Expressive interfaces that communicate human emotional state (e.g., level of arousal) are beneficial to many applications. In this work, we use a research-through-design approach to learn about the challenges and opportunities involved in physicalizing emotional data derived from biosignals in real-time. We present EmoClock, a physicalization that uses a clock as a metaphor to communicate arousal and valence derived from biosignal data and lessons learned from its evaluation.