How to make lye solution for soap making

To make lye intended for making soap from scratch, solid sodium hydroxide (NaOH) must be dissolved. Sodium hydroxide beads or flakes are slowly poured into distilled water and carefully stirred until fully dissolved. The lye solution is left to cool. Then it is ready to be mixed with oils. It’s as simple as that! 

Well, it is simple indeed, but since sodium hydroxide is highly caustic, and thus a very dangerous chemical, ultimate care should be taken when handling it. It is highly recommended to familiarize yourself with the properties of sodium hydroxide and its solution and the safest way how to handle it.

Prepare your equipment and workspace in advance, and follow the procedure strictly. Never allow this to become a routine- you need to be careful each and every time as if it were the first time.



-    Water: Use chilled distilled water to prevent generation of excessive heat while lye is dissolving. Soap makers usually use distilled water, but any soft water is fine. Avoid hard tap water due to the minerals contained in it that react with soap molecules making them insoluble, and thus ineffective. 

Experienced soap makers sometimes use liquids other than water (so-called “alternate liquids”), such as milk or fruit and vegetable juices. These liquids contain sugars, proteins and other compounds that require a slightly different technique for making lye solution.

-    Solid (dry) sodium hydroxide: It should be of high purity (at least 97%) and entirely dry and flowable. Avoid clumped sodium hydroxide because it is a sign that it was exposed to air, so that there is an unknown portion of moisture and compounds formed in the reaction between NaOH and carbon dioxide.


Container with sodium hydroxide beads


-    Additives (optional): Some additives like silk, salt, sodium lactate, or certain colorants can be added to water or lye solution in order to enhance their dissolution or incorporation into soap batter. 



-    Safety equipment: When handling sodium hydroxide and lye, wearing gloves, goggles, long sleeves and pants is mandatory. Cover all exposed skin surfaces. Wear such clothing that can be easily and quickly removed in case you spill some lye on it. NEVER handle lye without goggles and gloves.

-    Accurate digital scale

-    Disposable measuring cup (for weighing sodium hydroxide) 

-    Heat-proof, non-reactive container (stainless steel is recommended) equipped with protective handles. Dissolution of sodium hydroxide is an exothermic process - it generates a great amount of heat that your container has to withstand.

-    Stainless steel spoon, with a protective handle for stirring lye during dissolution. Avoid plastic spoons because they melt and deform in contact with hot lye.


Working conditions:

-    Lye should be dissolved outdoors or in some well-ventilated area. When sodium hydroxide dissolves in water, it produces noxious fumes that are caustic and must not be inhaled. If it is done so anyway, lye fumes irritate the lungs. Long-term exposure leads to lung damage.

-    Prevent any distraction when working with lye. Small children and pets must stay away from your working area, preferably out of the room. Turn off the phone; you do not want to be interrupted to answer it anyway.

-    Never leave lye unattended. Lye solution is an odorless and colorless liquid that resembles water. To prevent misidentification, the container holding lye must be clearly labeled and kept somewhere safe, so that no one can reach it and accidentally spill or drink it. Ingestion of lye is often fatal.



-    Wear safety equipment 

-    Weigh cold distilled water according to recipe and pour it into a container where you will dissolve sodium hydroxide. 


Weighing distilled water     Pouring distilled water into heat proof container


-    Weigh your sodium hydroxide beads/flakes accurately into a disposable cup using a digital scale. Do this just before dissolution because sodium hydroxide readily attracts air moisture, which results in formation of crust and clumps. If clumped sodium hydroxide is poured into water, it can cause dangerous splattering. Also, sodium hydroxide readily reacts with carbon dioxide in air to form sodium carbonate, which consumes a certain portion of sodium hydroxide. 


Weighing of sodium hydroxide     Weighed sodium hydroxide and distilled water


-    Take your weighed sodium hydroxide, the container with water and the spoon outdoors or to a well-ventilated area. 

-    Slowly and carefully, pour a small portion of sodium hydroxide into cold water (not vice versa!), and stir gently to prevent any splashing. You should never pour water over solid sodium hydroxide, because it will lead to a very violent, volcano-like reaction. This is because water poured over a pile of sodium hydroxide causes formation of a moist crust on its surface. The water that penetrates inside the pile (i.e. among the beads) causes dissolution of NaOH generating heat. The crust on the surface prevents releasing of heat and steam, which causes the pressure under the crust to increase, and the crust breaks in a violent eruption.

When the first portion of sodium hydroxide poured into water begins to dissolve, the heat starts to generate. 


Dissolving of sodium hydroxide in water


-    Continue pouring sodium hydroxide in small portions and stir to enhance dissolution. As pouring and stirring continues, the lye solution generates more and more heat and it easily can reach 80-90oC (175-195oF) until the end of the process. The hot solution releases steam and toxic fumes, so pay attention not to inhale them. During dissolution, the lye solution becomes cloudy, but this will disappear within a few minutes when it becomes clear again. 


Cloudiness of the lye solution during dissolution in water


If sodium hydroxide is poured suddenly, it can cause water to boil, which is particularly dangerous when it comes to large batches.

-    Stir the lye solution until all sodium hydroxide particles dissolve. When this happens and the lye solution becomes clear, place it in a secure, cold place to cool down.


Lye solution


If your lye cools down more than you need (or if you use master-batched lye), you can re-heat it using warm water bath. Never heat lye on the stove, and never place it in the microwave.