Restoration/Conservation/Reconstruction: a discourse
The Burra Charter, an International Guide for the Restoration of Monuments, recommends (as I understand it) that when new items are added to old and made to look like the old, then it should be clear, in some way, which part is new and which is original. In practical terms this will always be the case as it is virtually impossible for one artist to imitate another artist's work with such exactitude that the two are indistinguishable (excepting extreme cases of genius, which we generally call forgery).
There is, as you can imagine, much debate and controversy over these issues. Conservators, Restorers and Artisans seldom agree. There is a school of thought, persistent in this country, which holds that every remnant of the fabric of the window should be retained and re-used and that the painting of new glass to replace old damaged glass is anathema. I do not subscribe to this view.
Much of our heritage material, particularly dedicated windows, memorialises those who persist in living memory. And even when this is not the case, the windows are certainly referred to for historical information. So this information needs to be maintained and preserved. When an inscription for instance is no longer legible or a face is cracked in three or four places I have no qualms about painting a replacement piece of glass. I make every effort to match the original as exactly as I possibly can but there is naturally going to be some minor variation. This variation itself becomes a part of the history of the window.
To Relead or Not ?
The principal of "Minimum Intervention" is definitely a useful guide but I don't believe it should be the rigid, unbending rule by which repair work is carried out. Each case must be considered on its merits.
In restoring and repairing damaged windows a craftsman will often come across earlier repairs, sometimes expertly carried out, sometimes of very dubious quality indeed. Often the repair was not obvious until the window is on the bench and so a decision has to be taken as to how to proceed. Usually I will leave it intact, re-using the work of that earlier artisan but sometimes it's best to make it new. The bottom line is always: what is best for the window?
Especially absurd in my view is the opinion that old lead in a window which is failing should be retained wherever possible. This approach recommends that new solder be applied to the old lead joints which have given way and that the window not be stripped and rebuilt, since the lead itself is of historical significance.
While there is some merit in the idea that old lead was made differently to modern window lead (milled vs extruded/different standards of smelting) we have to acknowledge that lead does deteriorate and does have a limited life span. It will oxide and sag over time, losing its structural integrity. The crystalline coating of oxide which develops on the external surface of a lead calme will act as barrier to further oxidation for a period of time. However, with the constant flexing caused by wind pressure solder joints will eventually fail as the fabric of the softer lead tears away from the stronger tin/lead alloy which forms the solder.
Milled vs Extruded Lead
Milled lead is certainly available today although there are very few Australian studios milling their own lead (only three to my knowledge: two in Sydney and one in Perth). As far as I know the only commercial supplier of milled lead calme is in Belgium. There is still much debate over the relative merits of milling vs extrusion and the actual quality or purity of window lead available commercially. Do those studios which carry out their own milling also carry out independent metallurgical assay of the lead produced? Is it a given that 'pure' lead is in fact better or longer lasting than lead with a certain content of antimony or copper? I have even been informed that all lead produced 'these days' is contaminated with aluminium and consequently self-destructs. This is possibly a fertile area for further study.
There is also an interesting phenomenon which appears to be endemic to Australian climatic conditions. It seems that when exposed to the extreme heat of direct Westerly sun lead calme will obviously expand but not so obviously will refuse to contract to its original state. The lead stretches and 'grows' and over the years this expansion in the metal fabric of a window will cause significant buckling, both inwards and outwards, sometimes causing the lead to tear away from any copper ties which might be securing it to internal steel reinforcing rods. This is an effect additional to the natural sagging of a leadlight under its own weight.
Corrosion of Steel
Steel frames also corrode and with such corrosion will expand, putting additional pressure on the leaded fabric of the window and also the stone or masonry in which the frame is installed. All of these factors must be considered. Corrosion needs to be arrested before too much damage is caused and sometimes frames must be removed and completely replaced or at least refurbished, with new sections of steel being welded in to replace those beyond salvaging.
Obviously this will require the removal of the stained glass panel from its frame and that process will itself place considerable stress on the leaded fabric, no matter how carefully the window is handled. The strong possibility that the leaded panel will collapse once removed from its frame and transported to a workshop must be taken into account when determining an appropriate course of action for refurbishment.
The majority of Australian cities are coastal and proximity to the ocean is a significant factor in the progress of steel corrosion. But it's not the only factor and I have seen some country churches where the steel frames have corroded to a point where they no longer function and are themselves the cause of major damage to both the stained glass window and the building.
Perhaps it could be said that steel is not the best choice of material for window framing in a coastal city. Certainly stainless steel should be considered as an option if funds allow. Any new steel work, whether newly fabricated or refurbished, should be either galvanised or heavily primed and painted before reinstalling into the building in order to protect the metal and prolong the life of the frames.
So there comes a point in the life of a window when a decision must be taken to remove the window from its opening in the building, strip it down, salvage all the glass and rebuild with new lead. Carrying out this sort of major renovation has the added advantage that any broken glass in the window can be properly replaced on the bench rather than 'in-situ'. An in-situ repair is only ever "adequate", at best. More often than not these repairs have been carried out by inexperienced tradesmen, with less-than-satisfactory results.
Re-leading stained glass windows every 80 - 100 years or thereabouts should be considered a normal part of the maintenance program of a building. A well-built window protected from the weather may last a good 150 years. Equally a poorly constructed door panel with little or no reinforcing and constant slamming might fall apart after only 25.