An ink is a liquid containing various pigments and dyes used for coloring a surface to produce an image, text or design. Ink is used for drawing and writing with a pen, brush or quiill. Ink is a complex medium composed of solvents, pigments, dyes, resins, lubricants, solubilizers, surfactants, particulate matter, flourescsers.
Dye-based inks are generally much stronger than pigment-based inks and can produce much more color of a given dentsity per unit of mass. However, because dyes are dissolved in the liquid phase, they have a tendency to soak into paper.
Cellulose, the material that paper is made of, is naturally charged, and so a compound that complexes with both the dye and the paper's surface will aid retention at the surface. Such compound in common use in ink-jet printing inks is polyvinyl pyrrolidone.
An additional advantage of dye-based ink systems is that the dye molecules interact chemically with other ink ingredients. Because dyes get their color from the interaction of electrons in their molecules, the way in which the electrons can move is determined by the charge and extent of electron delocalization in the other ink ingredients. The color emerges as a function of the light energy that falls on the dye.
References
~"A History of Technology and Invention", by Maurice Audin
~Martin-Gil J, Ramos-Sanchez MC " Chemical composition of a fountain pen ink", Journal of Chemical Education
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