Marseille soaps or Savon De Marsielle is a traditional hard soap from Marseille, France. Its popularity spans 600 years and is recorded in history as far back as 1370.
Traditionally, the soap is made by mixing sea water from the Mediterranean Sea, olive oil, and the alkaline chemicals soda ash (sodium carbonate) and lye (sodium hydroxide) together in a large cauldron (usually making about 8 tons). This mixture is then heated for several days, stirred constantly. The mixture is allowed to sit until ready, then poured into a mould and allowed to set slightly. While still soft it is cut into bars, stamped, and left to completely harden. The whole process can take up to a month.