This talk presents an overview of the composition Purity (1994), one of three movements in the composition Clang-tint, commissioned by the Japanese Ministry of Culture and the Kunitachi College of Music, Tokyo. The pitch structure of Purity is based on the Bohlen-Pierce (BP) scale. I chose the full chromatic BP scale because of its intriguing sound. With its combination of intervals that were both sweeter and more sour than 12-note equal temperament, I saw strong potential for expressive melodic and harmonic structures. The ear is the most sophisticated sound analyzer we know, and it was by ear that I mastered the BP scale, a process that took many months. In Purity, the BP scale is embedded in a context of broader pitch strategy involving freely flowing glissandi and echo effects.