How to Maintain Stained Glass Windows


Stained glass windows have been an important feature of churches for hundreds of years, from the Middle Ages onwards. Styles and methods may have changed over the years, but they are still used heavily today. Contrary to what many think, stained glass windows tend not to be any more fragile than regular windows. That said, some of these works are hundreds of years old and, as with all glasswork, are prone to receiving damage over time. Read on to discover more about the historical and religious significance of stained glass windows and how to maintain them to avoid irreparable damage.

Stained glass windows at Canterbury Cathedral

Canterbury Cathedral is one of the finest ecclesiastical buildings and home to some of the world’s oldest stained glass. Established in 597CE, the cathedral is infamous as the site of the murder of Archbishop Thomas Becket in 1170CE, who was later canonised as a saint by Pope Alexander III in 1173CE.

Shortly after the Martyrdom of Becket, further trauma struck the cathedral as it suffered damaged from a fire in 1174CE. However, the monastic community took this as an opportunity to significantly extend the east end, as by this point, there was an influx of pilgrims flocking to Becket’s shrine.

During the medieval period, literacy rates were low. Only a select few of the English population would have been able to read Middle English, and even less would be able to understand the language of the Catholic Church, Latin. Therefore, the purpose of stained glass at Canterbury Cathedral was not just to visually tell stories of the Bible, but of saintly Becket’s miracles. These “miracle windows” had the effect of prompting the pilgrims to pay tithes to the cathedral.

Conserving stained glass windows

Whilst Canterbury Cathedral has some of the most notable examples of stained glass windows, you may also be a custodian of other historic ecclesiastical glassworks. If so, you are likely to want to keep them looking in the best shape possible and avoid them sustaining any unnecessary damage through regular maintenance and inspections.

Signs of damaged stained glass windows

During your regular inspections, there are many simple signs to look out for that can indicate that windows should receive a full inspection by your inspecting architect. The first is looking at the structure of the window. Is any glass loose, is it bulging anywhere, is the leadwork all holding together properly? You should also check for cracks and powdery deposits on the lead itself, as this could be an early sign of damage that is better to rectify sooner rather than later.

The next thing to check is the structure around the windows. If there is rust on the iron frame, water stains, moss or algae, or even crumbing walls, there is an issue with the weatherproofing. Likewise, if you see algae on the glass itself, or if the paintwork becomes discoloured, faded or flaky, this could also be a sign of poor weatherproofing.

What causes damage to stained glass windows?

One of the leading causes for damage is purely the age of the work itself. The lifespan of leadwork tends to be around 70-100 years, so if you aren’t sure how long ago your stained glass was serviced, it could be a good idea to get it checked over. Left in an unchecked and damaged state, the leadwork could buckle and the whole window could collapse.

You could also have inadequate support from the surrounding structure, such as the ironwork or walls, especially if they have become damaged themselves. The weather is another contributing factor, damaging the windows over time and then exacerbating the issue if there are any minor damages.

As with all glasswork, stained glass isn’t great at taking impacts, so it is vulnerable to physical damage. This could be accidental, such as from trees falling or extreme weather, or through vandalism/break-ins. Paintwork can also be affected physically, such as by brushing too hard. For this reason you should only use a soft brush to dust the windows and never wet-clean them.

What to do if stained glass windows are damaged

If you notice any minor damage to your windows, contact your inspecting architect. You may also need to contact an accredited conservator to assess the window, who will be able to give suggestions on how to proceed to avoid further damage and repair ay current damage.

Should any glass or lead break, such as through vandalism, collect the pieces and keep them safe. Again, contact your inspecting architect and a conservator for information on how to proceed.

How to protect stained glass windows

As with everything in the architectural world, prevention is often better than the cure. Regular checks, light cleaning and other small measures all go a long way to helping to protect stained glass windows, but there are more extreme measures you can take if an architect recommends it. These all take a lot of consideration, as there are upsides and downsides to each.

The first is metal guards. These are good for protecting against vandalism and break-ins. However, they are still vulnerable to smaller projectiles, can cause unsightly shadows and can cause staining to stonework if you do not take all of the appropriate considerations.

The second is polycarbonate sheeting. This is quite a common solution to safeguarding stained glass. That said, it is difficult to get right and there are many rules to follow. For example, the sheeting must be angled in a way to reduce reflections, fit the exact shape, not cover stonework and many more intricacies.

Finally, you could use Environmental Protective Glazing (EPG). This is when you move glass that is at high risk of deterioration from the environment away from the exterior. The stained glass can stay in its frame, but moved back slightly, with new glass added into the grooves as the new weather barrier. This is an extreme measure and should only be used for stained glass with specific historic significance and should only be carried out by a specially trained conservator. More information on conserving medieval stained glass can be found on the site for the Corpus Vitrearum Medii Aevi (CVMA). You can find an Accredited Conservator on the site for the British Society of Master Glass Painters (BSMGP) here or on the Institute of Conservation here.

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With over 30 years of experience in the industry, Munday + Cramer are perfectly positioned to work on ecclesiastical buildings. We are a multi-disciplined agency and thus can oversee entire projects, from surveying, procurement and architectural design, managing everything right through to the end product.

For more information on how the team here at Munday + Cramer can help in this process, or if you would like to find out more about our building surveying services, operating in Essex, London, Kent, Norfolk, Suffolk and across the rest of the UK then get in touch! Contact Munday + Cramer today on 01245 326 200.