This is a classic demonstration of diffusion-controlled reaction kinetics combined with coordination chemistry. On one side is iron(II) sulfate (FeSO4), providing Fe²⁺ ions. On the other side is potassium ferricyanide (K4[Fe(CN)6]), which contains the hexacyanoferrate(II) complex. As both solutions slowly diffuse through the medium, their ions begin to meet at the interface. When Fe²⁺ encounters the ferrocyanide complex, a coordination reaction occurs, forming an insoluble iron cyanide complex. This precipitate appears as an intense colored pattern that grows over time. What makes this visually striking is that the reaction front is not instantaneous. It is governed by diffusion rates, concentration gradients, and local supersaturation. This creates branching, fractal-like growth structures rather than a uniform color change. Key concepts at play: • Diffusion: movement of ions from high to low concentration • Coordination chemistry: metal ions binding to ligands like CN⁻ • Precip...