Ink is a liquid or paste that contain pigments or dyes and is used to color a surface to produce an image, text, or design. Ink is used for drawing or writing with a pen, brush, reed pen, or quill. Thicker inks, in paste form, are used extensively in letterpress and lithographic printing.
There are three basic groups of ink properties: optical properties, structural properties, and drying characteristics. An ink's color is a function of the pigment used, and an ink's other optical properties are primarily determined by the pigment characteristics.