Basic Elements of a Gothic Window
Vertical lines of stonework within a window, are called
mullions. These divide the window into compartments called lights.
So, for example, three mullions will produce a 4-light window.
Stone tracery fills the upper part of the window. As well as
providing the main decorative features, the mullions and tracery
divide the window into smaller units to carry the leaded panels of
glass.
The name geometrical is an appropriate description for this
early type of tracery because all the constructions of the window
patterns are achieved using only a pair of compasses. Hence all the
outline shapes in the tracery consist of circles or parts (arcs) of
circles.
To introduce some decoration into a plain circular opening, foil
patterns are inserted. These resemble leaves or petals and are
created by joining several part-circles together.
In larger windows cinquefoil, sexfoil, or octofoil patterns,
with 5, 6 or 8 leaves respectively, may be found.