A new technique is described for following the effects of successive increments of oxidative attack upon the same particles of carbon black. Oxidation was carried out under controlled conditions outside of the microscope, followed by electron micrography of selected grid areas. Electron micrographs show that normal thermal and furnace blacks generally oxidize from the inside out, forming capsules of unchanged external dimensions. Differences in rate of oxidation of individual particles are observed with thermal blacks; these rates are, however, independent of particle size. In agreement with earlier evidence, graphitized thermal blacks oxidize from the outside in. Strong support is given for a new “concentric crystallite” model of carbon black microstructure. On the basis of this model, slippage of rubber molecules on the surface of carbon black can be readily understood.