In architecture, Tracery is the stonework elements that support the glass in a Gothic window. The term probably derives from the 'tracing floors' on which the complex patterns of late Gothic windows were laid out.

Plate tracery

The earliest form of window tracery, typical of Gothic architecture prior to 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 1140's, the pointed-arch Gothic window (employed by Abbot Suger
Abbot Suger
Suger was one of the last Frankish abbot-statesmen, an historian, and the influential first patron of Gothic architecture....

 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
Lancet window
A lancet window is a tall narrow window with a pointed arch at its top. It acquired the "lancet" name from its resemblance to a lance. Instances of this architectural motif are most often found in Gothic and ecclesiastical structures, where they are often placed singly or in pairs.The motif first...

 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
Trefoil is a graphic form composed of the outline of three overlapping rings used in architecture and Christian symbolism...

 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
Soissons Cathedral
Soissons Cathedral is a Gothic cathedral in Soissons, France. The construction of the south transept was begun about 1177, and the lowest courses of the choir in 1182. The choir with its original three-storey elevation and extremely tall clerestory was completed in 1211...

, right). With this type of design, the spandrel
A spandrel, less often spandril or splaundrel, is the space between two arches or between an arch and a rectangular enclosure....

s (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 trefoil
Trefoil is a graphic form composed of the outline of three overlapping rings used in architecture and Christian symbolism...

s, quatrefoil
The word quatrefoil etymologically means "four leaves", and applies to general four-lobed shapes in various contexts.-In heraldry:In heraldic terminology, a quatrefoil is a representation of a flower with four petals, or a leaf with four leaflets . It is sometimes shown "slipped", i.e. with an...

s and oculi used to fill the spaces above them.

The rose window
Rose window
A Rose window is often used as a generic term applied to a circular window, but is especially used for those found in churches of the Gothic architectural style and being divided into segments by stone mullions and tracery...

s of early- and high-Gothic cathedrals, such as the example in the north transept
For the periodical go to The Transept.A transept is a transverse section, of any building, which lies across the main body of the building. In Christian churches, a transept is an area set crosswise to the nave in a cruciform building in Romanesque and Gothic Christian church architecture...

 of Laon Cathedral (1170's) 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.

A common image used by art historians to help visualise the distinctive characteristics of plate tracery is to imagine rolling out a flat sheet of cookie-dough, then punching holes in it with a limited set of shaped cookie cutters. (In practice of course, windows were not cut out of continuous sheets of stone - plate tracery was constructed from carefully shaped and jointed pieces of masonry which were coursed in to the surrounding walls - but the analogy is still a helpful one).

Bar tracery

To continue the cookie-dough metaphor, bar-tracery is what would result from rolling thin flexible coils of dough with one's hands and then bending and joining them into complex, interlacing patterns.
The earliest bar tracery designs were made for the aisle windows at Reims 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 mullion
A mullion is a vertical structural element which divides adjacent window units. The primary purpose of the mullion is as a structural support to an arch or lintel above the window opening. Its secondary purpose may be as a rigid support to the glazing of the window...

s 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, left, 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
Armature may refer to:* Armature , the kinematic chains used in computer animation to simulate the motions of virtual characters...

) 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
Lime mortar
Lime mortar is a type of mortar composed of lime and an aggregate such as sand, mixed with water. It is one of the oldest known types of mortar, dating back to the 4th century BC and widely used in Ancient Rome and Greece, when it largely replaced the clay and gypsum mortars common to Ancient...

 to set. The technical aspects of the windows at Reims clearly fascinated Villard de Honnecourt
Villard de Honnecourt
Villard de Honnecourt was a 13th-century artist from Picardy in northern France. He is known to history only through a surviving portfolio of 33 sheets of parchment containing about 250 drawings dating from the 1220s/1240s, now in the Bibliothèque Nationale, Paris...

, who visited the construction site, probably in the 1220's, 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).

Blind and open tracery

As bar tracery opened the way for more complex patterns, masons started applying those same patterns to other surfaces as well as the actual window openings. When used on an otherwise solid walls, such motifs are known as blind tracery, a decorative effect first applied on the west facade of the church of St Nicaise at Reims (1230's). Conversely, tracery was also constructed as openwork screens, which could either match the window tracery behind them (e.g. the Basilica of Saint Urbain, Troyes) or create a visual counterpoint to it, as on the exterior of the west facade of Strasbourg Cathedral
Strasbourg Cathedral
Strasbourg Cathedral or the Cathedral of Our Lady of Strasbourg is a Roman Catholic cathedral in Strasbourg, France. Although considerable parts of it are still in Romanesque architecture, it is widely consideredSusan Bernstein: , The Johns Hopkins University Press to be among the finest...

. Open tracery in particular was a key feature of the later phases of Rayonnant
Rayonnant is a term used to describe a period in the development of French Gothic architecture, ca. 1240–1350. Developing out of the High Gothic style, Rayonnant is characterised by a shift in focus away from the great scale and spatial rationalism of buildings like Chartres Cathedral or the...


Islamic Influence

One of the characteristics of tracery found in gothic architecture is the use of multilobed arches and complex compound arches set atop columns. This is but one example of the influence of Islamic forms of architecture in the development of gothic tracery. As the Reconquista
The Reconquista was a period of almost 800 years in the Middle Ages during which several Christian kingdoms succeeded in retaking the Muslim-controlled areas of the Iberian Peninsula broadly known as Al-Andalus...

 spread throughout Spain, many Mosques and Fortresses were converted into Churches and Christian Castles. It is from this pattern of conversion that many elements of Islamic architecture were incorporated into Gothic Christian Architecture. The most notable example of this can be seen in the Great Mosque of Cordoba
The Cathedral and former Great Mosque of Córdoba, in ecclesiastical terms the Catedral de Nuestra Señora de la Asunción , and known by the inhabitants of Córdoba as the Mezquita-Catedral , is today a World Heritage Site and the cathedral of the Diocese of Córdoba...

, which features complex tiers of compound arches in an almost fractal arrangement. This characteristic of Andalusian
Al-Andalus was the Arabic name given to a nation and territorial region also commonly referred to as Moorish Iberia. The name describes parts of the Iberian Peninsula and Septimania governed by Muslims , at various times in the period between 711 and 1492, although the territorial boundaries...

 architecture would become more complex in later periods and be combined with intricate stucco work to produce blind and openwork tracery on many Islamic monuments in Spain.

Tracery patterns and the phases of Gothic

Most 19th century histories of Gothic architectural style used a series of rather arbitrary categories based on the supposed evolution of the dominant patterns of window tracery. Such teleological
A teleology is any philosophical account which holds that final causes exist in nature, meaning that design and purpose analogous to that found in human actions are inherent also in the rest of nature. The word comes from the Greek τέλος, telos; root: τελε-, "end, purpose...

 models are now regarded as oversimplistic and are generally shunned by art historians, though they live on in the popular literature. In terms of the overall development of Gothic architecture, the crucial development was not so much the use of any particular tracery patterns but the transition from plate- to bar-tracery, which was what made the Rayonnant
Rayonnant is a term used to describe a period in the development of French Gothic architecture, ca. 1240–1350. Developing out of the High Gothic style, Rayonnant is characterised by a shift in focus away from the great scale and spatial rationalism of buildings like Chartres Cathedral or the...

 and subsequent styles possible.

Tracing floors and épures

As the complexity of tracery increased, so did the need for masons to draw out their designs in advance, either as a way of experimenting with patterns or as a way of communicating their designs to other craftsmen or to their patrons. Because of the cost and size limitations of parchment sheets, such designs would normally be drawn by incising onto a whitewashed board or a conveniently placed section of flat wall. In the latter case, the wall would be prepared with a thin layer of plaster, which would show the design more clearly. A number of churches and cathedrals still show the faint remains of these tracings (or épures as they are known in France), from where the mason's compass points scratched through the plaster and into the masonry below. (Examples include some experimental 14th century window tracery patterns at the eastern end of the south wall inside the Galillee porch of Ely Cathedral
Ely Cathedral
Ely Cathedral is the principal church of the Diocese of Ely, in Cambridgeshire, England, and is the seat of the Bishop of Ely and a suffragan bishop, the Bishop of Huntingdon...

, or the extensive series of tracings on the flat aisle roofs of Clermont-Ferrand Cathedral.)
A number of major building sites (including Westminster Abbey
Westminster Abbey
The Collegiate Church of St Peter at Westminster, popularly known as Westminster Abbey, is a large, mainly Gothic church, in the City of Westminster, London, United Kingdom, located just to the west of the Palace of Westminster. It is the traditional place of coronation and burial site for English,...

, Wells Cathedral
Wells Cathedral
Wells Cathedral is a Church of England cathedral in Wells, Somerset, England. It is the seat of the Bishop of Bath and Wells, who lives at the adjacent Bishop's Palace....

 and York Minster
York Minster
York Minster is a Gothic cathedral in York, England and is one of the largest of its kind in Northern Europe alongside Cologne Cathedral. The minster is the seat of the Archbishop of York, the second-highest office of the Church of England, and is the cathedral for the Diocese of York; it is run by...

) originally had dedicated tracery chambers, where the architects could prepare their designs in relative comfort. The availability of a large flat floor surface meant that designs could be drawn life-size and the individual elements of bar tracery laid out on the plan to test their goodness of fit, before hoisting them up the scaffolding for installation in the actual window openings. This also meant that masons could carry on working through the winter season, when building work would normally grind to a halt.
The tracing floors themselves were covered with plaster of paris, which could be relaid and smoothed down after each set of designs were finished with. The 14th century tracing house at York (also known as the Mason's Loft) survives to this day on the upper storey of the corridor leading to the Chapter House
Chapter house
A chapter house or chapterhouse is a building or room attached to a cathedral or collegiate church in which meetings are held. They can also be found in medieval monasteries....

; the complex web of lines and curves scratched into the floor serving as witnesses to the countless different designs that were worked out in there. The high-quality carpentry and the inclusion of a garderobe
The term garderobe describes a place where clothes and other items are stored, and also a medieval toilet. In European public places, a garderobe denotes the cloakroom, wardrobe, alcove or an armoire. In Danish, Dutch, German and Spanish garderobe can mean a cloakroom. In Latvian it means checkroom...

and fireplace in the York tracing house also give an indication of the rising status of the architect around the 14th century.
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