Celadon does not arrive; it is negotiated. The green depends on iron in the glaze, on the reduction atmosphere of the kiln, on the thickness of the application, and on the patience of the person holding the tongs at the peep hole. Too little iron and the surface is a pale grey, pretty and forgettable. Too much, and the green turns to brown, the color of a forgotten pond. The sweet spot is a fraction of a percent wide. Collectors speak of the drip — the point where a heavy application gathers and runs, darker and denser than the body above it. It is the glaze's signature, the place where chemistry admits it is also choreography. On the shelf after firing, a celadon cup holds the light the way a wet leaf does. Rain on jade, the old catalogues said. Close enough — and no less true for being a little sentimental.