The paling of windows or other openings by using an assembly of pieces of glass has been known since Antiquity: fragments of coloured glass has been found in Pompei, Herculanum, Rome and other sites of the Roman Empire.
The medieval stained glasses were most probably developed from cloistral stucco, stone or wood, with geometrical or arabesque motifs, enchasing glass mosaics - a technique still prevalent at the time in Islamic art.
In the Occident, the art of stained glass, initially essentially religious, achieved its golden ages in Roman and Gothic times, and then during the Renaissance, before falling to a certain extent into disgrace at the French Revolution.
Resurrected by the style of the times at the end of the 19th century and at the beginning of the 20th century with the advent of Art nouveau, it today enjoys a key role in contemporary art and architecture.
Indeed, as in the case of many public and private buildings, the majority of modern churches have been bestowed since the last century with stained glasses often more decorative and abstract rather than religious, in which the colour and the texture of the pieces of glass plays an important role.
The craft of stained glass, described in extensive detail for the first time in history in the treatise on the artistic crafts, Diversarum artium schedula, written at the beginning of the 12th century by the monk Théophile, has changed little over time. Already in the 12th century a solution of iron oxide filings (today’s equivalent of grisailles) was used to decorate the stained glasses; once the painting was dry, the stained glasses were covered with lime and placed into a wood-fired oven, where they were exposed to a temperature just under their point of fusion. This is very much what we do today for painted glass. The cement, used to make the stained glasses water resistant and waterproof, was made from a mixture of ash and linseed oil; today we use a mixture of whiting and linseed oil.
In the 19th and 20th centuries, with the appearance of new materials and technological innovation, the process of making stained glasses and the working of the glass were significantly changed. However the glass master craftsmen, conscious of preserving the traditions handed down, continue to use the traditional means and methods that the new processes and modern machines cannot equal.
