Making Soap with Lye
In simplest terms, you combine lye, oils, and a liquid to make soap. The liquid may be water, milk, herbal infusions, or any liquid with a relatively neutral pH. Each liquid requires specific soapmaking techniques.
The purpose of liquid in lye soapmaking is to get the lye and the oils together. In solution with water, lye molecules are more easily able to reach the molecules of oil. When they come in contact, the lye and oil molecules all rearrange themselves and become soap and glycerin. If you were to simply add lye to oil, without the liquid, the transformation process would be different, and you'd end up with a big, caustic mess.
In this book, the amount of lye used in a recipe depends on how much of each oil you use. Each oil has a saponification value. This is the amount of lye it takes to turn one ounce of oil into soap. Soap recipes are calculated to make sure they have the proper balance of oils, water, and lye.
Combining Lye with Water
An important step in soapmaking is combining lye with water. This creates an extremely violent, volatile chemical reaction. It is essential that you add the lye to the water rather than the water to the lye. It releases a great deal of energy in the form of heat immediately upon contact. If you pour cold water on top of lye, you could end up with a volcano-like eruption that would be extremely dangerous. When you add water to lye, the chemical reaction causes the water and lye solution to heat almost immediately to nearly boiling. If water is poured onto the lye, it forms a crust over the top of the lye, which seals in the reaction below. The reaction of the lye and water proceeds normally but in a confined space, causing a buildup of heat energy that eventually bursts open like a bomb, showering the area with dangerously caustic material.
Always add lye to cold liquid. The reaction is so violent and rapid that if you add lye to hot liquid, you'll be dangerously close to or over the boiling point in no time. Never add lye to hot liquid.
But even when you correctly add lye to water, do so with care. When you add the lye to the liquid, the solution will heat up very fast and will steam. Do not breathe the steam. Usually it is enough just to stand back and not breathe the steam, but if you are concerned about sensitivity to lye steam, wear a painter's paper dust mask or filter mask over your mouth and nose. If you are very sensitive to chemicals, lye soapmaking may not be for you. Consider one of the methods of making soap at home in which you don't have to use lye.
When you add water to the caustic, the chemical reaction causes the water and lye solution to heat almost immediately to nearly boiling. This can be alarming, and potentially dangerous, but if you pay attention and use your head, you'll be perfectly safe.
Lye Solution Temperature
The lye-and-water solution will heat up to about 180°F. You need to let the solution cool before combining it with the prepared oils. Soapmaking temperatures can range from room temperature (as long as the room is warm enough to keep the oils liquid) to as high as 120°F.
You can take the steaming lye solution outside to let it cool. Just be sure it is in a safe place where no one can get to it and it won't get knocked over. It is also a good idea to cover the container so no leaves or other debris fall into it.
There are some soapmakers who insist that the temperatures of the lye solution and the oil combination must be exactly the same. There are some soapmakers who never even check the temperature. You should start learning your soapmaking techniques by following the temperature guides given in the recipe you are using. After a lot of experience with variations in temperatures, and how those variations affect the process and the product, you can then make your own decisions about how to manage temperature.