in an apparatus for printing images on a moving primary imaging member by jetting ink , containing a fluid and marking particles , in an image - wise fashion onto the primary imaging member , a device for concentrating the ink prior to transferring a marking particle image to a receiver member . the ink concentrating device includes a fractionating unit for separating fluid of the ink from the marking particles . the fractionating unit is located a predetermined spaced distance from the primary image bearing member . an electrostatic field is established between the primary image bearing member and the fractionating unit for concentrating the marking particles in the liquid of the ink .