When that field is turned off, the suspension quickly returns to the equilibrium fluid state - at least, most of the time. Larsen and Grier, however, have seen colloidal crystals remain intact for up to an hour after most of the suspension has returned to a fluid state - even though the colloidal spheres have like charges and have no reason to cling together in the absence of an electric field. How the metastable crystallites remain intact for so long is not yet understood. Their longevity is not caused by the inhomogeneities in the properties of the glass surfaces, because the crystals are observed to drift across the glass surfaces on which they form. The reason for the spheres' behavior, however, has yet to be explained.
Dark trajectories are part of the crystal and light are in the fluid.
Grier has a preprint of Larsen's and his findings available online.