Eastman Kodak Company has recently announced breatkthrough nanoparticulate ink technology which represents an improvement in both dye-based and pigment-based inks. These ultrafine pigmented inks exhibit average particle size approximately one order of magnitude smaller than other commercially available pigmented ink jet inks. In this article, we will discuss the effects of colorant particle size on reliability, image quality, and durability in an ink jet printing system. Comparisons will also be made to conventional dye-based inks.