An experimental study of the development of carbon black dispersion by an internal mixer and its characterization is presented. We describe the measurement of carbon black agglomerate size and related characteristics using four different experimental techniques : optical microscopy, scanning elctrion microscopy, surface roughness, and electrical couductivity. The results from these different experiments are compared uning the same carbon black for a series of six different butadiene-styrene copolymers. The results from the different techniques are cross plotted and are critically discussed. It is found that surface but then sharply deteriorate. At subsequent stages of mixing optical microscopy seemed the most reliable measure.