Traceries

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. There are two main types, plate tracery and the later bar 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 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, right). 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 (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.

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