The form of the "Shuang Shan Guo" is extremely difficult to master. The straight body cylinder exhibits roundness within its firmness, possessing both bone structure and flesh. The curved spout extends with proper measure, creating a lively rhythm. According to Professor Gao Yingzi's recollection, Gu Jingzhou once spent an entire morning completing the body cylinder, yet pondered over the lid and handle for nearly three months. He had his own simple yet vivid understanding of grasping the balance of form and the essence of spirit: > A Yixing teapot is balanced, so it must have coherent energy (*guanqi*) in its balance. If a teapot lacks coherent energy—if the handle is too thick and the spout too thin, or the spout too thick and the handle too thin—then it lacks this coherent energy. ... When [a teapot] possesses harmonious form, harmonious spirit, and energy—these three elements—when the energy flows coherently and the form is beautiful, then it has rhythm (*yun*). It's just like music: do, re, mi, fa, sol, la, ti—when sung together, there is rhythm.[1] --- [1] Wuxi Radio and Television Station: *Zisha Master Gu Jingzhou* (CD), 2010