These laboratory experiments are designed to explore aspects of nanoscale chemistry by constructing and spectroscopically analyzing thin films of photonic crystals. Films comprised of colloidal spheres and polydimethylsiloxane exhibit diffraction-based stop bands that shift reversibly upon exposure to some common solvents. Topics covered in these experiments include crystallization and diffraction. This lab is most suitable for undergraduate physical or materials chemistry, though the techniques involved are sufficiently simple for use in introductory chemistry classes. (Contains 4 figures.)