Despite common misconceptions, people living in medieval times had bathtubs and soap. Soap-making devices dating from the 700s have been excavated in Arabia, and the European Mappae Clavicula—written in the early 800s—includes soap-making directions. With care and some experimentation, modern crafters can recreate the soaps used in medieval times.
Collect ashes and spread them over wickerwork or sieve. Clean pot thoroughly. Place pot under wickerwork or sieve. Gently pour hot water over ashes so it drips into pot. Heat collected lye water. Pour over same ashes two to three times to increase its strength and color.
When well-strained, boil lye for a long time, until thick. Add olive oil and stir very well. If desired, add lime. Let lye boil until cooked down and reduced to thickness. Allow to cool. Work the soap with spade for two to four days until well coagulated and dewatered. Lay aside for use.
Tallow soap. Follow same steps as above, but substitute beef tallow for oil. Add wheat flour if desired. Let lye cook to thickness. Add salt. Cook lye until it dries out.
Measure 2 parts alkali and 1 part un-slaked lime. Break lime into chestnut-size pieces. Cut hole in bottom of one pottery pot; seal hole tightly with rag. Break bricks into pieces and pack into pot. Place fabric on bricks; cover with alkali and lime. Add water equal to four or five times pot's submersion volume. Place pot in high location with empty second pot under outlet. Let ingredients sit for one day and one night. Open outlet on second day; allow filtered liquid to flow into empty pot. Re-seal hole. Pour filtered water back into first pot; allow to sit for another day and night.
Divide clear liquid in half. Set one half aside. Into remaining half, pour an equal amount of sesame oil and beat strongly with beater for 1 hour until hard and thick. Allow mixture to ferment for two to three days. Put soap into cauldron and place over a strong fire. When soap thickens, add small amounts of reserved water. Continue heating soap and adding water until grainy and ripe. Beat as needed to prevent burning.
Take soap off fire; pour into large pot. Beat, adding water little by little. Replace mixture in cauldron and return to fire. When beginning to dry out, add water little by little, stirring to prevent burning. Continue until all reserved water is used. If desired, add choice perfumes to soap while cooking. When finished, soap should be well-cooked with consistency of shoemaker's glue.
Spread cloth and place mold over it. Pour soap into mold. Leave soap for at least one night and one day or until solid. Cut soap with knife into desired size pieces.