Motion of the ordering and aggregation fronts in a dispersion of 198 nm polystyrene particles, with 0.6 mM KCl added.  A 1.1 x 0.8 mm2 area is shown, at 30 times real speed, as viewed under a digital microscope.  The opaque orange region of the film, in the upper section of the video, is liquid dispersion, where unordered particles randomly scatter light.  The green central band contains particles that have crystallized, and are diffracting light in the visible spectrum, but which can be re-dispersed.  The blue area at the bottom of the video contains particles that are irreversibly bound to each other.  The two fronts advance in an intermittent way across the field of view, as the film dries.

Magnified view of a 1.1 x 0.8 mm2 area of drying ludox AM, in a 30 mM KCl solvent, played at 30 times real speed.  The aggregation front is visible as a change in the film color, from dark grey to light grey.  The ordering front cannot be clearly seen under these conditions.  The velocity of the aggregation front is modulated.  When this front accelerates, there is a synchronous advance of the crack tips.   The fringes behind the crack front show where the film de-bonds from the glass substrate.