Remove pencil lead with knife. Pencil leads are typically encased in cedar, which splits easily. With a little practice, a pencil lead can be removed intact.
Heat both ends of the pencil lead with a cigarette lighter to burn off any oils and waxes. Buff the ends with steel wool to clean the area where the wire leads will connect to the pencil lead ends.
Secure a nail to a vise and wrap two inches of one end of 6-inch copper wire tightly around the nail. The nail will form the wire into a tight coil at one end. Repeat the process with a second 6-inch length of copper wire.
Gently screw one end of the pencil lead into the short end of one copper coil form. Repeat the process with the other end of the pencil lead into the short end of the second copper coil form.
Melt solder on the copper wire coils using the soldering iron. The solder should flow under and between the wire coils and around the pencil lead, securing the copper wire leads to the pencil lead ends. The carbon resistor is now ready to use. Measure its resistance using the ohmic setting of a digital multimeter.