Easton's Bible Dictionary: M. G. Easton, M.A., D.D.
Fuller's soap
(Heb. borith mekabbeshim, i.e., "alkali of those treading cloth"). Mention is made (Pr. 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)
Original from The Bible Foundation - bf.org. They claim public domain status for their original text.