An idealized melt crystallizing under crossed polarizers. Set the undercooling — how far below the melting point you hold the melt — and watch how fast the spherulites grow and how many nuclei appear. Deep undercooling: many small spherulites. Shallow: a few large ones. The growth rate itself peaks in between.
Schematic teaching model. The growth rate follows a bell-shaped curve G(ΔT) = Gmax·exp(−KN/ΔT)·exp(−KD·ΔT), the product of a nucleation-driven term (rising as ΔT grows) and a diffusion/mobility term (falling as the melt stiffens) — the qualitative form of secondary-nucleation theory. Nucleation density rises steeply with undercooling, so deep quenches give many small spherulites and shallow quenches a few large ones. The Maltese cross arises from the radial arrangement of birefringent fibrils between crossed polarizers. Neighbouring spherulites stop where their growth fields meet, approximated here by nearest-nucleus (Voronoi) boundaries. The field is a fixed-time illustrative snapshot: it does not solve mass conservation, latent-heat transport, or true impingement dynamics. Values are illustrative, not data for any specific material.