Bible Dictionary · F
Fuller’s soap
(Heb. borith mekabbeshim, i.e., “alkali of those treading cloth”). Mention is made (Prov 25:20; Jer 2:22) of nitre and also (Mal 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.)
From Easton’s Bible Dictionary (1897), by Matthew George Easton.