The client was an engineer with a deep appreciation for mathematics, and his request was specific: a Penrose tiling for the stairwell window of his 1895 Queen Anne Victorian in Alameda's Gold Coast neighborhood.

Penrose tiling is a system of non-repeating geometric pattern — the shapes cover a surface completely without gaps, but the arrangement never exactly repeats itself. This version uses two interlocking quadrilateral shapes called kites and darts. The window measures approximately 42 by 26 inches and holds several hundred individual pieces, cut entirely in two colors of cathedral glass: pale grey and pale blue.

The discipline of two colors puts all the attention on the geometry. At close range the eye can follow individual pieces; step back a few feet and larger formations appear — pentagons, stars, arrows — shifting and regrouping across the surface. The pattern seems on the verge of resolving into something familiar. It never does.