How to Make Lye – Lye Water and Soap


Lye is used to make soap, plus it's also found in other cleaners and food.
Lye is used to make soap, plus it’s also found in other cleaners and food.

Here is how to make lye from water and ashes, how to get solid lye from lye water, and how to make soap from homemade lye. Lye made from ashes is potassium hydroxide (KOH). The other type of lye is sodium hydroxide (NaOH). Sodium hydroxide lye is used for hard soaps. Potassium hydroxide lye finds use in soft soap, liquid soap, certain cooking recipes (like olives, pretzels, and bagels), furniture polish, carcass removal, drain cleaner, and oven cleaner.

Materials for Making Lye

You only need two ingredients to make lye:

  • Ashes
  • Water

You’ll get the best results using soft water, like rain water, distilled water, or some types of well water. Hard water contains dissolved minerals that decrease the amount of lye you can extract from ashes.

For making soap or other cleaners or as a food ingredient, use ashes from hard wood. Suitable wood comes from deciduous trees (those that lose their leaves in autumn), such as oak, maple, hickory, walnut, birch, ash, poplar, and cherry. Historically, bracken, saltwort (Seidlitzia), Barilla, Salsola, and Anabasis plants were burned for ash to make lye. So, there’s nothing particularly critical about the ash source, except that some plants contain other compounds that affect the final product. Ashes from softwood (evergreens including pine, spruce, fir, redwood) contain a lot of resin. The resin doesn’t affect the lye, but won’t mix well with fats for soapmaking and affects flavor of food. Softwood lye is great for finishing wood and furniture. You can use ashes from burning paper, but only for uses like drain cleaner. This is because paper contains chemical contaminants unsuitable for use in soap or food.

Safety Information

Lye is caustic. Because it causes chemical burns, it’s important to wear gloves and eye protection. Also, it gives off noxious vapors, so it’s best to make lye (and soap) outdoors or in a well-ventilated area indoors. Lye reacts with metals, including aluminum, cast iron, copper, brass, bronze, and steel. Aluminum, in particular, should be avoided. Stainless steel resists attack, but shouldn’t be used for long-term storage. Ideally, use glass, ceramic, or heat-safe plastic pots. Wooden spoons are fine for stirring, but then should not be used for food. When lye is mixed with water, it’s best to use cold water because dissolving lye is exothermic (releases heat).

How to Make Lye – Method #1

All you need to do to make lye is extract the potassium hydroxide from ashes. It’s easy to do over a grill, campfire, or stove:

  1. Fill a glass or stainless steel pot with ashes.
  2. Add soft water to barely cover the ashes.
  3. Boil the slurry about half an hour.
  4. Let the mixture cool and the ashes sink to the bottom of the pot.
  5. Skim the liquid from the top and store it in a plastic, glass, or wooden container. Discard the boiled ashes and rinse the pot with water to prevent damage. The collected liquid is the lye water. Lye water may be used as-is for some purposes, but may need to be boiled down to concentrate it for making soap.

How to Make Lye – Method #2

Build a leaching barrel to collect larger volumes of lye water. A leaching barrel holds a lot of ash, allows time for lye extraction, and filters impurities out of the lye water.

  1. Use a wooden or plastic barrel with a cork near the bottom (available from brewing supply stores) or a plastic bucket with a nail hammered near the bottom. If you hammer a nail into a plastic bucket, it’s best to leave the nail in the hole until you’re ready to collect the liquid and seal it with tape or wax.
  2. Support the barrel over a bucket or jug. When you un-cork the barrel or remove the nail, you want the lye water to flow into this container. Use concrete blocks, rocks, or wood to support the barrel over the bucket.
  3. Place a single layer of pebbles in the barrel.
  4. Cover the stones with a layer of clean sand. The sand acts as the final filter for the lye water, while the rocks make it easier for the liquid to flow through the sand.
  5. Cover the sand with a layer of dried grass or straw. Tamp it down.
  6. Pour ashes over the straw until the bucket is nearly full.
  7. Press a depression into the ashes and slowly trickle water into the barrel or bucket.
  8. It takes between 6 and 8 hours for the water to make its way through the ashes, straw, sand, and pebbles through the hole in the barrel to the collection bucket. The first lye water is the strongest (can cut grease). As you run more water through the ashes, you’ll get weaker lye. You can pass the weaker solution through the ashes again or boil it down to concentrate the solution.
See how to make lye water from water and ashes.

How to Tell When Lye Water Is Concentrated

Concentrate lye water by evaporating off water, boiling off water, or pouring lye water over fresh ashes.

In ancient and colonial days, people used simple methods to tell when lye water was concentrated. One method is dropping a fresh egg into the liquid. If it sinks, leaving a coin-sized (nickel or quarter) circle of egg floating above the liquid level, it’s sufficiently concentrated to mix with rendered fat to make soap.

It’s better to test the lye using pH paper or a pH meter. The ideal pH is between 12 and 13. The best way to test lye water concentration is with a hydrometer. Most recipes list the ideal specific gravity for the project.

Solid Potassium Hydroxide From Lye Water

Boil lye water in a glass pot to obtain solid potassium hydroxide. Keep in mind, both potassium hydroxide and sodium hydroxide are hygroscopic, so they readily retain some amount of water. Since lye from ashes is impure, boiling off the water generally results in a concentrated semi-solid. Be sure to use safety gear when handling this product and store it in a heat-safe plastic, ceramic, or glass container.

How to Make Soap From Lye Water

Making soap from lye water is as easy as mixing it with fat or oil. When camping, you can make a crude soap simply by stirring campfire ashes and a bit of water into a greasy pan!

  1. The key is to use rendered fat. Obtain this by heating fat, lard, and vegetable oil. The hot liquid is the rendered fat (discard the solid material).
  2. Stir lye water into rendered fat and boil the mixture until it’s thick.
  3. If desired, add color, herbs, or essential oils and pour the mixture into soap molds. Lye from ashes makes a soft soap or even a liquid soap, if you leave in some water. You can get a harder soap by adding salt to the mixture.

Commercial Lye Manufacturing

While making lye from ashes is interesting and fun, industries use different methods to make potassium hydroxide commercially.

One method is mixing potassium carbonate with a strong solution of calcium hydroxide or slaked lime. This is a salt metathesis reaction the yields potassium hydroxide in water (lye water) and solid calcium carbonate. Boiling the lye water gives solid potassium hydroxide, which is also called calcinated or caustic potash.

Ca(OH)2 + K2CO3 → CaCO3 + 2 KOH

Another method of lye synthesis is potassium chloride electrolysis. An electrical current passed through an aqueous potassium chloride solution yields potassium hydroxide in water, chlorine gas at the anode, and hydrogen gas at the cathode.

2 KCl + 2 H2O → 2 KOH + Cl2 + H2

References

  • Cavitch, Susan Miller (1994). The Natural Soap Book. Storey Publishing. ISBN 0-88266-888-9.
  • Lide, D. R., ed. (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton (FL): CRC Press. p. 4-80. ISBN 0-8493-0486-5.
  • McDaniel, Robert (1997). The Elegant Art of Handmade Soap: Making, Scenting, Coloring, and Shaping. Iola, WI: Krause Publications. ISBN 0-87341-832-8.
  • Schumann, K.; Siekmann, K. (2005). “Soaps”. Ullmann’s Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a24_247 ISBN 978-3527306732.
  • Zumdahl, Steven S. (2009). Chemical Principles (6th ed.). Houghton Mifflin Company. ISBN 978-0-618-94690-7.

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