We present here a sculpture metaphor for rapid shape-prototyping. The sculpted shape is the iso-surface of a scalar field spatially sampled. The user can deposit material wherever he desires in space and then iteratively refine it using a freeform tool. The tool shape can be designed inside the application. The tool can add, remove, paint or smooth material, or it can be used as a stamp to make prints on an existing shape. The user can move the scene and/or the tool with a Spacemouse (6D input device), or a 2D mouse using virtual trackball. We also focussed on the rendering quality, exploiting lighting variations, and environment textures that simulate high quality highlights on the surface. Both greatly enhance the shape estimation, which is in our opinion a crucial step during the design process. We also explored some stereo configurations to improve the user's perception of the spatial relationships between the elements of the scene. Our current implementation based on GLUT allows the application to run both on UNIX-based systems, such as IRIX and Linux, and on Windows systems. We obtain interactive response times, strongly related to the size of the tool. The performances issues and limitations are discussed.