Consecutive images are 1/15 s apart. The colour represents the particle ‘displacement area’ δA (see Methods): red implies high crystalline order (low δA), black denotes the fluid phase (high δA), and yellow indicates transitional regions. In the fluid phase, δA is, on average, ≈2.1 times larger than in the crystalline regime. Along with the crystallization front propagating upwards, droplets and crystallites are seen that may grow and then dissolve again. The insets show that their lifetimes increase with area size (measured in units of squared interparticle distance, Δ2). The spontaneous growth and disappearance of crystallites in the fluid regime and droplets in the crystal regime, near the propagating front, are one of the new insights from our study.