How to Make Lye

Co-authored by Shelley Williams

Last Updated: November 29, 2024 Fact Checked

Lye is an alkaline solution that’s often used for washing, making soaps, and curing certain foods. Lye is sometimes called caustic soda because it has a pH of about 13, which means it’s extremely alkaline and can burn and corrode skin, organic tissue, certain plastics, and other materials. You can make your own potassium hydroxide lye by soaking wood ash in rain water, and this type of lye is ideal for making liquid soaps. Working with lye is dangerous, and requires a number of safety precautions.

Part 1

Part 1 of 3:

Organizing Your Supplies

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1
Collect wood ashes. To make potassium hydroxide lye, you need the white ashes from hardwood fires. When hardwood trees are growing, they draw potassium from the ground. This potassium doesn’t burn in the fire, and is still present in the ashes after the fire. You can then leach the potassium from the ashes with water.^{[1]
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- After every hardwood fire you have, allow the ashes to cool for a few days. Then collect the white ashes and store them in metal containers.
- The best hardwoods for lye water include ash, hickory, beech, sugar maple, and buckeye.
- To make lye using this method, you'll need enough ash to nearly fill a wooden barrel.
- Don’t use ashes from softwood trees, as these don’t contain enough potassium.
2
Collect rainwater. The second thing you need to make liquid potassium hydroxide lye is soft water. Rainwater is ideal because it’s soft and available in large quantities.
- Set up a rain barrel in your backyard or under the eaves of your house to collect rainwater. Make sure there's a filter on the barrel to strain out leaves and organic debris.
- Soft water has lower concentrations of other elements, so it’s ideal for soap making. Hard water will produce soap that doesn’t lather.
- You'll need at least 10 pints (4.7 L) of soft water to make lye water.
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3
Drill holes in your wooden barrel. After you fill your barrel with ashes, you'll run water through the ashes to leach the potassium. The water needs somewhere to drain out of, so you need to make holes. With a drill and a small drill bit, drill about six small holes into the bottom of the barrel.
- Concentrate the holes near the center of the barrel so the water will drain into a bucket.
4
Add a layer of stones and straw. Fill the bottom of the barrel with 1 to 2 inches (2.5 to 5 cm) of clean stones and pebbles. The pebbles should be large enough that they don’t fall through the holes in the bottom. Cover the stones with at least 3 inches (7.6 cm) of dried straw.
- The straw and stones will act as a filter. The lye water will drain down through the straw and stones, leaving the ashes and particles on top.

Part 2

Part 2 of 3:

Making Lye Water

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Transfer the wood ash you’ve collected in your metal buckets to the barrel. Shovel the wood ash over top of the straw. Fill the barrel to within 4 inches (10 cm) of the top of the barrel.
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Prop the barrel up on sturdy blocks. Mount the barrel on sturdy blocks so the holes underneath are accessible. The barrel has to be high enough off the ground to accommodate a bucket underneath.^{[2]
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- You can also mount the barrel inside an open wooden frame.
- Make sure the barrel is sturdy and will not fall over.
3
Position the bucket. Place a lye-safe bucket under the holes in the barrel. This bucket will catch the lye water, so it has to be a lye-safe material. Acceptable bucket materials include:^{[3]
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- Glass
- Stainless steel
- Number 5 plastics
- Heavy-duty plastic
4
Pour rainwater over the ash. Slowly add rainwater to the barrel by the bucketful. You want to add enough water in total to make the ashes wet, but not soaking. If you start to see the water line at the top of the bucket and the ashes are starting to float, stop adding water.
- Pay attention to how many bucketfuls of water you add. This will give you an idea of how many buckets of lye water to expect from the barrel.
- You don’t have to put a lid on the barrel, but make sure that it’s protected from rain in case you get a storm.
5
Put on your personal safety equipment. Lye is very caustic and corrosive. It burns skin, causes blindness, and can damage organic tissue and inorganic materials. When working with lye and lye water, it’s very important to be extremely careful and to wear personal safety equipment, including:
- Goggles
- Hard shoes or boots
- Elbow-length plastic gloves
6
Collect the water that drains out. After a few hours, the first run of lye water will start to trickle out from the holes in the bottom of the barrel. Let the bucket underneath fill up to within 4 inches (10 cm) of the top of the bucket. When the bucket is full, carefully remove it from under the barrel. Be careful not to spill the lye water.
- Replace the bucket with a fresh one to catch the rest of the water.
7
Test the strength. Your lye water has to be a certain strength before you can use it to make soap. The lye water will probably not be ready after a single run, but you can test it. There are four different tests you can use to test the strength of the lye:
- Use pH test strips. You're looking for a pH of 13.
- Use a pH meter to see if the pH is at 13.
- Place a small potato in the lye water. If it sinks, the lye isn't strong enough. If it floats, the lye is ready.
- Dip a chicken feather into the lye. If the feather doesn’t dissolve, the lye isn't strong enough yet.
8
Run the water through again until it’s strong enough. Most lye water solutions will have to be run through the ash barrel at least a second time. If your lye wasn’t strong enough after the first run, carefully pour all the lye water back into the ash barrel. Be extremely careful not to spill or splash the lye water, as it can burn your skin.
- Replace a bucket under the holes in the barrel.
- Let the water drain through the ashes again.
- The lye water that comes out the second time will be stronger.
- When all the lye water has drained through a second time, test the pH again.
- Run the lye water through again if necessary.
Get an unobtainable ingredient. "I build and fly rubber-band-powered model planes as a hobby. The special soap needed to lube the motors has been impossible to find for years. After reading how to make lye water from wood ashes, I realized I could actually DIY the soap myself! Now, my collection of planes can keep on soaring thanks to an ingredient I assumed was history." - John H.

Reduce environmental impact. "As a busy mom trying her best to "go green," I loved learning how I can take two waste items — tallow from the butcher and ash from burn piles — and make my own eco-friendly laundry detergent. I had no clue you could transform scraps sitting around into something useful! Reducing my family's environmental impact took on a whole new meaning when I saw I could make soap with stuff I used to throw out." - Sophia L.

Gain confidence in classic methods. "Who knew you could make lye for soap from ashes in your backyard? I've wanted to try my hand at pioneer-style soap making, but I didn't know how they got the lye way back when. Finding out how to DIY it the traditional way made me feel like I'd unlocked an ancestral secret. And I'm happy to say my ash-lye soap turns out as awesomely effective as any modern store soap!" - Kevin S.

Understand fundamentals of chemistry. "As an at-home tinkerer passionate about science, I used to find chemistry confusing and abstract. But making my own lye water showed me firsthand how you can take basic ingredients from nature, filter and transform them, and end up with fundamental chemical building blocks. Getting this hands-on experience demystified processes that had seemed like magic. I can't wait to experiment more!" - Neil T.

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Part 3

Part 3 of 3:

Using Lye Water

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1
Make liquid soap. Homemade lye water made from potassium hydroxide is ideal for making liquid soaps. You can also make your own castile soap, which uses a lot of fat to make a moisturizing soap.
- Potassium hydroxide lye is not ideal for making hard bar soaps. To make these types of soaps, use sodium hydroxide, which you can buy from home improvement stores, farm supplies, and online.
Cure Olives. There are several foods, such as olives and lutefisk, that are traditionally cured with lye. You can use your homemade lye water to cure olives and other foods at home.^{[4]
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Because lye is so caustic and eats organic materials like skin and hair, it has long been used as a household cleaner and drain cleaner. You can use your lye water to unclog drains in the laundry or utility room, clean bathtub drains, and unclog sink drains.^{[5]
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