Abstract: Disclosed is a tool for decorating an environmentally friendly surface with an irregular pattern. One way of using the tool is to mount the central pivot onto the mounting for a ceiling light fixture. Applying wet plaster or paint to the area around the central pivot and removing some of the wet plaster or paint in a pattern by manually rotating a marking instrument about the pivot while a cam and arm restrict the movement of the marking instrument to a path that reproduces the contour of one of a selection of cams. The resulting pattern achieves the effect of a medallion that is previously achieved by manually molding plaster or adhering a plastic appliqué to the ceiling.