Tracery is a form of architectural decoration in which a frame (often a window, railing, or blind arch) is filled with interlacing bands of material. (A "blind arch" is an arch-shaped depression in a wall; tracery that spans a blind arch is known as "blind tracery".) Tracery of exceptional refinement is found in Islamic architecture (see Islamic Art) and Gothic architecture.
Pointed Arches and Foils
The two principal motifs of Gothic tracery are the pointed arch and foil. A "foil" is a clover-like shape that features three or more "leaves"; the most common types are the trefoil (three-leaf) and quatrefoil (four-leaf), though Gothic architects freely added any number of additional foils.
A typical Gothic window can be divided into two sections. The lower section features two or more adjacent pointed arches, which may themselves be subdivided. The remaining space in the upper section of the window is often filled with a foil enclosed in a circle, or some variation thereof.
A partial foil nestled under the point of an arch results in a foil arch. The tips of foil leaves may also be embellished in this manner.
Petals, another common motif in Gothic tracery, are a standard feature of the rose window, a great circular window found above the main entrance of many cathedrals.
One often encounters a spade-like shape in Gothic tracery; this occurs when the leaf of a foil stretches into a corner.
One subtype of Gothic tracery is flame tracery, which features an abundance of sharp curves and points. Flame tracery was a development of the Late Gothic period, during which architects pushed Gothic elaboration to incredible extremes.