Mold and stamp clay beads. Knead clay between the palms of your hands until smooth and pliable. For each napkin ring, form a 3/8-inch-thick cube-shape bead measuring 3/4 inch x 1 inch. Press the leaf button into the clay on the top of each bead to imprint pattern. (If a leaf button is not available, draw or trace a small leaf pattern onto tracing paper; cut out. Center pattern on bead, and use a needle tool or toothpick to carve around the pattern. Remove pattern; carve veins in leaf.)
Make holes and bake beads. To make holes in beads, push the skewer through the centers horizontally. Leave beads spaced on the skewer, and place it on a baking dish so the ends of skewer rest on the sides of the dish, allowing the beads to hang without touching the bottom of the dish. Bake beads according to clay manufacturer's instructions; cool.
Finish with varnish and ribbon. Apply varnish to all sides of each bead, using a paintbrush; let dry. Remove beads from skewer. Thread a length of ribbon through each bead. Wrap each napkin holder around a folded napkin, tying the ribbon in back. If desired, insert a fall leaf between the napkin ring and napkin.