Tracery is an architectural device by which windows (or screens, panels, and vaults) are divided into sections of various proportions by stone bars or ribs of moulding. Most commonly, it refers to the stonework elements that support the glass in a window. The purpose of the device is practical as well as decorative, because the increasingly large windows of Gothic buildings needed maximum support against the wind. The term probably derives from the tracing floors on which the complex patterns of windows were laid out in late Gothic architecture. Tracery can be found on the exterior of buildings as well as the interior.
There are two main types: plate tracery and the later bar tracery.Honour, H. and J. Fleming, (2009) A World History of Art. 7th edn. London: Laurence King Publishing, p. 948. The evolving style from Romanesque to Gothic architecture and changing features, such as the thinning of lateral walls and enlarging of windows, led to the innovation of tracery. The earliest form of tracery, called plate tracery, began as openings that were pierced from a stone slab. Bar tracery was then implemented, having derived from the plate tracery. However, instead of a slab, the windows were defined by moulded stone mullions, which were lighter and allowed for more openings and intricate designs.Hamlin, Alfred (1906). A text-book of the history of architecture (7 ed.). New York, Longmans. pp. 188.
Pointed arch windows of Gothic buildings were initially (late 12th–late 13th centuries) lancet windows, a solution typical of the Early Gothic and of the Early English Gothic. Plate tracery was the first type of tracery to be developed, emerging in the style called High Gothic. High Gothic is distinguished by the appearance of bar tracery, allowing the construction of much larger window openings, and the development of curvilinear tracery, ultimately contributing to the Flamboyant style. Late Gothic in most of Europe saw tracery patterns resembling lace develop, while in England Perpendicular Gothic preferred plainer vertical mullions and transoms.
Plate tracery
Plate tracery, in which lights were pierced in a thin wall of ashlar, allowed a window arch to have more than one light – typically two side by side and separated by flat stone spandrels. The spandrels were then sculpted into figures like a roundel or a quatrefoil. Plate tracery reached the height of its sophistication with the 12th-century windows of Chartres Cathedral and in the "Dean's Eye" rose window at Lincoln Cathedral.
The earliest form of window tracery, typical of Gothic architecture before the early 13th century, is known as plate tracery because the individual lights (the glazed openings in the window) have the appearance of being cut out of a flat plate of masonry. Romanesque church windows were normally quite small, somewhat taller than wide and with a simple round-headed ('segmental') arch at the top. From around the 1140s, the pointed arch Gothic window (employed by Abbot Suger for the redesign of the choir at St Denis) started to take over.
As the buttressing systems of early Gothic architecture reduced the structural need for broad expanses of thick walls, window openings grew progressively larger and instead of having just one very large window per bay division (which would create problems with supporting the glass), the typical early-Gothic 'twin lancet plus oculus' form of plate tracery developed. This consists of two (sometimes three) tall thin lights topped with pointed arches, with a round or trefoil opening placed above them, often contained within a blind arch which gives the whole assemblage a pointed lancet shape (see the example from Soissons Cathedral). With this type of design, the spandrels (i.e. the spaces between the tops of the lancet windows and the oculus) are just blank wall. The practicalities of building window tracery in this way severely limited the complexity of designs that could be produced and although plate tracery designs evolved over the course of the 12th and early 13th centuries, in practice, the only real variation was in the number and size of lancets and in the trefoils, quatrefoils and oculi used to fill the spaces above them.
The rose windows of early- and high-Gothic cathedrals, such as the example in the north transept of Laon Cathedral (1170s) or the west facade at Chartres (c. 1210), also employed plate tracery. This greatly limited the overall amount of light admitted to the interior by these windows, as well as restricting the complexity of patterns that could be created.
Bar tracery
At the beginning of the 13th century, plate tracery was superseded by bar tracery. Bar tracery divides the large lights from one another with moulded mullions. Bar tracery, an important decorative element of Gothic styles, appeared first at Reims and was employed in England around 1240. After 1220, master builders in England had begun to treat the window openings as a series of openings divided by thin stone bars, while before 1230 the apse chapels of Reims Cathedral were decorated with bar tracery with cusped circles (with bars radiating from the centre). Bar tracery became common after c. 1240, with increasing complexity and decreasing weight. The lines of the mullions continued beyond the tops of the window lights and subdivided the open spandrels above the lights into a variety of decorative shapes. Rayonnant style (c. 1230–c. 1350) was enabled by the development of bar tracery in Continental Europe and is named for the radiation of lights around a central point in circular rose windows. Rayonnant also deployed mouldings of two different types in tracery, where earlier styles had used moulding of a single size, with different sizes of mullions. The rose windows of Notre-Dame de Paris (c. 1270) are typical.
The earliest bar tracery designs were made for the aisle windows at Reims Cathedral around 1215. The Reims windows still used the same 'two lancets plus oculus' pattern (as in the Soissons example above), but now the glass panels were held between narrow stone mullions made up of carefully shaped lengths of masonry (fitted together with mortar and metal pins) quite distinct from the wall surrounding them. These mullions were much more slender than the corresponding elements in plate-tracery windows and crucially, the previously solid wall areas such as the spandrels could also now be glazed, greatly increasing the amount of light admitted.
The cross-section of each mullion or tracery bar was important both for the structural integrity of the window and for the visual effect. As can be seen in Viollet-le-Duc's diagram (right) there was normally a roll-moulding on both the inside and outside of the windows, which made the mullions appear even more slender than they actually were. The shoulder marked 'B' on the diagram is the glazing slot, into which the metal frame (armature) of the window glass is mounted. Unlike with plate tracery, where each stone had to be individually shaped, the elements of bar tracery could be mass-produced to standard templates in the mason's yard – work that could continue even when it was too cold for lime mortar to set. The technical aspects of the windows at Reims clearly fascinated Villard de Honnecourt, who visited the construction site, probably in the 1220s, and made a detailed sketch of the various templates, using a key to show how they fitted into the different parts of the window (the templates are in the lower half of folio 32 recto; the symbols besides the templates match similar ones on the detailed drawing of the Reims elevations on the facing page, folio 31 verso).
French Gothic
Rayonnant Gothic
Rayonnant is the term used particularly to describe the style that produced the great rose windows of France. These windows deck not only the west fronts of churches, but often, as at Notre-Dame de Paris, the transept gables as well. It is common that although the transepts of French churches do not project strongly, they are given visual importance almost equal to the west front, including large decorated portals and a rose window. Particularly fine examples are at Notre-Dame and Chartres Cathedral.
Flamboyant Gothic
The ogee arch is drafted from four points, creating a flame-like S-shaped curve. These arches create a rich and lively effect when used for window tracery and surface decoration. The form is structurally weak and has very rarely been used for large openings except when contained within a larger and more stable arch.
Some of the most beautiful and famous traceried windows of Europe employ this type of tracery. It can be seen at St Stephen's Vienna, Sainte-Chapelle in Paris, at the Cathedrals of Limoges and Rouen in France. In German and Spanish Gothic architecture, it often appears as openwork screens on the exterior of buildings. The style was used to rich and sometimes extraordinary effect in both these countries, notably on the famous pulpit in Vienna Cathedral.
English Gothic
Geometrical tracery
The early phase of the Decorated style (late 13th century) is characterized by Geometrical tracery – simple bar tracery forming patterns of foiled arches and circles interspersed with triangular lights. The mullions of Geometrical style typically had capitals with curved bars emerging from them. Intersecting bar tracery (c. 1300) deployed mullions without capitals which branched off equidistant to the window-head. The window-heads themselves were formed of equal curves forming a pointed arch and the tracery bars were curved by drawing curves with differing radii from the same centres as the window-heads. The mullions were in consequence branched into Y-shaped designs further ornamented with cusps. The intersecting branches produced an array of lozenge-shaped lights in between numerous lancet arched lights. Y-tracery was often employed in two-light windows c. 1300.
Geometrical tracery is identified by the circular openings at the head of the arch of the window. A common composition is three lights beneath two circles and a third at the point of the arch; such an example can be seen along the aisle at Lincoln Cathedral Also at Lincoln Cathedral, the east window is an expanded version of this idea with two interior arches, a total of eight lower lights, four small circular lights topped with two larger circles to fill out the interior arches, and finally above all one large circular shape filled with seven smaller circular lights. Geometrical tracery, in its early stages, had a rule of equilateral law, where the tracery design follows the shape of the arch in an equilateral manner. Additional decorative elements can be implemented, such as foliation or the "spherical triangle". The use of spherical triangles is a later adaption, derived from Westminster Abbey, and likely reflects religious significance.
The equilateral arch lends itself to filling with tracery of simple equilateral, circular and semi-circular forms. In France, windows of clerestories and other larger windows were commonly divided into two lights, with some simple Geometric tracery above, a circle or a cinquefoil or sexfoil. This style of window remained popular without great change until after 1300.
In England there was a much greater variation in the design of tracery that evolved to fill these spaces. The style is known as Geometric Decorated Gothic and can be seen to splendid effect at many English cathedrals and major churches, where both the eastern and the western terminations of the building may be occupied by a single large window such as the east window at Lincoln. Windows of complex design and of three or more lights or vertical sections are often designed by overlapping two or more equilateral arches springing from the vertical mullions.
Curvilinear (flowing) tracery