Diffusion is when molecules travel from an area of high concentration to low concentration. Diffusion can be difficult for a child to visualize, but with Chinese tea eggs diffusion is easily visualized. For a recipe for Chinese Tea Eggs see my cooking blog here. The tea solution is a dark brown color while the egg is white. When diffusion occurs through the cracks of the egg, the egg turns brown. The tea solution is the area of high concentration while the white egg is an area of low concentration. The shell protects parts of the egg from diffusion leaving the egg white if no diffusion occurs (usually occurring if you let the egg simmer for less than an hour) or a little diffusion may occur causing the egg to turn light brown. Using this simple experiment you can allow your child to see diffusion. Plus, Chinese tea eggs taste good. You can experiment with different simmering times to see more and more diffusion occur as time goes on. We let our eggs simmer for 2 hours and the eggs got a little brown under the egg shell while the cracks got very brown.