ABSTRACT
Stained glass has been an important medium for the illustration ofEuropean culture and history for over 1500 years. Stained glass windowsoriginally served an architectural purpose, being designed to admit light to the interior of the building through openings within the structural masonry. The medieval window comprised panels, lancets and traceries, each anchored into the surrounding masonry by iron ferramenta or saddle bars. As time passed, designers recognised the potential of this unique translucent medium and construction techniques became more sophisticated and the ambition of benefactors grew ever greater. The range of colours expanded and the H-shaped strips of lead, or calmes, which held together the separate pieces of glass became incorporated into the designs. In the great church architecture of the fourteenth and fifteenth centuries, stained glass became an essential part of the medieval multimedia experience.[1]
Strictly speaking, the term ‘stained glass’ refers to a specific glass-painting technique from the early fourteenth century, in which yellow stain was applied to clear glass. In practice, the term is widely used today to mean any leaded windows of coloured or painted glass. Several factors affect the body colour of glass, including the chemical composition of the raw materials, melting times and temperatures, and how the glass was cooled from the molten ‘pot-metal’ state.[2]
Glass has the paradoxical qualities of being both brittle and highly durable, able to survive for many centuries. Glazed artwork resists fading and weathering, and in general it is likely that original stained glass will out-survive any of its reproduced archival images. Yet, because glass is so fragile, it takes only a moment for it to be cracked or broken. Typical threats include damage from stone projectiles, birds, fire, weathering, acidic atmosphere, and condensation. It is therefore important to have visual records for historical and restoration purposes.
