Sketch the design to be piped onto a piece of paper, and place the paper underneath a clear acetate sheet.
Table the chocolate to be used for piping to temper it, then let rest for 10 to 15 minutes to cool and thicken. Fill a piping bag with the tempered chocolate, and begin to pipe the chocolate onto the acetate sheet to fill in the design. If the chocolate is the right consistency, it should not be necessary to outline the design first.
Continue piping until the entire design has been filled in. For any areas of the piece that should appear thicker than the rest, pipe over the design a second time to create more volume.
To add small, simple accents to the design with a different type of chocolate, dip the point of a paring knife into the tempered chocolate and dot it onto the surface of the piped design before the piped chocolate sets. This is much faster than preparing another piping bag. If more complex accents are desired, however, fill a separate piping bag with the tempered chocolate and pipe directly onto the surface of the piped design before it sets.
Let the chocolate set until it begins to curl up a bit and release itself from the acetate. As soon as it is set, remove the piece from the acetate and store at room temperature until ready to use.