Take precautionary measures by protecting yourself from the harmful chemicals you will be subjected to such as the lye, which is corrosive. Use gloves when dealing with high temperatures for protection against heat.
Measure 4 tsp. of lye and pour it into a pot. Add into the pot 2 cups of vegetable oil along with 1 cup of water. You can buy lye from companies that deal with soap ingredients or make it yourself at home from wood ash and water.
Begin heating the mixture and place a thermometer into the pot as you stir frequently. Continue heating the mixture for 20 minutes, until the reading on the thermometer is 125 degrees Fahrenheit. Reduce the heat until the temperature drops to 100 degrees Fahrenheit.
Soak the mixture at this temperature (125 degrees Fahrenheit) and stir for about 10 to 15 minutes. Remove the pot from the heat source after the mixture thickens and add 4 tsp. of salt while still hot.
Leave the mixture to cool while still and you should be able to observe soap forming at the top and glycerin at the bottom. Soap cannot dissolve in glycerin and that's why they appear as so. Separate the mixture by simply poring off the soap or skimming it off if you are not planning to use it again. You may mold glycerin in a desirable shape by using the soap mold then freezing it.