The binary ink developer (BID) in the HP-Indigo press converts low viscosity ElectroInk® into a paste that is presented to the photoreceptor to form the image. The developed mass density depends on the voltage applied as well as the dielectric thickness of the photoreceptor and the paste. For a given ink thickness, less is deposited if its dielectric constant e is lower. In this work we describe a technique to determine the ink impedance over a wide frequency range. From this it is possible to extract e at concentrations near that of the paste in the development nip. For an Indigo-compatible magenta ink, we find that ε ≈ 2, quite close to that of the carrier fluid. The impedance spectra of the ink layer also show features not present in the dilute state, shedding more light on the ink constituents.