The crafts tradition that produced Islamic geometric designs is most likely based on methods requiring a considerable amount of practical geometrical knowledge. This methodology was understood and practiced by master builders using the traditional tools of the medieval period, such as the compass with a fixed opening (a “rusty compass”), straightedge, and set square for initially creating new designs; and then memorized repeat units for recreating already familiar and well-established patterns. This paper will discuss the re-creation of a specific decagonal star polygon design, using a method proposed by E.H. Hankin, called a “polygons in contact” grid.