During Solidification (1957-1967), a unified, quantitative framework emerged that integrated nucleation, growth, diffusion, and thermodynamics into a practical theory guiding materials processing. Emphasis was placed on moving solid-liquid interfaces, stability analyses of planar fronts, and the onset of dendritic growth and pattern formation. The period saw cross-disciplinary synthesis across metallurgy, crystallography, and early computational modeling, enabling more predictive control of microstructures in metals and polymers.