The human urge for personal hygiene has had many improbable side-effects, and I can confidently assert that through the ages, sponge-divers have punched consistently above their weight. Bronze-age tools, 10th-century Islamic glassware, a Byzantine ship whose plunge to the bottom was cushioned by the fourth-century Roman wreck it alighted upon, anchors, amphorae, sculpture: if it’s down there, they’ll bring it up.