Construction Design Mathematics: a Gothic window with intersecting or Y-shaped tracery

This is a lesson suitable when students have mastered the lancet window (see relevant lesson plan).

Intersecting tracery

Where a dripstone is placed around the outer arcs of the two lancet lights, the area above the lights lends itself to the sculpted opening of a natural rhombus or lozenge type shape, formed with concave sides below, and convex above. This makes for a very elegant window that can be seen on many churches.

The overall design is termed intersecting or Y-shaped tracery and emerged towards the end of the thirteenth century and lasted well into the fourteenth. The mullion of a window arcs from the vertical into the window arch, with all neighbouring mullion(s) parallel (or coincident) to it. It is a simple and elegant design, and one that is surprisingly easy to draw.

When plain (i.e. uncusped or unfoliated) this style of window is correctly classified as Gothic Early English architecture, but the addition of cusping or foliation classifies it as a Decorated window.