A pearl is nacre wrapped around itself in concentric shells — platelets dense and almost parallel, so instead of glittering it takes one soft narrow shift of hue across its curve. A single pearl shows one answer, because the overtone depends on where you stand relative to that grain. The strand is the demonstration: they are drilled and knotted by hand and no two sit alike, so thirty of them answer thirty ways at once and the overtone walks along the strand as it turns. That is why a string of pearls looks alive where one looks painted.