Sheets of cut lines stacked over each other, one to each colour of the set. ?Every sheet is a card with the spaces between a few dozen straight strips cut away, and the corners where two strips cross are rounded, as a knife leaves them when it turns rather than stops. There is one sheet to each colour of the set, the lowest the first, each a gap above the one under it, so the light throws every sheet’s shadow on the next. A mask cuts a hole through all of them and leaves a strip round its edge; the lower sheets are cut a little smaller, so a hole is a flight of rims.