stained glass - development and techniques, also rose windows

related page:
gothic cathedral and church construction

this page is currently being developed

stained glass development

• Earliest from 10th century (900 - 999), but none has survived.
• 12th to 13th century (1100 -1299) - superimposed medallions
  intense brilliant blues and red thick glass and leading smoothed down with a plane
  Cistercians favoured grisaille windows
• 14th to 15th century (1300 - 1499) - the leading was no longer handmade so not so less heavy, the glass thinner, enabling larger windows to be made. Gothic canopies were put over human figures.
• 16th century (1500 - 1599) - delicately coloured pictures in thick lead frames, often copied from pictures, with great attention to detail and perspective
• 17th,18th,19th century (1600 - 1899) - traditional leaded stained glass often replaced by vitrified enamel or painted glass
• 20th century (1900 - 1999) - the necessity of restoring or replacing very old stained glass led to both a return to the original skills and styles, and to modern works, generally done with greater imagination that the previous three or four centuries.

rose windows - cathedral window styles

In medieval christianism, paganism was still prevalent; and there was also an excitement with a mysticism of numbers that reached right back to Pythagoras. The construction of the gothic cathedrals and their windows involved very complex geometries, with on-going challenges to gain stable structures within the circle.

Perpetual motion machine, drawn by Villard de Honnecourt, c.1225 - 1250	A cartwheel Original image credit: LeoL30

Wheels were, of course, technology: wheels for carts that worked, water wheels, mill wheels, wheels for raising heavy loads, treadmills for providing power, the spread of windmills. This was exciting, a new world was developing. Little detail has come down to us, surviving the intervening eight hundred years or so. One of the great treasures that has survived is the design notebook of Villard de Honnecourt. Who knows, perhaps we can even dream of a perpetual motion machine powering this revolution? Or the devil may be confused by a circular maze on the floor, as can be seen just inside the entrance at Chartres cathedral.

Eight hundred years later, we must gain clues wherever we may: an illuminated letter in a manuscript, a quick builder’s sketch on the stones underneath the eaves, and most of all from examining the buildings.

In a rough chronology:

• Simple oculus: a round hole in the wall
• Romanesque - wheel
• Romanesque/Gothic transition - Beauvais - wheel of fortune, which depicts humans being drawn up one side of the wheel to increasing good fortune, only to be plunged down the other side in despair. Also Saint Denis, Sens, Senlis, Noyon
• Gothic Rose - Mantes, Laon, Chartres, Paris
• Snow crystal - Sees
• Flamboyant (flames) - Amiens, Sens, Troyes, Auxerre, Sainte-Chapelle (Paris), Beauvais

As the mastery of gothic architecture proceeded, and great areas opened up to the potential for being glazed, shapes developed naturally to fill the appropriate spaces. The circle fitted naturally into the leaping arches, as did lancets into narrower, pointed openings.

These times were the true renaissance of Northern Europe, with new techniques, burgeoning populations supported by the development of deep ploughing on the rich soils of the North, and growing knowledge.

wheels within wheels

West rose window (exterior) at Orvieto cathedral,
mid-14th century [say 1350]

Circular windows have a tendency to rotate under the slightest asymmetric pressure. The circle has to be maintained with spokes of a wheel and arches. The outside of the circle is, of course, one continuous arch. All these great buildings, as they developed, were experimental. The centre of the West Rose at Chartres is still, to this day, off-centre by about a foot (30 cm), while the transept roses at Notre-Dame de Paris had to be taken down and redesigned.

There is a war between making the window as solid as possible and maximising the glass area, a war between the simple shape and the complexity of the work of art. Let us make circles within circles, as with the glorious Chartres’ west rose. How about some squares, as with Chartres’ north? Elsewhere can be found triangles and pentagons [Laon west rose], some of the most stable of shapes; or perhaps hexagons would be used, or any other shape that took their fancy.

Over the next century or two, as the experience of the builders increased, the tracery became more decorative and imaginative. The obvious wheels gave way to the more seemingly organic lines of the flamboyant windows, such as those at Amiens, Sens and Troyes. These are windows with sweeping spirals and ‘paisley’ shapes. Tours has a lozenge rose; and then there is my very special snowflake window at Sees. Below the rose windows was usually a parade of lancets, and often a new moon as a tiara filling the space above.

By the mid-fourteenth century [say 1350], the flamboyant style was fully developed. The name flamboyant came from the fiery shapes of the stone tracery, often also blazing with colour. In such windows, all straight lines were eliminated, leaving curving, curling flames. These roses were never to reach the grand scale of the great gothic roses. The more intricate stonework of flamboyant rose windows demanded only the hardest, most consistent stone, which alone could manage the stresses, even if achieving less ambitious sizes.

In the fifteenth to sixteenth centuries [1400 to 1599], buildings that had been started centuries earlier were completed with the latest style of stained glass window - the flamboyant.

so now for a bit on glass

glass making methods

• At first, in the earlier part twelfth century [1100-1199] and before, glass was cast and the ingredients added at significant instants during the melting process. The result was called ‘pot-metal’.
• As the twelfth century progressed, glass was blown so to give a much thinner product that was easier to handle. This‘muff’ glass was blown into a long cylinder shape. This was then cut open and flattened into a sheet. Using a red-hot crozing-iron, the sheet was cut up and the pieces of glass selected for their position in the final composition.

glass ingredients

• Generally, to make the glass, two parts of beechwood (or fern) ash were combined with one part of river sand, the furnace heat fusing the mixture into a slightly purple-coloured mass (the colour being due to manganese impurities).
• Metallic compounds were added during fusion to give the required colour:
  • cobalt oxide (from Bohemia) made blue
• copper oxide made red
• silver chloride made yellow.

technique - glass to window

• The design was drawn onto a whitewashed table.
• Pieces of glass were cut and selected so that internal flaws were well exploited. The f1aws - such as bubbles, grits of sand, streaks and variations in thickness - all refract the light as it passes through the glass. This causes the glass sparkle and sing.
• Some of the glass was shaped and immediately fitted into the window.
• A much greater proportion received further treatment with pigment made from a mix of iron filings and resin. This brought out highlights, shadows, lines and other details. The pigment was painted on to the glass to create various details before being fired.
• A technique called flashing was used to make particular colours and effects.
  With flashing, a thin layer of one glass was pasted onto another differently coloured piece, the ensemble then being fired to fuse the glasses together.
  The main glass receiving this technique was the dark, ruby red glass. By building up as many as twenty or thirty thin layers of red glass onto a clear base, fired after layer added, a rich but not dark red colour was achieved. This method allowed layers to be ground off to give varying tones within the glass. Further colours could be made by staining, rarely done in medieval times.

from medieval glass to dalle de verre, or slab glass

In medieval times, the manufacture of stained glass was an esoteric craft involving glass-blowing. The quality of the glass varied greatly, in consistency, thickness and so on. The surface varied, bubbles of air were trapped in the glass, the colour varied, and since those days, acids in the air and rain, and from pollution, pitted the outside surfaces over the centuries. This can be seen in the whitening of the surfaces.

You may think that all this variation is a problem, but far from it. These variations are a good part of what gives old windows such character, sparkle and glow. In fact, restorations over the past century have often done more harm then good, as some of the life has been removed from the windows. However, as knowledge grows, restorers are now often doing a better job.

Eventually, the old handcrafts involved in glass manufacture were replaced by metal molding and glass flotation. The product became consistent, most of the bubbles were removed, the surface became smooth and the colour evenly distributed. This ended up in a product lifeless from the point of view of the finished window. This product became known, in a monumental misnomer, as ‘cathedral glass’!

So the glass makers have had to learn all over again how to produce a more appropriate material and result. As modern science catches up with medieval craftsmen, the palette of the stained glass artists is now becoming good enough even to incite the envy of a 12th century monk.

Added to the range of glass available, there is now a great modern innovation dalle de verre, or slab glass. This material has opened up the possibility of embedding the inch-thick glass in concrete or resin. As glass expands at approximately the same rate as the concrete, these windows can be made to be structural, as well as damned impressive.

To add still further to the lively colour and light transmission qualities of this glass, the craftsman deliberately chips the inside surface of the glass, with a hammer, as can be seen in the photo just below.

The stained glass shown here comes from the church of Notre-Dame-de-la-Mer, at La Cotinière on the Île d’Oleron

great contemporary stained glass artists

Unfortunately, great stained glass artists are few and far between. The best I know is Gabriel Loire, who has unfortunately died recently at a great age. The best example of his work in England is at St Mary’s College Chapel, Strawberry Hill, near Twickenham, using dalle de verre. His son Jacques, and I believe his grandchildren, are now involved in the business, which has a shop next door to Chartres cathedral. However, his descendants are not yet in the same class as Gabriel.

There is a prime example, in a single window, of Chagall’s work at Chichester cathedral. He has also glazed a complete church of 12 windows at Tudeley, Kent. But his definitive tour de force is at the 12 magnificent windows at the chapel of the Hadassa Hospital, a little way out of Jerusalem. There are also several windows in Metz cathedral, but these I have not seen.

Matisse has created an impressive chapel at Vence in Provence, designing practically everything within it, including the stained glass windows. (Its visiting hours are limited, so check carefully before visiting.)

See below for a very useful catalogue of stained glass in Britain.

recommended books

The rose window, splendour and symbol by Painton Cowen Thames and Hudson [UK], hbk, 2005 276 pages, 350 illustrations, 300 in colour ISBN-10: 0500511748 ISBN-13: 978-0500511749 £29.99 [amazon.co.uk] $63.75 [amazon.com] Previously, Painton Cowen also wrote Rose windows (Art & Imagination) pbk, 1990 ISBN-10: 0500810214 ISBN-13: 978-0500810217 amazon.com / amazon.co.uk

Extremely well illustrated - the paperback version has 59 in colour and 82 black-and-white, while I see that the new hardback version has 300 colour and 50 b/w - I will report further when I have received a copy. Densely packed with facts. An ideal primer to be carried around with you on any visit. Like so many books, written by informed hands, it is very badly organised and laid out. My Thames and Hudson glued paper-cover version started falling apart from early on, but always travels in its own protective plastic cover to keep the pages in one place. I can not resist giving this book five GoldenYaks, if only because I know of nothing better.

Painton Cowen has also produced a very useful directory of stained glass in Britain -

A guide to stained glass in Britain by Painton Cowen, # Michael Joseph Ltd (June 10, 1985) ISBN-10: 0718125673 ISBN-13: 978-0718125677 amazon.com / amazon.co.uk

Experiments in gothic structure by Robert Mark MIT Press pbk 0262630958 reprint: 1984 amazon.com / amazon.co.uk

If you want to understand the structure of the great gothic cathedrals, this is the place to go. Some of it gets a bit technical, Mark used polarised light, epoxy plastic models and wind tunnels to work out the the loadings and stresses in some of the great cathedrals. An absolutely fascinating book to read, if you can stand the hard work and the usual technical manual disorganisation.

As with Painton, I can not resist giving this book five GoldenYaks, if only because I know of nothing better.

end notes

1. A good start on architecture can be found in the introduction to the Michelin Green Guide series.
   
   
2. Naturally, the greater the magnification of your binoculars, the greater the problem with handshake. The greater the magnification, also the more bulk and weight to carry around. Choosing a pair of binoculars to suit you is, therefore, a compromise. The small cheap ones can vary a great deal in quality - try them out before buying.
   
   
3. Halation

   Light spilling from one section of glass to another. However, these old craftsmen knew their trade, thus thickening the leading where this is most likely to occur. They even could take foreshortening into account.
   

4. Reims, like everything on the German side of the World War One German front, lost a great deal of its treasure, including glass, to German shelling. The Germans used the cathedrals and churches in the area for target practice. Hence, all the great stained-glass treasures of France are to the west of that line.
   
   The philistines of the French Revolution also did a great deal of damage to French heritage (as mentioned regarding Saint Denis above), as Cromwell did in England.
   
   The third era of destruction across northern France was occasioned in driving the National Socialists out of France in 1944 in association with the D-Day landings.
   
   
5. Lancet

   pointed, as seen in the arches and windows with a pointed head introduced in the Gothic period of architecture. [From the point of a lance - a spear.]
   
   

6. Medallion

   In stained glass, a medallion refers variously to a circular; oval, square or diamond shaped space, generally one of many within the overall window design, that contains a figure or figures.
   Yoked medallions are two medallions partially joined together.
   
   

7. Grisaille

   Almost monochrome glass, each piece shaped as a square or diamond and painted with black enamel paint. From a distance, grisaille windows have an overall greyish tint; hence the name grisaille, meaning greyness in French.
   
   

8. Being more precise, and quoting from Mark [primarily form p.115], “The Bourges sexpartite vault is estimated to weigh 370,000 kg (820,000 lb), that is approximately 400 imperial tons. Whereas, Mark estimates that the Cologne quadripartites to weigh 270,000 kg (600,000 lb), that is going on 300 imperial tons. [An imperial ton is 2440 lb, while a short or American ton is 2000lb.]
   
   The vaults also have rubble, or fill, to increase pressure and to help stablise them. This included in the weights quoted. Mark estimates that the horizontal outward thrust on the main piers as 28,100 kg (62,000 lb) at Bourges, and 31,300 kg (69,000 lb) at Cologne. The secondary, lighter pier at Bourges, Mark estimates at 11,300 kg (25,000 lb). This gives some comparison of the gains attained by the Bourges sexpartite vault construction.

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cathedrals – introduction: reading stained glass
gothic cathedral and church construction
cathedrals 1: Rouen and Monet
cathedrals 2: Dax and church iconography
cathedrals 2: photographs, Dax
cathedrals 3: Poitiers, neglected masterpiece
cathedrals 3: photographs, Poitiers / photos 2
cathedrals 4: Angers, heart of the Angevin Empire
cathedrals 4: photographs, Angers

cathedrals 5: Laon, the midst of the gothic transition, with added oxen
cathedrals 5: photographs, Laon
cathedrals 6: Saint-Jean-Baptiste de Lyon
cathedrals 7: Notre Dame of Lausanne
Lausanne rose window - photo-analysis
Cambrai cathedral
Soissons Cathedral
Germans in France - Arras cathedral
Germans in France - Reims cathedral
Germans in France - St. Quentin cathedral

email abelard@abelard.org

© abelard, 2006, 23 february


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the address for this document is http://www.abelard.org/france/cathedral_stained_glass.php

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