The invention relates to a method of forming monochromatic or dichromatic copy images with use of a developer composed of a high-resistivity magnetic carrier and a nonmagnetic insulating toner which are triboelectrically chargeable. An electrostatic latent image having at least three different levels...http://www.google.de/patents/US4562129?utm_source=gb-gplus-sharePatent US4562129 - Method of forming monochromatic or dichromatic copy images
