Cyclic Maintenance


Copyright © 1996-2018  Geoffrey Wallace Stained Glass


With proper cyclic maintenance a stained glass window can survive, depending on its aspect and corrosive environment, for several centuries before expensive re-leading is required.  On older windows, maintenance works should be carried out about every 25 years or whenever the window reaches stage 1 of deterioration. The works should only employ traditional methods and materials and care should be taken not to introduce any modern chemicals, detergents or silicones as these can not only damage the glass or lead but permanently destroy the regenerative nature of stained glass.    Maintenance work is typically carried out in situ, with no need to excavate the windows.  .A standard maintenance programme would include the following work:


Cleaning is the most obvious procedure in the maintenance programme but needs to be undertaken with extreme care as many older windows have unstable glass paint which could be inadvertently removed by using chemicals or harsh cleaning methods. Although usually unseen from the ground, internally the windows have a build up of dust and grime that has congealed over many years of condensation and leakage along with deposits of calcium carbonate that has leeched from the leadlight cement.

Externally the glass can develop a dull patina composed of soluble silicates and/ or pollution deposits. If not removed this rough patina serves to trap other airborne chemicals which over time will corrode the glass. The effects of cleaning are spectacular beyond expectations and can dramatically lift a jaded interior.


This is the most important maintenance procedure of all as the new cement not only waterproofs but re-sets the window into  a single, solid unit once again. After removal of any old loose cement, a new regenerative cement mixture is liberally applied to the external lead calmes forcing cement and linseed oil up and under the flanges of the calmes. The excess cement mixture is left on the windows to allow the old cement to suck in the new oil and more mixture is applied until suction is complete before being cleaned off. 


All ferramenta, including saddle bars, casements and vent frames are descaled before applying rust converter, to halt further oxidation, and then re-painted. If saddle bars have rusted in the masonry frame they will be removed and replaced or cold galvanised where they enter the frame. Hopper vents and casements are repaired or replaced as necessary and are re-sealed with glazing putty as required.

Copper Wire Ties

Copper wire ties are soldered to the stained glass panel in order to attach the steel saddle bars that serve as reinforcement against wind pressure or buckling of the window.  All existing tie wires are checked for breakage or fatigue and replaced if faulty.

Lead Matrix

On otherwise stable panels, broken or cracked joints are re-soldered in situ. Where joints have fatigued but not broken due to buckling or movement, discretion is used as to the need for re-soldering taking into account improved structural support after maintenance works.


Mortar fillets to the masonry glazing channels are checked for soundness and water proofing and any unstable fillets are cleanly hacked back to stable mortar.  The channels are re-pointed with soft lime putty mortar to allow for safe removal of the window, if necessary, in the future. Cement based mortar or glazing putty should never be used to seal stained glass windows in masonry frames.  

Buckling and Bulging

Severe buckling will require excavation for straightening or partial re-leading of the panel on the work bench.  Minor buckling will be left alone but should be monitored in the future.

Glass Repair or Replacement

Minor glass cracks that remain weatherproof and pose no threat of dislodgement are left untreated. Severe glass breaks in leadlight windows are replaced with glass similar in texture and colour to the original. All broken glass in painted and stained windows is retained and repaired, where necessary, using approved, reversible, heritage conservation methods for stained glass. No glues, silicones or chemicals should be used.

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Frame Maintenance and Rehabilitation

Masonry, timber or steel frames are treated, as necessary, for decay and waterproofing to ensure that they also can last as long as the stained glass window.