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Stained Glass & Other Starring Roles

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STAINED GLASS SPECIAL Stained glass and leaded light windows are specialist products but do not exist alone in any setting.  There are other associated trades and materials that are often required to make a window function usefully.  The main supporting role is played by metal.

 LEAD

The use of metal products is very important if a window is going to last.  Lead is the most obvious and the ‘H’ sections used for assembling a leaded window can be of various sizes and profiles, depending on the thickness of the glass and the design of the window.  A length of lead is called a ‘calme’ and is derived from the Latin word ‘calamus’, meaning a reed.  Lead calmes were originally made by lining up reeds in a shallow box and molten lead poured over them, resulting in lengths of lead with a groove along each side into which the glass would fit.  Now, lead is milled or extruded which is both quicker and more precise.  This lead is capable of lasting for an average of 150 years depending on weather exposure and support systems such as glazing bars.stained-glass

SUPPORT SYSTEMS

Without the support from glazing bars, a leaded window would sag and distort under its own weight.  Simple internal glazing bars have replaced much of the external ‘ferramenta’ over the years but this has been halted by the efforts of conservation practices.  The external ferramenta is a system of horizontal ‘saddle bars’ which are shaped to slot over vertical ‘stanchions’.  Copper tie wires soldered to the glazing are then twisted around these, holding the glazing in place.  Made of iron, these external bars are prone to rust within the stone but can be retained by ‘tipping’.  This involves cropping off the ends of the bars then welding on a non-ferrous metal of the same sized section.

CASEMENTS & HOPPERS

stained-glassAgain, being made of ferrous metals, these are prone to rusting and require overhauling to keep in working order.  Due to our churches being under ventilated, many have had new opening casements installed.  These can be made of mild or stainless steel or other non-ferrous metals and painted or powder coated.  Various mechanisms and pulley systems can be used to operate them as some will require operation from ground level while the window is 25’ up in the clerestorey.

ISOTHERMAL GLAZING

The rare pieces of mediæval glass found in our churches are now in such poor condition that they need protecting from the elements if they are to survive.  The pitting and white spotting usually seen on the outside of this glass are caused by chemicals leaching out of the glass in exchange with chemicals from the atmosphere mixed with water.  To prevent this, the glass has to be protected from the rain on the outside and from condensation forming on the inside.stained-glass

To achieve this, the glass has to be removed, protective glazing fitted in its place and the delicate glass reinstated forward by an inch or so and ventilated to the inside of the building.  For entire windows, the ancient glass can be fitted into manganese bronze frames and fixed to the inside of the mullions, leaving the protective glazing (glass, polycarbonate, laminated or toughened glass or simple leaded lights) to bear the brunt of the weather.  This can also be carried out for the benefit of individual pieces of glass which can be fixed proud of its supporting glazing, leaving an air gap between it and its protective glazing.

 

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