Ink is a liquid or paste, containing dyes or pigments, used for writing or printing. Writing ink dates from the 3rd millennium BC in China and Egypt. The most common today is blue-black permanent ink, made by dissolving gallic acid, iron (II) sulfate, and tartaric acid in water. Since the blue-black color is produced only when the ink dries, a dye is usually added to color the ink during writing. In ballpoint inks, dyes are dissolved in glycols and other liquids, and wetting agents added. Black waterproof India ink is a suspension of carbon particles stabilized by gelatin, glue, etc. Carbon black is also the pigment used in black printing ink. Printing inks – diverse in their composition and uses – are viscous pastes made by grinding pigments with varnishes or petroleum solvents, and contain various additives for printability and drying speeds.