When structure-property relationships are discussed in inorganic chemistry and materials science, the common perception is that materials with the same composition and atomic arrangement have the same properties. In this laboratory experiment, we show that "processing"--the exact conditions under which materials are made--can in fact significantly alter the properties of materials. Using halide perovskite as a model, we demonstrate that the same set of starting chemicals, when processed differently, can form distinct material platforms--single crystals, thin films, and nanoparticles, the last of these being made of crystallites that are 10,000 times smaller than the first. We then show how this difference in crystal size leads to major changes in the optical properties of the materials, despite the fact that they have the same composition and crystal structure. The experiment provides an example of how the basic concept of crystallization leads to different materials and how processing affects the crystal size and thus influences the structure-property relationship.