The physical parameters of colloidal carbon particles in an insulating liquid have been measured by several independent techniques. The particle size and charge, the Debye screening distance, and the interparticle distance are found and are used to interpret the electrographic development process (toning). The nature of the developed image depends upon the magnitude of the initial surface charge density and upon the time in the toning bath. The optical density for full development of an electrostatic charge image is shown to be proportional to the charge density in the image indicating that arriving particles overlap in a random manner. Measurements on the development process as a function of time shows that particles are being drawn out of the colloid in the intermediate range where both diffusion and mobility must be considered in determining the motion of the particles.