salt of tin

Salt of tin is stannous chloride (SnCl₂), a crystalline compound that dissolves readily in water to form a colourless solution. In textile finishing, it serves as a mordant: a chemical that binds dye molecules to fiber, making colours permanent and more vivid. The term is archaic because modern dyers and chemists now use the chemical name directly; "salt of tin" belonged to an era when compounds were often named for their visible appearance or practical role rather than their composition.

The material comes as white or greyish crystals, usually anhydrous or as the dihydrate (SnCl₂·2H₂O). It is highly hygroscopic and oxidizes readily on exposure to air, which limits its shelf life and requires careful storage in sealed containers. When dissolved, stannous chloride is unstable and tends to hydrolyze, forming insoluble tin oxide unless the solution is kept acidic with hydrochloric acid.

The primary industrial application has been in cotton and wool dyeing, particularly with madder reds and other natural dyes. The tin salt is applied as a dye bath or used to pre-treat the fiber. It produces deeper, more fast colours compared to aluminium salts, but excessive use can damage fiber strength and hand-feel, making the work brittle. Concentrations are controlled carefully, typically in the range of 1 to 5 percent by weight of the fiber.

Stannous chloride also appears in tin plating chemistry and as a reducing agent in various industrial processes. In textiles, it fell out of favour after synthetic dyes and superior mordants became standard during the twentieth century. Its toxicity, tendency to hydrolyze, and the environmental hazard of tin discharge also made it less desirable than modern alternatives.

The name reflects period vocabulary: "salt of tin" simply means a chloride salt made from tin metal. You will encounter the term mainly in older technical literature, dye recipe books, and historical accounts of textile manufacture. Understanding the term helps when reading mill records or vintage chemistry texts, but modern practice has moved entirely to systematic chemical nomenclature and safer, more stable mordants.