barium strontium lead magnesium or aluminum such carriers are disclosed in u s pat nos 4 042 518 4 478 925 and 4 546 060 carrier particles can be uncoated or can be coated with a thin layer of a film forming resin to establish the correct triboelectric relationship and charge level with the toner employed examples of suitable resins are the polymers described in u s pat nos 3 547 822 3 632 512 3 795 618 and 3 898 170 and belgian patent no 797 132 other useful resins are fluorocarbons such as polytetrafluoroethylene poly vinylidene fluoride mixtures of these and copolymers of vinylidene fluoride and tetrafluoroethylene see for example u s pat nos 4 545 060 4 478 925 4 076 857 4 726 994 and 3 970 571 polymeric fluorocarbon coatings can aid the developer to meet the electrostatic force requirements mentioned above by shifting the carrier particles to a position in the triboelectric series different from that of the uncoated carrier core material to adjust the degree of triboelectric charging of both the carrier and toner particles the polymeric fluorocarbon coatings can also reduce the frictional characteristics of the carrier particles in order to improve developer flow properties reduce the surface hardness of the carrier particles to reduce carrier particle breakage and abrasion on the photoconductor and other components reduce the tendency of toner particles or other materials to undesirably permanently adhere to carrier particles and alter electrical resistance of the carrier particles in a preferred embodiment the carrier is sponge iron which is sieved oxidized and coated with fluorocarbon on a 0 1.