How to Make a Lye Solution for Cold Process Soap

By
David Fisher
David Fisher

David Fisher is a highly regarded professional soaper with over 15 years of experience, sharing his knowledge of the craft, science, and chemistry of saponification. He currently owns Bath Rabbit Soap Company and is the author of "The Complete Photo Guide to Soap Making."

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Updated on 09/18/20
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Project Overview
  • Total Time: 1 hr
  • Skill Level: Beginner
  • Estimated Cost: $5

The first and often the most daunting step when making cold process soap is mixing the lye-water solution. The lye solution triggers a chemical reaction that turns the oils of a soap recipe into solid soap. And in that process, the lye—which is a caustic chemical that can burn skin and eyes, as well as be harmful when inhaled—becomes neutralized. However, while you are working with the lye solution, you must do so carefully and take safety precautions.

This tutorial provides the basic steps to make a lye solution. It is fairly quick and easy, even if you're new to making soap. Refer to your chosen soap recipe for the precise measurements of the solution. After you make the solution, you'll be ready to proceed with the next steps of your soap-making process.

Essential Materials for Soap Making

What You'll Need

Equipment / Tools

  • Safety goggles and rubber gloves
  • Kitchen scale
  • Pitcher with lid
  • Mason jar
  • Stainless steel spoon
  • Thermometer

Materials

  • Lye flakes (amount depends on your soap recipe)
  • Distilled water (amount depends on your soap recipe)
  • Sugar or salt (optional)

Instructions

  1. Weigh the Water

    To begin, put on your safety goggles and rubber gloves, and make sure your work space has good ventilation.

    In soap making, everything is measured by weight, even the liquids. Put the pitcher on the scale, and zero out the weight. Then, weigh the amount of distilled water that your soap recipe calls for. Remove the pitcher from the scale.

    Weighing water on a scale in a pitcher
    The Spruce / David Fisher

  2. Weigh the Lye

    Place the mason jar on the scale, and zero out the weight.

    Open the container of lye flakes, and carefully weigh the amount you need in the mason jar. As soon as you have the correct amount, tightly close the lye container and put it in a safe place, so you don't accidentally spill it. Clean up any spilled lye immediately.

    Measuring out lye on a scale
    The Spruce / David Fisher

  3. Add the Lye to the Water

    If your soap recipe calls for adding sugar or salt to the lye solution, add it to the water before you mix in the lye. Stir the water well to make sure the sugar or salt is completely dissolved.

    Now it's time to add the lye to the water in the pitcher. Gradually stir in the lye with your stainless steel spoon, being careful not to splash. Do not breathe the fumes given off by the mixture.

    Warning

    Always add the lye to the water, not the other way around. Adding the water to the lye can cause a volcano-like reaction with the mixture bubbling over.

    Lye being carefully distributed in water
    The Spruce / David Fisher

  4. Stir the Lye and Water Mixture

    Gently stir the mixture until the lye is completely dissolved. The mixture will start to heat up and might even steam or bubble. This is fine, as lye naturally gives off heat as it dissolves.

    Once you're done stirring, rinse the spoon or put it in a container. Don't set it on a table or other surface where it could spread drops of the lye water.

    Lye being gently stirred in water
    The Spruce / David Fisher

  5. Set the Lye Solution in a Safe Place to Cool

    After stirring, put the lid on the pitcher, and set it in a safe place to cool. Be aware that the mixture might be very hot at first—even around 200 degrees Fahrenheit. So don't place it near anything heat sensitive. For added safety, consider labeling the pitcher, so others know what's in it. And keep it away from children and pets.

    The lye solution is ready to use when it cools down to about 100 degrees Fahrenheit. Then, it's time to proceed with making the soap following your chosen soap recipe. 

    Lye water on a hand towel
    The Spruce / David Fisher