The term “borax” is used to refer both to a mineral and to a refined compound with numerous applications. The mineral takes the form of colorless to white soft crystals, which can sometimes be tinged with brown, yellow, or green. When struck against another material, borax leaves a crumbly white streak. The substance is also known as sodium tetraborate or disodium tetraborate, and it has been known to humans for thousands of years. The mineral is a chemical compound of the element boron, and the chemical formula for borax is Na2B4O7*10H2O.

The word “borax” comes from a Persian word, burak, which was used to refer to borax and other borate salts in the Middle East, picked up by the Romans, and adopted by the Middle English. Borax and related salts were used in the preservation of both food and mummies, as well as to make pottery glazes in China and as a cleaning material. In Medieval Europe, borax was used as a flux in soldering, to scour metal before it was welded together. Borax is still used for similar purposes today, although it is more heavily refined for purity.

While borax is not violently toxic, it can cause skin reactions. Ingestion is also not advised, as even small amounts are not beneficial to human health. Around the house, borax can be useful for cleaning, laundry brightening, and as an insecticide or pesticide. Borax is also used in the manufacture of fire retardants, antiseptics, and fungicides. In the laboratory, borax may be used as a buffer for chemical reactions, since it is a non-reactive base and it will keep chemical solutions stable.

Naturally occurring borax has a high percentage of water. As the water evaporates, the borax becomes more white and crumbly. If allowed to dehydrate, borax will turn into tincalconite. When refined for use, borax is usually broken down and mixed with water, along with a catalyst which will cause the borax to dissolve. Pure crystals of borax will reform, and be ready for packaging or further refining with other chemicals. Kernite, another chemical compound which contains boron, is also refined into borax.

When mixed with sulfuric acid, borax becomes boric acid. Boric acid is used in numerous industrial applications, including cleaning and preservation. Boric acid is also used as a mild antiseptic, and as an eye solution for people experiencing eye irritation. It also marketed as an alternative insecticide, since it is more gentle than some chemical compounds.