Glycerin is a sweet, colorless liquid in its pure form, and is a byproduct of the soap-making process. It is often incorporated back into many soaps and lotions after the soap is rendered due to its moisturizing properties, but is infrequently used in a pure form in commercial soaps because it dissolves too quickly in water and is too soft for many bar soaps. Homemade glycerin is not difficult to make, but involves working with dangerous chemicals and should only be attempted with the utmost care.
Bring 2 oz. water and the sea salt to a boil in a microwave-safe container to create brine; stir well. Set aside to cool.
Put on the neoprene goggles and safety glasses. Lye is extremely caustic and can cause severe burns, rashes and irritation to skin and eyes.
Add the lye slowly to 9 oz. of water in a glass or stainless steel container. Do not add the water to the lye. Stir the mixture until dissolved. At this point a chemical reaction will occur, causing the water and lye mixture to heat rapidly. Allow the dissolved mix to cool to 110 degrees Fahrenheit.
Add the tallow or oil to a large, uncoated stainless steel pot, and heat over medium low temperature until the mixture reaches 110 degrees Fahrenheit.
Add the lye mixture to the oil, pouring slowly as not to splash the mixture. Stir for 15 minutes or until the mixture "traces." Tracing occurs when the batch is thick enough to show the outline of the spoon's path for a few seconds after it passes through. The mixture should have a slightly custard-like consistency.
Add the brine mixture to the lye and oil mix. Stir briefly, and place the mixture in the refrigerator overnight.
Remove the hardened soap layer from the top of the pot. The clear layer beneath is unrefined glycerin, and from here can be boiled to remove excess water, strained to remove impurities, or used as-is in soaps, lotions, creams or hair products.