"Direct visualization of aging in colloidal glasses"
Rachel E. Courtland and Eric R. Weeks, J. Phys: Cond. Mat. 15, S359-S365 (2003).

We use confocal microscopy to directly visualize the dynamics of aging colloidal glasses. We prepare a colloidal suspension at high density, a simple model system that shares many properties of other glasses, and initiate experiments by mechanically stirring the sample. We follow the motion of several thousand colloidal particles after the stirring and observe that their motion significantly slows as the sample ages. The aging is both spatially and temporally heterogeneous. Furthermore, while the characteristic relaxation time scale grows with the age of the sample, nontrivial particle motions continue to occur on all time scales.