Decide what type of tattoo design you envision for the necklace. Popular designs are traditional tattoo styles, such as anchors, swallows, hearts and skulls. Japanese tattoo style designs such as cherry blossoms, waves and kanjis are also possibilities. Determine if the necklace is for you or for a friend so that you can better choose the necklace design style.
Rub the fine grit sandpaper in a circular motion on one side of a shrink plastic sheet. Remove dust from the sheet after sanding with a dry paintbrush. Some shrink plastic manufacturers sell shrink plastic with a sanded rough side for convenience.
Draw or trace the outline of the tattoo design with a black marker onto the sanded side of the shrink plastic. Allow the marker to dry. Color in the details of the tattoo design with color pencils. Flip the design over and hold it up to a light. If light shows through the tattoo design, thicken the layer of the color pencils until the design is solid.
Cut out the tattoo design with embroidery scissors. Small scissors work best for navigating shrink plastic corners. Punch a hole at the top of the necklace for hanging. If the necklace consists of more than one design, punch two holes on each side of the designs to connect them with the jump rings.
Bake the shrink plastic according to the manufacturer's instructions. Allow the plastic to cool. Spray the sanded and colored side of the necklace with a clear, spray sealer.
Open a jump ring with jewelry pliers. Thread the jump ring through the hole in the top of the design. Thread the chain through the jump ring. Close the jump ring with the jewelry pliers.