Dissolve 1 can commercial lye in 1 gallon cold water. Let mixture stand overnight, then pour the clear liquid into a second gallon of boiling water and bring it to a boil. Pour in a thin stream 4 lbs melted fat heated to the boiling point. Stir constantly until an emulsion is formed. Simmer 4 to 6 hours, then add another gallon of hot water in which is dissolved 1 cup salt. To test for doneness, lift some of the mixture on a cold knife blade. If it is ropy and clear and cools quickly, the mixture is saponified. This makes about 25 lbs white soap.
Dissolve 1 can commercial lye in 10 quarts cold water. Add slowly 3 lbs melted grease. Heat, stirring constantly. Add 1/2 lb borax. Boil and stir until saponified. This takes 4 or 5 hours.
Dissolve 1 can commercial lye in 2 quarts cold water. Heat, add 5 lbs melted grease, stirring constantly. Let stand 24 hours. Add 1 gallon boiling water, set over low heat and boil and stir until saponified.
Source: "Making Soaps and Candles" by Phyllis Hobson