In the increased design space of ubiquitous devices, interaction design is challenged by the illusiveness of interactive materials. Traditional design materials do not provide the talkbacks to appraise innovative and highly interactive designs. Interactive prototypes facilitate the appraisal of designs when the interaction idioms are initially unknown. This paper portrays the design process of an app for music creativity. The early stages relied on paper based design materials. The interactive research prototype was built with dynamic script programming. The development from the interactive research prototype to version 1.0 of the app was conduced as a design project. Artists play loops, and create performances to arrange the loops, figure 1. The content is presented on an infinitely large zoomable surface navigated through zoom and pan gestures. The paper contributes to the interplay between design and engineering for artefacts for creative use.