STAINED GLASS

With sensible maintenance, traditionally made stained glass can be extremely durable. But common problems can include structural failure due to insufficient support or, where stained glass is set into opening casements or doors, the repeated movement can, over time, loosen the lead network and cause breakages in the solder joints and the glass. Leaking windows may be treatable without taking them out of their setting, by re-grouting them with a glazing cement by a specialist glazier.

Accidents are another major cause of damage, but if a piece of glass is broken it can often be repaired by edgebonding, thus retaining as much original material as possible. Even where fragments are missing, one should consider replacing only the missing section rather than the whole piece. In most cases, a skilled glazier or glass painter can replicate lost pieces – particularly if there’s a high-resolution photo of how the window was before.

The most important maintenance issue for stained glass windows is their structural integrity

– so check the windows are well supported through saddle bars, that the tie wires between the glazing and the bars are all present, and that the windows do not rattle and leak. Where ancient stained glass shows corrosion damage, the best way of preserving it is to introduce environmental protective glazing, with advice from a stained glass conservation specialist, as bad protective glazing systems can actually cause harm.

Clean stained glass as little as possible! Too much pressure while cleaning can break glass and loosen the glazing cement that makes the window weathertight. When cleaning, use only water, no detergents that could affect the glazing cement and the lead. Vinegar-based products attack the lead and can produce toxic lead carbonate.

Some damage can be repaired in situ. Individual broken pieces of glass can usually be extracted from the surrounding lead profiles and be replaced by carefully dressing the flanges of the lead back and using glazing putty to seal around the new piece. However, where the lead network has been torn or is distorted, the glazing will usually have to be removed for repair.

Buildingconservation. com is a good resource for reputable businesses. If the stained glass in question is very fine historic glass, the Institute of Conservation has a database of accredited conservators (conservationregister.com). Of course, your local specialist glazier may be just right for a simple repair of a Victorian or Edwardian domestic panel. Ask for before and after photos of their work, which can be telling. thecathedralstudios.com

RIGHT Two domestic windows that The Cathedral Studios made for Strawberry Hill House, which were made in the 18th century but lost in the 19th century. They were recreated from tiny watercolours, using other examples of the original artist’s work as a guide.