The adulteration of tea has taken place since the early 1800s. Adulterated tea contains chemicals or additives which, for various reasons, do not belong in the tea - as distinct from flavourings. Adulterants are generally added to tea to reduce manufacturing costs, sell it at a higher price, or deceive the consumer in some other way.
The adulteration of tea on a significant scale started in the early 19th century.
Many substances have been used to adulterate tea. Ordinary substances for adulterating tea include, but are not limited to:
- Prussian blue — a nonsoluble, blue pigment commonly used to color blueprints, crayons, paintings, and paint; it is non-toxic to humans
- Indigo — a blue dye derived from the Indigofera tinctoria plant; it is non-toxic to humans
- Graphite (Plumbago) — a naturally occurring mineral that is a form of carbon; commonly used as the "lead" in pencils
- Gypsum — a soft, naturally occurring mineral; used to alter color of tea
- Soapstone — a naturally occurring mineral composed of talc
In some cases tea that had already been used, and dried, was added to fresh tea.
Laws have been passed to prevent the adulteration of tea. The Adulteration of Tea Act in 1776 was passed by the British Parliament. A similar law against the adulteration of coffee had been passed in 1718. A comparable law was later passed in the United States in 1883.
- Scientific American article 
- Chest of Books 
- UK Tea & Infusions Association 
- An article by Judith L Fisher 
- FSSI.gov.in - DART: Detect Adulteration with rapid test