The curved surface of a glass of tea
The curved surface of a glass of tea and the liquid within refract and focus sunlight into a bright, concentrated spot, which diffuses into an amber-tinted conical shape. The glass also acts as a prism, creating a miniature dispersion effect along the light pattern’s edges that results in a boomerang-like rainbow.
—Vahid Abbasian, Washington University in St. Louis, St. Louis, MO, USA