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.
There are two main types: plate tracery and the later bar tracery. 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.
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.
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
thumb|Geometrical tracery in the east window of Lincoln Cathedral
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. 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
thumb|Decorated bar tracery, [[All Saints Church, Lindfield, east window. A row of soufflets at the bottom, with mouchettes above and another soufflet at the top.]]thumb|Curvilinear bar tracery, [[Cottingham, East Riding of Yorkshire, parish church|alt=]]
Second Pointed (14th century) saw Intersecting tracery elaborated with ogees, creating a complex reticular (net-like) design known as Reticulated tracery.
Perpendicular
thumb|Perpendicular bar tracery, [[King's College Chapel, Cambridge, great east window]]Perpendicular Gothic developed in England from the mid-14th century and is typified by Rectilinear tracery (panel-tracery). Panel tracery was more common in the east, and alternate in the south-west. Both types could be elaborated with larger arch patterns, termed subarcuation, as at King's College Chapel, Cambridge, York Minster, Beverley Minster and Cartmel Priory. Four-centred arches were used in the 15th and 16th centuries to create windows of increasing size with flatter window-heads, often filling the entire wall of the bay between each buttress.
Rounded quatrefoils
In Gothic tracery, rounded quatrefoils have been used in modern industrial ornament which is used to embellish different parts of a building or certain objects. This is formed with the use of squares as the base and then constructing circles tangent to each side of the square in the center of the side as well as a tangent to each of the circle's sides. This type of construction is used generously in Gothic buildings.