How it works
The picture is made in two passes, and keeping them apart is most of the job. The macro pass paints: a handful of large lumpy shapes are laid down in flat ink on the cream of the paper, each one wandering sideways from the one above it.
The micro pass carves. Lines are drawn over the ink in the colour of the paper, so they read as channels cut out of a solid area rather than as marks laid onto an empty one. Painting ink-coloured lines onto cream would give a picture that has to cover the whole sheet to look like anything, because bare paper then reads as a hole; carving cream out of ink lets the ground simply be ground.
Within the ink, the lines are offsets of each shape’s own outline. Every sample on a grid is labelled with the frontmost shape covering it, then measured for its distance to the nearest sample belonging to something else, and that distance field is contoured at an even interval. A distance field rises at the same rate everywhere, so the gaps come out even without being made even; the lines run parallel to the edge, because that is what a distance contour is; and they stop dead where one shape crosses another, because cells straddling a boundary are refused.