How to Make Homemade Lye Using Two Ingredients

Make Lye from Ashes and Water

Soap mix being poured
Lye is a key ingredient in homemade soap.

amlanmathur / Getty Images

Lye is a chemical used for making soap, performing chemistry demonstrations, making biodiesel, curing food, unclogging drains, disinfecting floors and toilets, and synthesizing drugs. Because it can be used to make illegal drugs, lye may be hard to find in a store. However, you can make the chemical yourself, using a method popular in colonial days.

The lye you will make with this procedure is potassium hydroxide. Lye can be either potassium hydroxide or sodium hydroxide. The two chemicals are similar, but not identical, so if you are making lye to use for a project, make certain it's potash-based lye you need.

Materials for Making Lye

You only need two ingredients for making homemade lye:

  • Ashes
  • Water

The best ash comes from hardwood trees or from kelp. Softwoods, such as pine or fir, are better if you want to use the lye to make a liquid or soft soap. To prepare the ash, simply burn wood completely and collect the remains. You may also collect ash from other sources, such as paper, but expect chemical contaminants that may be undesirable if the lye is to be used for soap.

Safety Information

You can adapt this method using materials available to you, but keep in mind three important points:

  1. Use glass, plastic, or wood to process and collect the lye. Lye reacts with metal.
  2. The process gives off noxious vapors, especially if you heat the lye to make it more concentrated. Make lye outdoors or in a well-ventilated shed. This is not a project you want to undertake inside your home.
  3. Lye is a corrosive strong base. Wear gloves and eye protection, avoid inhaling vapors, and avoid skin contact. If you splash lye water on your hands or clothes, immediately rinse the affected area with water.

Process To Make Lye

All you need to do to make lye is soak the ashes in water. This yields a slurry of residue in a potassium hydroxide solution. You need to drain the lye water and then, if desired, may concentrate the solution by heating it to remove excess water. In summary:

  • Mix the ash and water
  • Allow time for the reaction
  • Filter the mixture
  • Collect the lye

One method that has been used for hundreds of years, if not longer, is to process lye in a wooden barrel with a cork near the bottom. These are available from brewing supply stores. It's also fine to use a cast iron or stainless steel pot.

To use this method:

  1. Place stones at the bottom of the barrel.
  2. Cover the stones with a layer of straw or grass. This serves to filter the solids from the ash.
  3. Add ashes and water to the barrel. You want enough water to fully saturate the ashes, but not so much that the mixture is watery. Aim for a slurry.
  4. Allow the mixture to react for three to seven days.
  5. Test the concentration of the solution by floating an egg in the barrel. If a coin-size area of the egg floats above the surface, the lye is sufficiently concentrated. If it is too dilute, you may need to add more ashes.
  6. Collect lye water by removing the cork at the bottom of the barrel.
  7. If you need to concentrate the lye, you can either let the water evaporate out of the collection bucket or you can heat the solution. Another option is to run the lye liquid through ashes again.

Modern adaptations of the old technique involve using plastic or glass buckets with spigots rather than wooden barrels. Some people drip rainwater from a gutter into the lye bucket. Rainwater tends to be soft or slightly acidic, which helps with the leaching process.

It's not necessary to clean out the reaction barrel or bucket to make more lye. You can keep adding water or ashes to produce a constant supply of the chemical.