U+1F743 ALCHEMICAL SYMBOL FOR BORAX-2

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Borax is a salt (ionic compound), a hydrated borate of sodium, with chemical formula Na₂H₂₀B₄O₁₇ often written Na₂B₄O₇·10H₂O. It is a colorless crystalline solid, that dissolves in water to make a basic solution. It is commonly available in powder or granular form, and has many industrial and household uses, including as a pesticide, as a metal soldering flux, as a component of glass, enamel, and pottery glazes, for tanning of skins and hides, for artificial aging of wood, as a preservative against wood fungus, and as a pharmaceutic alkalizer. In chemical laboratories, it is used as a buffering agent.

The compound is often called sodium tetraborate decahydrate, but that name is not consistent with its structure. The anion is not tetraborate [B₄O₇]²⁻ but tetrahydroxy tetraborate [B₄O₅(OH)₄]²⁻, so the more correct formula should be Na₂B₄O₅(OH)₄·8H₂O. Informally, the product is often called sodium borate decahydrate or just sodium borate.

The terms tincal "tinkle" and tincar "tinker" refer to native borax, historically mined from dry lake beds in various parts of Asia.