. Our goal is that the casual viewer will only see the original beauty of the window.”

broken devil piece

When the panel was dismantled, we discovered the piece with his hand was cracked in multiple pieces under the rebar.

broken devil piece detail

Currently the pieces are being re-adhered with a two-part epoxy. Then it will be ready for in-painting.


We are well on our way into our newest phase of St. Vincent de Paul. Our current project is restoring three large lancet windows (45-47)  and one large tracery  (48) on the south side of the church.

This small devil is in the studio as part of the current treatment campaign. We have yet to dismantle this panel and see what condition it’s in. In the meantime, we’ve been intrigued with the details found in the paintwork. Note his extremely long finger nails and one outstanding toenail, along with the luminous green color of his skin and vibrant orange cloak. More updates on this panel to come in the next few weeks.

view of the south side of the church

The beginning of 2015 started off with a large project at the south side of St Vincent de Paul. It’s really exciting because this is the “window” we had originally been contacted to assess 4 years ago when members of the church noticed water damage along the sill. Since the damage was happening intermittently and at a slow pace; we decided with the church to start with smaller windows to familiarize ourselves with conditions specific to the building’s architecture and to streamline our treatment process.

This approach paid off tenfold. As you can read in previous posts, Nzilani now has intimate knowledge of key components of the Century Studios production process, and how the windows interface with the rest of the building.

As a result of our past work, we were able to stream-line the removal of the “Christ the King” panels (69 in total). The treatment process is also going faster – without compromising the integrity of the work.”

Typically, south facing windows deteriorate faster (and with worse damage) than windows facing other directions. These windows fit this criteria. Compared to the other windows; the lead cames were more oxidized and weaker, there was more putty loss (and as a result panel bowing), and the wooden frames around the panels were damaged by constant exposure to the sun and water damage.

The windows are also directly over the main entrance to the church and “float” above the choir balcony, which is used weekly by the voice choir, organist and bell choir.

Part of our treatment scope is ensuring our on-site work is as minimally invasive to our clients as possible.”

This is a perfect example of how we worked with the church to accommodate their needs. The outside was covered with “shrink wrap” to avoid dust and debris falling onto parishioners who enter the church multiple times every day for worship.

Equal care was taken on the inside, where we covered the scaffolding with clear plastic and protected corners of detailed woodwork holding the organ pipes with ethafoam. Of particular interest was maintaining access to the organ console for use, while protecting it while we worked. We created a sealed alcove that enabled organists to safely play while staying clean and unencumbered by our labor. We were rewarded with unofficial performances as they practiced – one of the lesser known perks of working in religious spaces.

view from inside the church, near the organ

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Last year, Nzilani was approached by the Swedenborgian Church in San Francisco to work on a stained glass window of St. Christopher by Bruce this Porter. Our discoveries of Porter’s work proved fascinating and challenging with the condition of the window. Church parishioner and photographer Doug Stinson worked closely with us to document our conservation process of St. Christopher. It is currently featured the website, “Art Matters: Online Art Magazine from Thomas Reynolds Gallery.” In addition to this online publication, Doug also curated a book on the whole process.

Here’s the link to learn more!

*photos by Douglas G. Stinson

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At Nzilani, we’ve developed a protocol for windows in architectural settings in which surveys are imperative before embarking on any conservation. Multi-phase treatments are considered components of a whole, rather than conceived and executed in isolation (or worse, as an afterthought); even if separated by years.

Viewing the project holistically is key to its sustainability.”

The survey encompasses three main topics: Condition, the (possible) need for Protective Glazing and the proposed Treatment Cycle.

Within the condition section we:

1. Evaluate the condition of all stained glass windows including the supporting framework -its stability is integral to the window’s longevity. An unstable frame will directly affect the long-term outcome of a newly conserved window.


Sequencing is key when considering when and which part of the building should receive care first.”

  • Is the frame in good condition? Does it need to be repaired in conjunction with the window?
  • Orientation in the building can affect the condition of a window. In general, south facing windows deteriorate faster than other windows due to direct sunlight, but other factors such as roof overhangs, the weather and landscaping can also affect their condition.

2. Importance to the client due to use, symbolic representation or value must also be considered.


This image is from St Boniface Church. The window is relatively stable, and in an alcove off the sanctuary. But, the image is OF St. Boniface, with a badly painted replacement head from a previous treatment campaign. The significance of the piece makes it Priority ONE, rather than 2 or 3.

Next, we consider the option of protective glazing, also known as secondary glazing. Simply, it is a second material installed to the exterior of the building to add a layer of protection for the art glass. Installed correctly, it can prolong the life of the window; but improperly designed and installed it can accelerate the rate of deterioration.

For every project we ask “Is exterior protection necessary?”

Here are a few considerations when looking at a potential project…

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Only after answering all of these questions, do we propose a treatment of the windows. Next week we’ll discuss the treatment cycle.

Broadly placed in two categories: museum objects, or functioning components of historic buildings; the criteria of conserving these works of art are project-specific. The majority of our projects at Nzilani take place in historic buildings. Our first priority for the windows is to stabilize them in order to survive and be appreciated by future generations. But beyond that baseline, the necessities of the two are divergent.

Our final goal for each project is to bring public awareness to the sites on which we have worked. The more advocates we have for conservation of art, the better.”

Stained glass in an architectural setting must function as a window. As such, it inherently experiences exposure to the public and weathering, which means it will require treatment in the future.

When working in the field, we must consider the window as a key component within the building in which it is situated.

But in that environment, what is the definition of a window? Where does the scope of our work stop?


The wooden or metal border stops or putty?


The framework?


Or, the entire wall including surrounding overhangs and roof?

Each project requires different parameters. Identifying what falls under the stained glass conservator’s purview is paramount to a successful treatment and satisfied client.


Here is how one perceives a “typical” leaded window to look. Yet this is only the base layer of a Tiffany panel we have in the studio.


We had to remove over 99% of the platting from panels 2 &3 from Tiffany’s “Garden Staircase” in order to clean and stabilize all of the different elements underneath. When laid out, the loose platting made up an image all on its own.


Removing the platting before conservation.


Just the platting.


Reconstructing the platting after conservation.


These pieces add depth of color and tone to the overall window and are different than other platting we have dealt with before. The platting is two, sometimes three layers thick. Some is soldered and some is leaded together.  In order to solder them to the base level of the panel; we must copper foil the pieces of platting together. The platting also significantly varies in size. Some pieces are as small as one inch by one inch, while others are over two feet long. The top layer is a translucent purple color with minimal texture. The second layer is etched flashed blue on clear glass that “reads” as clear to yellow to green and finally blue – often in one piece.


To treat a section, the platting must be removed. This means that all of the lead and copper foil surrounding the border of the glass first must be removed. Then all of the pieces are cleaned thoroughly. As we clean, we note other damage that we will treat afterwards.

Removing the top layer of platting exposes the middle layer of the panel. We can then fix cracks in the glass or lead, which we can’t otherwise access.”

We also replaced all the areas of putty loss with new putty – patching holes to improve the panel’s stability. On the image below, the orange marks denote all of the cracks we discovered on the panel after the platting was removed. Some of the cracks go through to the other side and some are surface cracks. We glued the surface cracks and taped the other cracks so we could glue them when we worked on the other side of the panel.

The bottom, right side of the panel was the weakest part. When the panel was removed for conservation, most of that section separated and the pieces formed the staircase were bowing. The border lead had to be completely removed from that side so that we could flatten out the pieces and securely add the platting.


In order to maintain the integrity of the panel, we tried to keep as much of the original lead on the staircase area that we could salvage. We matched the old lead type in areas we had to replace with the same profile lead and cleaned the old lead in order to solder it to the new border. Once everything is puttied we will polish the lead in order to buff it back to it’s originally intended darker color.

On any stained glass conservation project, we are are constantly weighing the validity of conserving a piece against the necessity of making it function as a key component in a building’s architecture.

One of these decisions includes deciding when to keep the original border lead and when to replace it. The window we are currently working on is proving to be in worse condition than we initially anticipated when viewing it in situ. Multiple parts of the panel were discovered to be unstable when it was deinstalled. The border leads are in the worse condition because they interfaced with the framework and they are encapsulating extremely heavy panels. Many areas of lead are cracked and weak. In some areas we’ve had to replace the border lead entirely.

Our biggest challenge while conserving these Tiffany windows has been finding the balance between restoring the windows and keeping as much of the original material as possible.”



When possible, we are soldering new border lead to the original lead – only replacing sections that are weak or damaged. In order to create a clean join between the new and old lead, we must abrade the edge of the old lead, otherwise the solder will not cleanly bond. In the image below, we replaced the border lead on the left side of the panel in order to stabilize the area that had to support a lot of platting. The right section was stable enough that we could preserve it.


The position of the lead, and the type of glass it abuts to also are considered. For example, we will take more time to preserve a side border or top than a bottom border because they do not hold as much weight.

Bottom borders in general have been compromised by over 100 years of panel weight. It took 4 people to lift each section during removal from the building – twice the normal amount! Weighing the panels wouldn’t have been safe, but we suspect they are around 150lbs each. When you consider that in addition to the direct weight of the glass and lead on the border, there are also the platted pieces cantilevered off either side, you can imagine the damage that can occur.

That said, each area is its own, unique case. Here you can see that the original flashed glass piece with the Tiffany label is still connected to the original border lead, even though it is at the bottom of the panel. For the purpose of conservation (and maintaining the value of the window), it is important to leave the Tiffany Studios signature as intact as possible. Luckily this area of the window is relatively structurally sound. Therefore, we maintained the original border lead in this section.