A char containing less than 5% volatile matter is produced by pryolyzing shredded scrap vehicle tires and other rubber scrap material in an externally heated retort until the rubber is completely decomposed and until the temperature of the gases produced by the pyrolysis process reaches at least 500.degree. C. The char is then subjected to resonance disintegration of an intensity sufficient to produce an unltrafine, particulate carbon product. In a preferred embodiment, essentially 100% of the individual carbon product particles are smaller than about 8 microns, and that product displays a dispersion coefficient in rubber of greater than 87%. The surface properties of the carbon product particles may be further modified by reacting or coating the carbon with chemical compounds or coating agents during or immediately after the resonance disintegration to tailor the properties of the carbon product to its use.