Why Repair Beats Replacement

A leaded window is not a single object so much as a structure: hundreds of small panes held together by strips of lead, tied back to iron bars and bedded into a stone opening. Age it and it sags, cracks and loses its putty. Yet almost every part of it can be mended rather than remade. In a parish church, the instinct to replace a "worn out" window should be resisted. Original glass, however plain, carries the slight irregularities and colour shifts that make old churches feel alive, and it is irreplaceable once swept into a skip. Repair is usually cheaper than the parish expects, and it keeps the building's historic character intact.

How a Leaded Window Is Put Together

Understanding the components helps when discussing work with a craftsperson. The main elements are:

• Quarries — the small panes, often diamond-shaped, sometimes square. Medieval glass is hand-blown and slightly uneven; Victorian glass is thinner and more uniform.
• Cames — the H-sectioned lead strips that hold the glass. Earlier cames were cast; later ones milled to standard profiles.
• Solder joints — where the cames meet, usually a tin-lead solder, which should sit neatly rather than in heavy blobs.
• Saddle bars — horizontal iron bars running across the window, giving the leadwork support.
• Ties — copper wires or lead strips binding the panel to the saddle bars.
• Putty and pointing — linseed oil putty bedding the glass into the cames, and lime mortar where the window meets the stone.

What Usually Goes Wrong

Lead is soft and slowly deforms under its own weight. Over decades, a window "creeps": the lead stretches, the panel bows and the whole lattice sags. Corrosion, especially near the saddle bars where moisture collects, thins the cames until cracks open along them. Putty dries, shrinks and falls away, leaving glass loose. Iron saddle bars rust and expand, sometimes fracturing the very glass they support. Cracked quarries often follow distortion rather than come out of nowhere, so replacing a cracked pane without addressing the sag will simply produce another crack a year later.

Diagnosing Before Touching the Glass

Good conservation begins with understanding. A conservator will photograph each window, record the pattern and the position of original glass, and test by hand how much the leadwork moves — gently. The condition of the pointing, the drainage of the surrounding stone and the ventilation of the interior all matter: a window that streams with condensation will corrode its lead from the inside out. Sometimes the real repair is not the glass at all, but clearing a blocked gutter, mending a leaking roof or repairing a broken vent above.

The Repair Process on the Bench

Panels are removed in sequence and numbered so they can be returned to the same positions. On the bench, the window is laid on a glazing easel. Old putty is picked out dry rather than softened with heat or chemicals. Each quarry is freed, cleaned with soft brushes and a little de-ionised water, then set aside. Cames may be straightened and reused where the lead is sound; where it is cracked or thinned, new lead is cast or milled to match the original profile rather than swapped for a heavier modern section.

Glass edges are dressed with a grozing iron or fine file to suit the cames. The panel is reassembled on a wooden frame, solder joints are made cleanly, and the glass is bedded with linseed oil putty worked in warm and pressed back with a stiff brush. Finally the panel is tied back to cleaned, painted saddle bars, rehung in the opening and pointed with a lime mortar matched to the surrounding stone. The aim is a window that is sound, watertight and visibly old — not one that looks factory-fresh.

Caring for Leaded Windows in the Long Term

Once repaired, leaded glass asks little. Keep the interior ventilated so condensation does not sit on the cames, and never wash a window with anything stronger than water and a soft brush. Wire guards are worthwhile on low windows vulnerable to footballs and ladders. A quinquennial inspection by an architect or conservator will catch the early signs — a single cracked quarry, a loose tie, a dribble of water down the stone — while they are still cheap to put right. Handled kindly, a leaded window will outlive everyone who tends it.