Caustic soda is an alkaline solution that is used to wash, prepare soap and cure certain foods, and gets its name due to its pH of approximately 13. This makes it extremely alkaline, so it can burn or corrode skin and organic tissues, as well as plastic and even other materials. One way to make potassium hydroxide caustic soda at home is by soaking wood ash in rainwater. This type of caustic soda is very good for making soaps. However, it is important that you take proper precautions when working, as handling caustic soda can be very dangerous.
Part 1 of 3: Gather Your Materials
Step 1. Collect wood ash
The ash you need to make potassium hydroxide caustic soda is white ash that is obtained by burning hard wood. Hardwood trees extract potassium from the ground as they grow, which does not burn in fire, so you will find it in the ashes anyway. You can then extract the potassium from them by soaking them in water.
- Let the ashes cool for several days after burning the wood, then store only the white ashes in metal containers.
- To prepare caustic soda, the best woods are ash, pecan, beech, sugar maple and chestnut, among others.
- For this method, the amount of ash you collect should be enough to fill a wooden barrel.
- Softwood doesn't contain enough potassium, so don't use its ashes to make caustic soda.
Step 2. Collect rainwater
After the ashes, you will also need soft water to prepare the caustic soda. To do this, it is best to use rainwater, since it is a type of soft water that you can find easily and in large quantities.
- You can collect rainwater by placing a barrel in your backyard or under the eaves of your house and using a filter to avoid also collecting the leaves and other organic waste that comes along with the water.
- Soft water is a good choice for making soap because of its low concentration of the other elements. On the other hand, if you prepare soap with hard water, it will not create lather.
- You should collect at least 5 liters (10 pints) of soft water.
Step 3. Drill holes in the wooden barrel where you have stored the ashes
You must pour water over the ashes to extract the potassium. However, this water must be able to drain out of the barrel, so it is necessary to drill holes in it. Drill about six small holes in the bottom of the barrel with a small drill bit.
The holes should be in the center of the barrel so that the water can easily fall into a bucket
Step 4. Lay an additional layer of stones and straw
At the bottom of the barrel, place a 1 to 2-inch (2.5 to 5.1 cm) layer of clean stones and pebbles, large enough that they cannot fit through any holes you made. Next, place about 3 inches (7.5 cm) of dehydrated straw on the stones.
This will act as a filter so that the water can pass between the stones and the straw and then through the holes while the ash and other particles remain in the barrel
Part 2 of 3: Prepare Caustic Soda
Step 1. Fill the barrel with the ashes
Transfer the ashes from the metal containers where you collected them to the wooden barrel with a shovel, making sure they reach up to about 4 inches (10 cm) from the top edge of the barrel.
Step 2. Support the barrel on blocks
In order for the water to pass through the holes in the bottom of the barrel, you should place it high up, preferably on sturdy blocks. Make sure the blocks are tall enough to allow you to place a bucket under the barrel.
- If you have an open wooden frame, you can also place the barrel on it.
- You must be careful that the barrel cannot fall off.
Step 3. Place the bucket under the barrel
This should be made of a material that can safely come into contact with the caustic soda, as that is where the caustic will be stored in the first place. Here are some materials you can consider:
- stainless steel
- plastic number 5
- reinforced plastic
Step 4. Pour the rainwater you have collected over the ashes
Do this slowly, one bucket at a time, as you need to pay attention to how much water you add. The water should soak the ashes completely, but not enough to soak them. Therefore, stop adding water if you can clearly see the line of the water's surface at the top of the barrel or if you see the ashes floating away.
- Count the number of buckets of water you add to the ash barrel to find out how many buckets of caustic soda you will get.
- The barrel does not have to be covered unless there is a storm, in which case you should do it so that rainwater does not fall inside.
Step 5. Wear protective gear
Keep in mind that caustic soda is very corrosive, which means that it can burn your skin, blind you, and damage both organic and inorganic fabrics and materials. Therefore, you must be very careful when handling it and use protective equipment such as the following:
- protective goggles
- hard-soled shoes or boots
- plastic gloves that reach the elbow
Step 6. Collect the water as it drains through the bottom of the barrel
This will happen after several hours. When it starts to drain, wait for the bucket you placed under the barrel to fill up to 4 inches (10 cm) from the top. Then remove it carefully without spilling the caustic soda.
Place an empty bucket under the barrel to continue collecting the caustic soda that drains out
Step 7. Test how strong the caustic soda you have produced is
This is because you will not be able to use it to make soap unless it has a certain strength. So the caustic soda is most likely not ready the first time the keg is drained, but you can still test it using one of the following methods:
- Use test strips for pH. This should be 13.
- Use a pH meter, making sure it gives you a reading of 13.
- Dip a potato in the caustic soda. If the potato sinks, this means that the caustic is not yet powerful enough. On the other hand, if the potato floats, this means that the caustic soda is ready.
- Dip a chicken feather in the caustic soda. If the pen dissolves, the caustic soda is ready. Otherwise, you will need to continue draining it.
Step 8. Keep pouring water through the ashes until you get caustic soda of the proper strength
In most cases, you will need to do this at least twice. In case the caustic soda that you have obtained after the first drain has not had enough power, pour it again over the ashes, although this time you must be extra careful when doing so so as not to splash it and burn you.
- Place an empty bucket back under the keg.
- Wait again for the bucket to fill with the water that drains from the barrel.
- The caustic soda that you will get after draining it a second time will surely be more powerful.
- After draining all the caustic twice, retest the pH.
- If necessary, pour the caustic soda back through the ashes.
Part 3 of 3: Using the caustic soda
Step 1. Make liquid soap
This type of caustic soda based on potassium hydroxide is ideal for preparing liquid soap or Castile soap. The latter is a moisturizing soap that requires a large amount of grease.
However, this type of caustic soda is not recommended for making bar soap. Instead, opt for making caustic soda based on sodium hydroxide, which you can easily find at DIY stores, farm supply stores, or online
Step 2. Cure olives
Caustic soda is used to cure a large number of foods, such as olives and lutefisk. Therefore, this is a use that you can give to the caustic soda that you prepare.
Step 3. Unclog the drains
Caustic soda disintegrates organic materials, such as skin and hair, due to its high level of corrosion. Therefore, it is often used to clean drains and also as a general household cleaner. For example, you can unclog laundry drains, clean bathtub drains, and unclog sink drains.