Introduction

Ink is a liquid or paste that contains pigments or dyes and is used to color a surface to produce an image, text, or design. Ink can be a complex medium, composed of solvents, pigments, dyes, resins, lubricants, solubilizers, surfactants, particulate matter, fluorescents, and other materials. Pigment inks are used more frequently than dyes because they are more color-fast, but they are also more expensive, less consistent in color, and have limited color range than dyes. Pigments are solid, opaque particles suspended in ink to provide color. Pigment molecules typically link together in crystalline structures that are 0.1-2 μm in size and comprise 5-30 percent of the ink volume. Qualities such as hue, saturation, and lightness vary depending on the source and type of pigment.