(Credit: Mark Allan/Barbican)   Long before they looped the décolletés of 1920s flappers, spiraled pearls ran rings around the ocean’s ornamental output in the form of frothy swirls: white whorls whose limpid luminosity brought earthly jewelry into pre-antiquity. Seven tiers of snowy marble in a staircase or a wedding cake can spark a similar entrancement in our ultra-modern times. As {…}