The name ‘tannin’ comes from the French tanin = tannin and covers a group of natural polyphenols. In English and French, the term taninns not only includes gallotannins (previously used to describe gallic acids), but tannins in general.
Tannins are derived from gallic acids. Tannin (synonyms: galotanic acid, tannic acid) is a yellowish-white or brownish powder with a distinctive smell and pungent taste. It is soluble in water, ethanol and acetone but is insoluble in ether and chloroform. In conjunction with ferric chloride solutions, the aqueous tannin solutions form precipitates of a blue-black type of dye (iron-based inks). Tannin is a very effective tanning agent, a feature exploited for thousands of years in the leather industry. Tannin can be used in the human body, applying on the wound and inflamed skin, which helps protect the affected areas (reducing capillary permeability in the skin).
Tannin is used mainly for dyeing animal skins, but it is also used for medicinal purposes. Due to its astringent characteristics, tannin is used to treat diarrhea (although in high doses it can produce adverse effects), as well as an antiseptic, an antidote (with the exception of morphine, tannin solutions precipitate several heavy metals and alkaloids) and as an elliptical (coagulation agent). In the dye industry, tannin is used as a mordant for cationic dyes, while it is also used in the manufacture of colors and as a purifier of fruit juices, beers and wine (refining agent). Tannin is also used to treat boiler water, in photography, in adhesives and as a coagulant of materials during rubber production.