The discovery of fragments of medieval window glass during excavations within the City Garage in Blake Street comes as no surprise. York is famous for its medieval glass, and those interested in this aspect of its history have been hoping for great things from the archaeologist. Our earliest reference to its use in the city dates back to the end of the seventh century. Eddius, in his Life of St Wilfrid, tells us that the bishop restored the Minster and ‘prevented the entry of birds and rain through the windows by means of glass, through which, however, the light shone within’; a singularly sensible explanation of the functional value of glass, and an idea to be developed by twelfth century theologians into a vivid image of the spiritual enlightenment of the soul pierced by the rays of the True Light. This idea found its fullest expression in the mysterious luminosity of St Denis and Chartres, an aesthetic which also pervaded the Late Norman Minster of Archbishop Roger, some of the glass from which has survived, reused in the present building. Wilfrid's glass is yet to be found, - indeed the church itself still awaits discovery - but what we might expect as glass similar to that excavated in recent years at Jarrow and Monkwearmouth, unpainted but in a wide range of most beautiful colours. Less sensational than the discovery of Wilfrid’s glass the City Garage may be, but it is nevertheless of tremendous interest and importance in throwing yet more light on the medieval glasspainters of York.

About 2,500 fragments of glass were found together in a pit, filled with rubbish in the late fifteenth or early sixteenth century. Many of them are smashed into very small pieces, but considering its long burial underground, the glass appears to be in remarkably good condition. Some of it is very corroded, with an accretion on the surf aces which renders it almost opaque. The majority, however, appears - to the eye at least - to be in a reasonably stable condition.

Glass, even when fixed in a window, is peculiarly vulnerable to moisture, which reacts on the alkaline content (potash was usually mixed with the sand in the Middle Ages) and causes the corrosion so often seen on ancient glass.

Over 90 per cent of the glass is white, mostly flat, and varying in thickness from about 1mm to 2mm. The colour varies between very clear and a green tinted ''white'' glass, due to the iron content. Yellow stain, from which our rather misleading modern term ‘Stained Glass’ derives, occurs on a few painted pieces. This technique, not discovered until the early fourteenth century, enabled white glass to be coloured yellow. A silver compound was applied, usually to the exterior surface of the glass, which turned yellow when fired, enabling the glasspainter to colour a figure's hair, beard or crown yellow, on the same white piece of glass used for the face. This gave much greater freedom to the glasspainter, who would previously have had to lead in separately any yellow colour he wanted. It makes its first appearance in York in some of the nave aisle windows of the Minster and its potential is perhaps most fully exploited in the three west windows, commissioned in 1338, in which white and yellow reign supreme.

About 4 percent of the glass is ruby, not made out of precious gems, as its name might imply (though as late as the French Revolution windows were being melted down in the vain hope of extracting valuable material). The colours (apart from yellow stain) were imparted to the glass in its molten state at the glasshouse, by the addition of different metallic oxides. This means that medieval class, called pot-metal because the metallic oxides were added in the melting-pot, is coloured right through its thickness, as opposed to the post- medieval practice of painting on white glass with coloured enamels, a method used in York from the last quarter of the sixteenth century right through to William Peckitt’s attempts to revive the art in the late eighteenth century, a kind of Gothic phase of the later ecclesiological and archaeological revival, when the pot-metal system was fully revived. If a pot-metal ruby, coloured through the thickness of the glass is made, it lets in virtually no light and appears black. The glass-blowers overcame this by inking a flashed- ruby; that is by adding a thin coat of ruby to white glass. The ruby from Blake Street is flat and even in colour. Different pieces vary in shade from a dark red to a thin pink. One piece is spoiled with a blue discoloration, due to contamination with blue glass during manufacture.

Blue glass accounts for a further 4 percent. It varies in intensity from a beautiful deep tone to a very pale shade. Two pieces are splashed with stain, which when used on blue glass, gives a greenish-yellow tint.

There are a dozen pieces of purple, again varying in tone, and one solitary piece of pot-yellow (coloured through the glass), which was much less commonly used after the discovery of yellow stain.

The proportion of the colours reflects standard practice in fifteenth century England, to be seen in the choir of the Minster and many of the parish churches of York. White glass, much cheaper than coloured, was used in much larger quantities. Often highlighted with yellow stain, it was used mainly for the figures and the delicate canopies which frame them, for borders, and for pattern-glazing in diamond shaped quarries - a cheap way to fill up a light. Red and blue were the other main colours. They were much used for robes and in heraldic shields, but they feature most as dark backgrounds on which the figures could be set off. Red glass could be used for fiery dragons, and pieces like the spoiled ruby could even be used special effects. A particularly fine example of this is the superb dragon on which St George tramples in a memorial window to Sir Richard Yorke (d. 1498) originally in St John’s, Micklegate, but now in the north transept of the Minster. Unfortunately the saint is a sadly truncated figure, due not to any power of the monster at his feet, but to the loss of the upper panel. Some idea of his original appearance can be obtained from the east window of Holy Trinity, Goodramgate (1470), which exhibits an earlier use of the same cartoon.

One of the most unusual features of the glass is the presence of a large number of edge-pieces from sheets of muff glass. These have a straight edge which is much thicker than the main body of the glass. The muff process was one of two methods used to manufacture window glass in the medieval period. The glass was blown into a cylindrical form (hence ‘muff process’), which was then cut down one side and flattened out. This method is described by the twelfth century German monk Theophilus in his treatise ‘De Diversis Artibus’. Over 300 white edge-pieces, along with similar pieces from red, blue and purple cylinders, suggest that the fragments are almost certainly refuse from a glazier's workshop. Medieval craftsmen did use such pieces on occasions. Glass was a costly commodity, far too precious to be tossed away indiscriminately after the modern fashion. However, the presence of such a high percentage of edge-pieces is significant. It is dramatically reinforced by a superb bull's eye in greenish-white glass. This shows that the glazier also bought in crown glass, made by the second process. This was produced by spinning the molten glass round on the end of an iron implement called a portal, so that by centrifugal force it became a circular, crown-shaped sheet of class, thicker in the centre or bull's eye, where it was attached to the pontil, than at the edge. This bull’s eye is the most impressive piece of glass in the collection. Measuring 155mm by 105mm, it increases from a thickness of 8mm at the edge to a solid 20mm at the centre, where a cross-shaped impression left by the pontil can clearly be seen. Such pieces were used during the Middle Ages for both domestic and ecclesiastical glazing, especially in Germany and Italy, but they are very rare in England. In post-medieval times they were popular here as a cheap form of domestic glazing, and are much in demand again with the present vogue of the pseudo-Georgian bow-window.

As far as we know, virtually no coloured glass was manufactured in England in the Middle Ages. It had to be imported from the Continent. White glass, however, was produced in several areas; the Weald area of Sussex and Surrey, with Chiddingfold as a major centre, was the most important, but a Shropshire-Staffordshire area was better placed to supply York, and we know that in 1417 the Minster authorities bought glass from a John Galsman, at Rugeley in Staffordshire. The Fabric Rolls of the Minster and the wills of the glaziers themselves show that most of the white glass used in York was of English origin (‘vitri Anglicani’), and that the coloured glass came mainly from the Rhineland areas of Hesse, Burgundy and Lorraine (‘Hass’ glas’, ‘vitri Borgandie’, and ‘Rennyshe’ are for example and referred to), and was brought into Hull or Bridlington by Hanse merchants and others. Some glass also came from the great glass producing area in Normandy, centred on the port of Rouen, (John Petty, in 1508, bequeathed white glass from Normandy to the Minster, as well as Rhenish glass to St Mary's Abbey). This area had considerable stylistic influence on York glasspainting. The two types of glass present in the City Garage find, may well reflect different areas of origin. We could perhaps attribute the muff produced white class to England and the coloured to the Rhineland, while the crown glass could be seen as the work of Normandy glassmakers, who seem to have been the major exponents of this technique. Chemical analysis will yield information on the constituent of the glass, and will enable us to make comparisons with glass in York and areas further afield.

Only eleven of the white fragments are painted. The paint is brown, usually consisting of copper or iron oxide mixed with molten glass and a binder; gumarabic, urine or wine. It should become firmly attached to the glass when fired in a kiln.

One piece, 30mm by 28mm (Fig 1), is part of a woman's head. Her right eye and eyebrow remain, with a kerchief with folds across the forehead and down the sides. The painting is very delicate, a very thin brush being used for the eyebrows and a thicker one for the outlines. The folds on the left side have been scratched through the paint with a needle to show white, and a wash has been applied to both sides of the glass to shade the kerchief. The head was designed for a figure panel with small-scale figures, and may even represent a donor. Another piece may be part of an animal, while a third looks like a drapery fragment.

The largest painted piece is a 'quarry', a diamond shaped pane, (Fig 2) 190mm by 55mm. It has a wavy-armed cross design, with trefoils between the arms and circular ornament in the centre. The trefoil and circles are stained yellow. This type of quarry is common in the fifteenth century in York and elsewhere. A similar type occurs as a background in the windows of the east aisles of the transepts in the Minster. These date from a reglazing of c.1433, when there are payments (recorded in the Fabric Rolls) for iron saddle bars to support two of the newly glazed windows. They seem to have been popular, however, to the end of the century. The quarry was no doubt rejected because of the inordinate thickness of 10mm at one end, which made it difficult to lead. Four other pieces look like quarry fragments. One, (Fig 3) shows contiguous quarries painted on the same piece of glass instead of being leaded separately.

Another piece, 35mm by 29mm, has circular ornament, a very common motif, often used in heraldry for example, to relieve the boredom of large areas of unpainted glass. (Fig 4)

Part of a fleur-de-lys as painted on one piece measuring 45mm by 35mm. Here the paint is used for a background on which the white fleur-de-lys is reserved. The edges of the piece are squared, so it was probably destined for a border, where such heraldic motifs were popular. (Fig 5)

Finally, one ruby piece (Fig 6) is painted, again with the ornament reserved on a painted ground. It may be a piece from a background.

Unfortunately there is insufficient detail to make a close dating on stylistic parallels with existing windows possible. A dating to the second half of the fifteenth century, probably the last quarter seems reasonable, and agrees with the date of the pottery found in the pit.

The raw-material nature of the glass, the meagerness of painted pieces (which in any case do not belong to the same window), and the absence of lead, all suggest that we are dealing with workshop rejects. The find was made in exactly that part of the city where, if any archaeological evidence of the medieval glasspainter survives, we would expect to find it. A few yards further down Blake Street and we are in Stonegate, which in medieval times stretched through the present St Helen's Square: this street, particularly the lower half around St Helen’s Church, was where the York glaziers lived and worked. Many of them were buried in the church, where there still survives in one of the windows a patched sixteenth century shield with the arms of their guild, showing the grozing-iron used to cut the glass before the introduction of the diamond. It seems that our glass dumped by someone working on the west side of the street, perhaps in his backyard, where he no doubt had a small kiln at a safe distance from his house. Amongst those buried in St Helen’s, in the second half of the fifteenth century, were members of the Inglish, Petty and Preston families who dominated the York glasspaanting scene at this period.

As far as I am aware, a find of this type is unique in this country. With the present opportunities for excavation in the centre of the city, one can hope for further discoveries of this nature, as well as glass from churches and houses. This will help to widen our knowledge of an art form, which places such an important part in the life of the medieval city, and still today attracts worshippers, artlovers and tourists from all over the world. Who knows, perhaps, one day Wilfrid’s glass may yet see the light of day again!

David O’Connor

David O’Connor is Radcliffe Research Fellow in Medieval Stained Glass Studies in the Centre for Medieval Studies, University of York.

Further Reading:

J.A. Knowles, ‘The York School of Glass-Painting’ (1936).

L.F. Salzman, ‘Building in England down to 1540’ (1952).