Making stained glass windows

The first evidence of stained glass in England is from Bede, writing in 680AD, who says craftsmen were brought from Gaul to work on St Peter’s, Monkwearmouth, and St Paul’s Jarrow. Fragments of coloured and flashed glass from excavation of Saxon monastic buildings at both these sites, support Bede’s writings.
Stained glass was fairly widely known by 12th century, but between 6th and 12th century, there is little evidence of it in England, much more so in France. Most stained glass was very symbolic (eg garden of Eden represented by one small tree). Glass making is a skill in itself, and glass makers were often situated close to one of their raw materials (e.g. sand or firewood), rather than near the people who put windows together. Finished sheets or crowns of glass were bought by weight rather than area. Coloured glass was more expensive, and was imported into England. Usually coloured glass cost at least twice as much as plain, sometimes more. Plain glass could be made in England.

Basic ingredients

Glass can be made from just sand (silica), however this needs very high temperatures, so usually other ingredients are added to reduce the working melting temperature and improve the properties (as is still done today– the lead crystal glass that makes fancy wine glasses is different to the borax glass that makes oven proof dishes). In the past it was rare to get pure silica anyway. Roman glass had the ash from sea plants added, giving “soda glass” (as it was rich in sodium). From about 1000AD onwards, ash from burning wood (potash) was more often used. This is more rich in potassium, but makes the glass more susceptible to weathering and decay. Theophilius, wrote “On Divers Arts” around 1120, and describes the arts of metalworking, painting, and making stained glass windows. In this he gives a recipe for glass, specifying the types of trees the potash should come from as well as the metal oxides that could be added to give colour.
Making glass needed a lot of sand and a lot of heat, thus a lot of firewood, as well as the extra ingredients like potash. Making a sheet of glass was usually done cylinder method (a cylinder is blown, both ends removed and the resulting cylinder split and flattened into a sheet), and the crown method (a bubble is blown, transferred to a hot iron rod - the pontil - pierced and spun out yielding a round sheet but with a pontil mark in the centre). Thus, sheets were usually around 2ftx1ft or smaller. “Pot Metal” glass is glass which is coloured all the way through as the colourant was added when the glass was in the melting pot. Red glass, made with copper, tends to be opaque, so best if it is “flashed” i.e. a bubble of clear glass is blown and dipped into a crucible of red, giving a thin coating of red on the glass. Glass sheets made like this then need to be annealed.

Colour

Colour in glass arises from adding metallic oxides during production:

Blue: copper or cobalt
Green: copper or chromium
Yellow: ferric oxide or uranium
Purple: manganese
Red: copper, selenium, or gold
Brown/Violet: nickel with different base glasses

Window structure

Windows taller than 3 feet high need support from saddle-bars set into stonework on either side about 12inches apart. Larger windows also need vertical support. The position of this metal work must be considered from the beginning. Pieces of glass are fitted together using lead calms (pronounced “cams” or “cames” in USA). These have an H-shaped cross-section into which the glass slots. Once all the pieces have been put together, the lead joints are soldered on the front and back of the window and the space between the glass and lead is filled with a putty to give strength and to waterproof the window. It is then fixed to the saddle bars using copper ties which are soldered in place. This method of making a window makes it slightly flexible, so they are little more resilient to movement of an old building than the equivalent single pane might be.

Stained glass before restoration

Designs

To make a stained glass window, the image is first planned out. In the time of Theophilius this was done on a white-washed table, the image, known as the “cartoon”, was drawn on the table, showing where the lead should go, and sometimes where the tracery lines (the lines of shading that would later be painted onto the glass) go. Analysis of one surviving medieval table has revealed several layers of drawing. Paper was more readily available in Italy, so some of the earliest paper cartoons are from Italy, though even in the late 14th century, a writer describes how to glue sheets of paper together to make sheets large enough for the cartoons. Paper also allowed designs to be stored and reused. In 1503, the will of York glass-painter, Robert Preston left “all my scrowles” to Thomas English. Paper also allowed other artists to make the cartoon that a glazier then made up: Albrecht Durer and Hans Holbein the Younger drew many designs for stained glass that others then made up and an easily portable cartoon allows artists to supply the cartoon to the glass-painter.

Shading

The type of picture that can be made has varied over time. Initially, windows were mosaics of glass with some detail painted on using an opaque paint (which then had to be fired onto the glass). This allowed lines and shading to be added, creating, for example, the effect of folds in material. Flashed glass (where a layer of colour was added to plain glass when it was made) could also be scratched to removed colour. Theophilius also mentions that glass “jewels”(pieces of coloured glass) can be fixed on using a thick layer of glass paint between the jewel and the window glass, then firing it together.

Silver Stain

In the 14th century, silver stain, which had been used since the 8th century to decorate Islamic glass vessels, began to be used on windows: a silver oxide is painted on, and when it is fired, the silver ions migrate into the glass and become suspended in the glass. These give a yellow effect on clear glass, and depending on the compositions of the glass and the stain, the firing temperature and the number of applications, it can vary from a pale yellow to a deep red, When fired on blue glass, silver stain can appear green. Silver stain must be fired at a lower temperature than the opaque glass paint, so has to be done after the line and shading detail. However, in order for the silver ions to move into the glass, the stain must be in contact with the glass (not paint), so was sometimes done on the reverse side of the glass.
Silver stain gave a big advantage, as, together with the opaque paint, it allowed a lot of detail on one pane of glass (eg a head, with face, hair and crown detail, could all be done on one piece of glass).

Glass paints

Around the 16th-17th century a new range of enamel pigments that could be painted onto glass were found. These are intensely coloured ground up glass which is painted onto the base glass and become fused to the glass surface. Although they are not opaque, they do not produce as transparent an effect as the pot-metal glass. Enamel paints meant colours could be painted on plain glass, and windows started being made from regular rectangles of glass. However, there was still a limit to how large these could be made, and too large a piece could break when put into a window. Thus, many enamel-painted windows are done on a regular grid of glass.

Mediaeval design

12th Century
Most stained glass was very symbolic (e.g. garden of Eden represented by one small tree).

13th Century
Slightly more narrative elements,( e.g. Canterbury has windows that need to be “read” left to right, starting at the top), but still only those needed to tell the story (e.g. no landscape except when a ploughed field indicates a man is a sower, in the Sower’s parable).

14th Century
Increase in population at end of 13th century meant labour paid less well. The Black Death (1348-9) reversed this trend and, having affected good and bad, may have diminished faith in the church. Some thought that one could buy their way into heaven, e.g. by buying pardons or something for the church, e.g. a window. Some windows started to name or even depict the donor, as well as more secular subjects (more akin to those illustrations found in the margins of illustrated manuscripts). Heraldry had become a more common subject, sometimes in the hope people would pray for those therein.
Silver stain was popular as it meant that larger pieces of (cheaper) plain glass could be used (e.g. a head with face, golden hair and a halo could be done from one piece). London had a guild of glass makers by 1328.

Renaissance design

15th Century
William Caxton (1421-91) started printing books, illustrated with woodcuts. England became prosperous due to the cloth trade and the want for English wool. Families who had become rich this way started financing rebuilding or embellishment of their local church, thus (they thought) saving their soul (and perhaps outdoing the rich man in the neighbouring town).
Annealing or jeweling, in which chips of coloured glass were fixed with flux and fired onto the main glass section, became popular. Woodcuts, in which shading was done via stipple (dotted) shading may have influenced stained glass, as stipple shading with paint became more common than the smear shading used previously. Designs could now be made on paper or parchment rolls, rather than drawn on a table, and thus were easier to keep, transport, and reuse.
Images began to include more allegorical figures (e.g. Strength, Death, Beauty), as well as more secular elements like heraldry, or even contemporary events (a church at Little Malvern has a window with Edward VI’s queen and children, as they took sanctuary there when Edward fled to France). Many “Doom” windows, showing the end of the world, were also made.

16th and 17th Centuries.
The rise of Protestantism abroad meant many craftsmen moved to England. However, Henry VIII’s split with the Catholic church and the dissolution of the monasteries, meant a lot of stained glass was destroyed. In 1636, the Thirty Years War resulted in destruction of the glass furnaces in Lorraine, and the availability of pot glass was reduced. There was some revival in the early 17th Century, as the use of enamelling allowed more colours to be put onto plain glass which allowed windows to be made to look like clear windows looking out onto a landscape (though the landscape was enamelled on). This matched the rise of Renaissance art, which promoted perspective and glimpses of landscape. Later, because of the Civil War and Commonwealth (1640-8), there were few sources of funds for stained glass, and much was destroyed (because it was religious, and thus condemned by Puritans or,denounced as Royalist if it was heraldic). There was some re-emergence of the craft at the end of the 17th century, and the first trade-cards for glass painters appeared.

18th Century

Church of England continues to lose its hold over society to science and dissenting churches (e.g. methodists), and a growing belief in pantheism (where God was to be found in the forces of nature). Many stained glass windows are now copies of paintings. As there was little pot glass being imported, some was now being made in England. Stained-glass windows were still being destroyed (almost as much as in under Henry VIII and Cromwell), though now the reason was that it was out of fashion.

19th Century

A revival of the craft due to artists such as William Morris. Early 19th Century stained glass windows often tried to be more like paintings with as little lead-work as possible, and were criticized for trying to imitate what was achieved in oil paintings, and for replacing mediaeval windows in mediaeval churches, with stained glass which did not take account of the architecture. One panel exhibited at the 1851 Exhibition featured St Michael and the dragon and was a record 9feet by 5feet. Charles Winston, though a barrister by profession, rediscovered the mediaeval constituents of 12th and 13th century glass, and worked with Powell’s glassworks to reproduce it. Some felt this a better glass, the modern glass letting in more light, thus being too bright.

The workshop of William Morris and company was founded in 1861. Morris believed designs for stained glass windows should be simple, bold, with the minimum of shading, and enlivened with colour. Ford Madox Brown, in Morris’s Company, emphasized the dramatic nature of the medium, and the use of strong lead lines.

Designs in St Giles

There are examples from at least three stained glass firms in St Giles. The first windows to be done were those on either side of the nave, and depict a saint, or a worthy person, from each century, starting at the 1st century with St Clement. These were designed by Robert Turnhill Bayne of Heaton Butler and Bayne (in his designs, Bayne often included at least one figure with his features and long beard). The windows on the south side (nearest the main door) were installed in 1888, those on the north side were a few years later. The firm had worked to understand how to reproduce the colours in mediaeval glass, and were known for their wide range of coloured glass. The window above the door in the west end continues the theme of having a person from each century, showing Bishop Gore who died in 1932. In 1917 Bishop Gore licensed 21 women as lay readers, and unheard of event at the time! His window is by Ninian Comper, who designed many other parts of St Giles’ church interior. The windows in the Lady Chapel and Sanctuary are by Charles Eamer Kempe, and later by Tower Kempe (on his death, Kempe left his company to his cousin, Walter Tower). Kempe’s signature sheaf of corn can be seen in his windows, those by Tower Kempe have a black tower on the cornsheaf. Kempe’s work is often a little less vibrant than that of Heaton Butler and Bayne, showing backgrounds of white glass with architectural details (including intricate canopies and draperies) enhanced with silver stain.

With thanks

Much of the work on the restoration of St Giles has been made possible through funding by the National Lottery Heritage Fund