The term potash is generally used to describe potassium carbonate (K₂CO₃), a compound used since earliest times for making soap. It is a hygroscopic material typically supplied as small, granular crystals.

Potash, like soda ash, was produced by running water slowly through the ashes of burned plants and then boiling down the resulting solution in large pots--hence the term, from pots and ash. Potash was one of the first products to be exported by the American colonists, being shipped from Jamestown to England as early as 1608. Since they had thousands of acres of forests to remove in order to create farmland, the colonists had an enormous supply of ash, from which they created the potash that was so in demand by English industry for soap and glass making. The colonists also used potash to make soap for their own use. Because potassium carbonate and sodium carbonate are very similar, potash was used interchangeably with soda ash in soap and glass manufacture. When the Leblanc process of producing cheap synthetic soda was developed in the 1790s, industrial demand for potash waned.

Today, commercial supplies of potassium carbonate are prepared from the mineral sylvite, a compound of potassium and chlorine, much of which is found in New Mexico. In addition to its use in soapmaking, it is used in the production of glass and pottery. It has also been used in the lithography process and for liquid shampoos.