An important concern when developing new inks containing novel, bulk, solid-state additives is to ensure consistency during the printing process. In particular, the additives should not build up on the rollers, blankets or plates during printing. In this work we describe a method for detecting such events and quantitatively monitoring, in real time, the consistency of developmental inks during commercial printing processes. The technique employs a two-component mixture of emissive nanoparticles whose ratio becomes variable in a non-homogeneous environment. Even tiny variations in the ratio can be readily and dynamically detected in real time using a fibre-optic equipped fluorescence microspectrometer. (C) Koninklijke Brill NV, Leiden, 2010