My first attempt at carbon composite resistors was rather simple. I mixed powdered graphite (from pencil leads) with clay, formed it into cylinders and stuck wires in the ends. They showed resistance values well into the kilohm range. I got pretty excited but soon realized a problem. They were far too brittle. they would never have the strength to allow their leads to be bent. The cover picture shows one of these early prototypes with it's resistance being measured. Ways to increase their strength are currently in the works.