The science, history and making of stained glass
Stained glass is a unique art form in that it is illuminated by transmitted light, either from the sun or an artificial light source. In situ, stained glass windows become animated through the movement of the traversing sun as well as the weather’s interaction, with clouds changing the light on a whim. The transmitted coloured light brushes across the fabric of the building as it has done for many centuries, visible today to the passive onlooker in the exact same way as it was when first built.
The religious significance of stained glass is largely lost to us today, but to emphasise its original importance, Bishop Guillaume Durand de Mende stated around 1300 that “stained-glass windows are divine writings that spread the clarity of the true sun, who is God, through the church, that is to say, through the heart of the faithful bringing them true enlightenment.”
Some 300 years later, Pierre de Roissy wrote, “The stained-glass windows that are in churches and through which . . . the clarity of the sun is transmitted, signify the Holy Scriptures, which banish evil from us and enlighten our being.”
The link between churches and the sun remains true even when there is no stained glass. When touring with the Summer Fields Chapel Choir in 2006, we sang in Vézelay Abbey, northern Burgundy, France. This stunning Basilica together with the hill upon which it sits, is a UNESCO World Heritage Site. Beyond the impressive proportions of this Burgundian Romanesque architectural masterpiece, there is a striking purity. I was surprised by the lack of stained glass: it is lit entirely through plain glass.
© Summer Fields Chapel Choir (2006) Fauré: Cantique de Jean Racine Op 11, Vézelay Abbey
While there, I read that it was not until 1976, more than eight centuries after construction, that the reasoning behind the orientation axis of the Basilica was rediscovered. At midday on the summer solstice, the light coming through the southern clerestory windows creates luminous sports that exactly locate in the full midst of the nave. To quote from Father Hugues Delautre, in the absence of coloured glass, “the builder, fascinated by the beauty of the universe which he recognises as the work of God, erected this vestibule to Heaven in imitation of God who created with order, measure and beauty.”
In medieval times, windows, stained glass or otherwise, were essential to the churches, illuminating the building and the people within, both literally and spiritually: in the eyes of the worshipers, they allowed the light of God into the church. At a time when few could read, painted windows were used to instruct people in the Christian faith and encourage religious devotion. Many windows illustrated scenes and stories from the Bible and the lives of the saints, who were revered both as a source of help in everyday life and as mediators in Heaven. With the magnificence of the stained glass providing an indication of wealth, as a gesture of philanthropy, rich donors, anxious to be remembered in the prayers of the faithful, often paid for the expensive windows.
Making a stained glass panel (2010) Victoria and Albert Museum
The term “stained glass” encompasses three different processes: colouring, staining and painting, each one complex and requiring the application of many skills. The glaziers who made these windows did not themselves make the glass, this was the job of the glass-makers. Glass manufacture was hot and dangerous work that required great skill and knowledge. Glass-makers knew and jealously guarded the glass recipes and furnace conditions needed to make a myriad of colours. They would mix the raw materials in clay pots heated with wood fires and then manipulate the resulting viscous liquid with metal and wooden implements.
Glass-makers would supply sheets of coloured glasses to the glaziers to create their windows. The process of making a stained glass window begins with the artist’s sketch, known as the vidimus (Latin for “we have seen”), but today more commonly referred to as the “design”, such as Henry Holiday’s example to the left. The vidimus was then drawn to full scale (known as a cartoon) on a whitened table top. The panes of coloured glass would then be cut to shape, placed on the cartoon. Over the years, several types of paints and stains have been developed to further enhance the stained glass designs. For example, a silver nitrate stain producing a yellowing effect has helped to enhance borders and haloes. A stain called Cousin’s rose was also developed, enabling artists to enhance individuals’ flesh tones.
As a final step, the window pieces are slotted into H-shaped lead (calmes). The joints are then soldered together and an oily cement is inserted between the glass and the dividers to ensure stability and reduce any potential rattling.
Once almost solely confined to medieval churches and chapels, stained glass windows spread into guildhalls, hospitals and manor houses thanks to wealthy patrons who could afford the luxurious coloured glass windows. During the 19th and 20th centuries, stained glass windows became popular in other places of worship, together with civic and domestic buildings. In more recent times, it has been used to form part of the main structure of corporate buildings, hotels, community centres and shopping centres.