Caring for Leaded Lights

Leaded glass is the oldest glazing technique still in production today and is widely used across the world. As a method of glazing and as an artistic medium, leaded glass is both extremely versatile at the same time as being functional and durable. Given the right conditions leaded glass can and does last for hundreds of years meaning that there is a great deal of very old glass remaining in many older properties, often unnoticed and at times underappreciated.

Owners of historic buildings are usually lovers of historic buildings, but with that appreciation comes a level of responsibility, as well as seemingly endless repair bills. Special buildings call for specialist craftsmen and women but drawing upon their knowledge, training and experience inevitably costs money. It is for this reason that the issue of maintenance is so high on the agenda for people caring for such buildings. Anyone who has taken note of SPAB’s National Maintenance Week each year (see or examined the costs of regular maintenance versus large-scale programmes of restoration will be fully aware of the financial implications of ignoring day to day upkeep.

Keeping up with the maintenance doesn’t mean that your property has to become a money pit. Most maintenance is simple – clear the gutters, unblock the drains, replace slipped slates. Other maintenance issues are less straight forward, but with a little knowledge of the subject you can still stay on top of most things. Leaded light windows are one of these things and the following examination of the materials used, the way in which they are built and the way in which they can be repaired should be of use to anyone involved with historic buildings glazed in this way.

Leaded lights are very simply built. The origins of combining the H-section lead (known as “cames”) with glass came about due to glass production techniques only allowing small sections of glass to be made. Combining the two materials meant that bigger spaces could be glazed. In many ways, the limits of early glass production led to the creation of the stained glass industry as many of the worlds finest stained glass windows would never have been produced if the leading of glass had not been invented. Fortunately for historic home owners, painted and stained glass is quite rare in all but the grandest of historic houses.

New leaded lights have an average life expectancy of around a century. In the right conditions, leaded glass has lasted several hundred years and thanks to more widely available expert conservation work, there is still a surprising amount of medieval leaded glass still extant today, principally in our church buildings. However, most leaded glass fails long before this and there are a number of signs of failure that you can look for.

Firstly, examine the leadwork. In its best state, each lead came should be flat, smooth and straight at the edges and the panel as a whole should be the same. One of the first signs of a problem is almost always presented in movement in the leadwork as a whole or in individual cames. Individually, the lead cames can disfigure by becoming furrowed at the edges, raised, bowed or otherwise misshaped thanks to years of expansion and contraction. At the same time, the entire lead matrix can move as one, taking the glass with it and leaving the entire panel buckled and bellied inwards or outwards. Some movement is all part of the charm of older leaded light windows and minor movement is not in itself a major cause for concern. However, where this movement is more pronounced there is a danger of the force of the movement causing the glass to break resulting in the unnecessary loss of original historic fabric. Movement in the lead work also breaks up the cement which binds the glass and lead together, leading to ingress of weather. In severe cases, the same movement can cause the soldered joints in the leadwork to break apart leaving the whole panel structurally insecure.

The second thing to look at is the glass itself. Despite its inherent predilection for breakage, the glass is the least likely part of the window to fail of its own accord. Old glass is full of natural imperfections, sometimes so severe that actually seeing through it is very difficult. At the same time, it is these imperfections that make leaded light glazing really glitter and come to life. In most cases, it is quite possible to save original old glass from dilapidated lead cames. In our studio experience, it is very rare that we have to replace such glass, even if only a few panes or “quarrels” of the original glass remain. Keeping original fabric which still has life left in it, even if it is as small and seemingly insignificant as a single quarrel of glass, is important in maintaining the integrity of the building as a whole, so it is always good practice to retain the old glass. Similarly, leadwork should not automatically be deemed to be sacrificial as in certain cases it too can be repaired and retained.

Caring for the glass in leaded panels is quite straight forward. Day to day cleaning inside and out should normally be carried out using cotton wool and de-ionised water. Older glass and modern mouth blown glass is very susceptible to scratches, so take off rings and jewellery before cleaning. Don’t scrub, clean lightly and often, never use cleaning agents or abrasive cloths as both can damage the cement which holds the lead and the glass together. If in doubt, call any leaded light maker or restorer for help. Never clean painted or stained glass yourself – this should only be carried out by a specialist as such operations can present a minefield of problems.

Next, look at the more functional parts of the panel. Most leaded lights are held in place with ties. These are usually flat or round sections of wire in lead or copper. The ties are soldered to the panel at joints in a straight line across the panel and attached to a metal tie bar or saddle bar which is lodged into the frame or aperture at each end. The bars can run in almost any direction along joint lines, either in straight runs or wrought around more unusually shaped leadwork. Lead ties are normally folded around the bars and copper ties usually wrapped around and then twisted and folded at the ends. It is these ties that give a leaded light panel most of their structural strength against wind, bird impact or draw from opening doors for example. As part of any maintenance monitoring, it is always a good idea to check that the ties are attached to both the panel and the tie bar. The force of moving lead as outlined above can often cause the ties to detach leaving the panel unsupported. A good example of such failure was seen at Chester Cathedral in 2008 when clerestory leaded lights were torn inwards by the pressure draw caused when opening a pair of large doors.

Finally, check your frames. Leaded lights can be glazed into almost any type of frame, or directly into masonry apertures as seen in most church buildings. Significant movement to any aperture can spell disaster for leaded lights, although they are by the very nature more capable of coping with minor movement better than plain glazing. One of the biggest problems we come across at the studio is the effects of corroded metal frames on leaded light glazing. It is widely known that metal expands when corroding, meaning that the leaded light glazing is forced increasingly tightly into the frame over time. Eventually, something has to give and the pressure usually gets to the glass first, exerting enough force on it to smash it.

Similarly, where timber has swollen or masonry moved or delaminated, the stress upon the glazing can be immense, causing cracks and even wholesale shattering of sections of glass. Identifying these issues is again quite easy and some simple steps such as keeping metal and timber frames well decorated can be money or time well spent if it saves a much larger glazing bill. It is also a good idea to check metal frames for sitting water, either as a result of weather or condensation, something which if gathering to excess is also in itself damaging to leaded panels. Many metal casement windows will have small weep holes along their base to allow release of sitting water so make sure that they are not blocked with years of paint or bundles of dead insects.

With the right level of care, leaded light windows can serve any property well and will outlast most of us by quite some margin. Good practice in the repair of leaded lights will always involve the retention of as much of the original glass as possible and in some cases retention of very old leadwork. Cleaning is straight forward and maintenance checks very simple. When you do identify an issue such as those outlined above, there are plenty of traditional craftsmen and women in the UK who are highly skilled and capable of repair and restoration work, a number of whom are listed in the directory at the back of this issue.

Jamie Moore oversees a team of highly skilled craftsmen and women at Recclesia Ltd, specialising in the conservation and repair of historic buildings with in-house traditional skills including stonemasonry. lime mortars, metalwork and stained and leaded glass.