What Is Lye?
All soap is made with a caustic called lye. Home soapmakers use two kinds of lye: sodium hydroxide, which is used to make solid soap, and potassium hydroxide, which is used to make liquid soap. In this section you will learn about each.
Sodium hydroxide (chemical formula NaOH) is what most people mean when they say “lye.” Sodium hydroxide is easily available in 18-ounce plastic cans at grocery, hardware, and restaurant supply stores. It is generally stocked alongside the drain cleaners. Do not buy anything other than pure sodium hydroxide. There are other drain cleaners available, but they include substances that are not at all suitable for soapmaking. You may also purchase sodium hydroxide from soapmaking suppliers. It is considered a hazardous material, and there are restrictions to the amount you can order through the mail. Check with the supplier for the regulations in your area. If you plan to make a great deal of soap, it is a good idea to find a local supplier where you can buy lye in bulk.
Because it is an ingredient in the manufacture of the dangerous illegal drug methamphetamine, also known as “meth” or “crank,” sodium hydroxide is controlled in some states. People who manufacture large amounts of soap, and therefore need to keep large amounts of lye on hand, must register it with local agencies.
The level of safety precautions you take depends on many things. The safety of children and pets is a primary concern. If you live with an adult with special needs, you must also take that situation into consideration. Educate them not to touch the lye safe and to stay away from cooling lye solutions while you are making soap.
Store your sodium hydroxide in a safe, dry place. The space under the kitchen sink is not a good idea, especially if you have kids. Many home soapers have a “lye safe” just for lye storage. Lye safes can range from a box in the garage clearly marked “Lye! Do Not Touch!” to a metal cabinet with locking doors.
You can make a practical and easy-to-create lye safe from a plastic storage box with a tightly fitting lid. Label it clearly and store it where you think is safest in your home. Storing your lye safe on a high shelf isn't necessarily recommended, since you can easily drop it, especially if you keep over a few pounds at home. Keeping it on the floor of a closet can work, as can the floor of the garage. If you find yourself worrying a great deal over the safe storage of your soapmaking caustics, perhaps you should employ one or more of the techniques that do not use lye. Pay attention to your intuition.
In your lye safe, keep the plastic cans of lye in plastic bags. Label three bags: one for unopened cans, one for partially used cans, and one for empties. Take care how you dispose of empty containers. Neutralize the lye dust by rinsing the containers with a vinegar-and-water solution. If you have a hazardous material drop-off day in your community, take your empty lye cans to the collection point.
Potassium hydroxide (chemical formula KOH) is a type of caustic used to make liquid soap. It is important to note that potassium hydroxide and sodium hydroxide are not interchangeable in soap recipes. Different amounts of each are needed to saponify the same amount of fats. If you make both liquid and solid soaps, be sure to keep your instructions and saponification charts for each clearly marked.
Potassium hydroxide is more difficult to find than sodium hydroxide. You can order it from soap supply houses and buy it at chemical supply stores. As usual with soapmaking, the Internet is your best resource. Store potassium hydroxide as you would sodium hydroxide, in a safe spot and clearly labeled.