Fuller's soap

Easton’s Bible Dictionary

Fuller's soap : (Heb. borith mekabbeshim, i.e., "alkali of those treading cloth"). Mention is made (Proverbs 25:20; Jeremiah 2:22) of nitre and also (Malachi 3:2) of soap (Heb. borith) used by the fuller in his operations. Nitre is found in Syria, and vegetable alkali was obtained from the ashes of certain plants. (See SOAP.)