Making Liquid Soap

Okay, so we’re back for part two of my soap-making adventure. In the first part, I made solid soap by the cold process, and if you haven’t seen this, you can either click the link on screen or in the description. If you haven’t seen it, It’s not absolutely necessary but I suggest that you do check it out before this one because I refer back to it quite often. Anyway with that being said, I’m going to move on to making liquid soap using the hot process. To do this I’ll be using the exact same oils as I did for the solid soap, except the base will be different. Instead of using sodium hydroxide, I need to use potassium hydroxide.

I’m also going to be using borax, but depending on the recipe that you follow, it’s not always required. As I mentioned in the first part when I made the solid soap, the recipe I’m doing here is just one of thousands, and you really don’t have to do exactly what you see. The oils that I’m using and the proportions that I’m using can be pretty variable, and I strongly urge you to search online and find the recipe that suits you the best. To get things started, all of the oils were transferred to a slow-cooker When all of the coconut oil is added, I turn it on a low heat and I wait for it to melt. In the meantime I prepare a potassium hydroxide solution.

Potassium hydroxide dissolves much quicker in water and it generates quite a bit of heat, so I didn’t dump everything in at once. It only takes about 30 seconds or a minute for everything to completely dissolve. I wait about 10 minutes for all of the coconut oil to completely liquefy, and then I turn off the heating. Then with some decent stirring, I slowly poured in the base solution. The reaction starts the moment the base is added and it quickly takes on this yellow color.

I mixed it up as well as I could with the spoon, but it’s time to move on to the hand blender. With the cold process, the trace point that I stopped at was important because it determined the additives and the designs that I could use. However with the hot process the reaction is much faster, and it doesn’t really work to stop early on. Even if I ended things now and dumped out the entire batch into another container, the heat of the solution would push the reaction forward and it would thicken up quite quickly. So it really makes no sense to stop early, and the goal with the hot process is to just keep going until it’s a thick trace. The difference between the hot and the cold process is a good example of how heat speeds up reactions.

In the cold process where it’s done at room temperature, it takes about two weeks to go to completion, whereas the hot process only takes a few hours. What’s kind of cool is that there’s a rule of thumb in chemistry where many chemical reactions at room temperature will double the reaction rate for every 10 degrees Celsius increase. The low setting of my slow cooker is about 95 °C which is 70 °C above room temperature. If a doubling occurs every 10 °C, then in theory I should have about seven doublings. With each doubling the reaction time is cut in half, so we can instead think of it as seven halvings in terms of time. In two weeks there are 336 hours and after seven halvings we get to around 2.6 hours.

Considering that the overall reaction here is usually around three to four hours, this is actually pretty accurate. Anyway, once we get to a very thick trace like you see here, the lid is put onto the slow cooker and the heat is turned to low. From this point on it’s pretty simple, and I just need to return every 30 or 40 minutes and give it a good mixing. I need to do this over the course of three or four hours, and throughout this period the soap goes through several different stages. It initially gets a little bit more watery, but then it starts to harden up.

The intermediate stages aren’t super important and the only one that you really need to recognize is the last stage which kind of looks like petroleum jelly. The reaction that’s happening here is the exact same as when I made the solid soap. I’m using a strong base to hydrolyze the ester bonds and split the fatty acids from the glycerol backbone.

The major difference here, besides the heating, is the base that I’m using. Because it’s potassium hydroxide, I’m making potassium fatty acid salts instead of sodium ones. This is one of the major key factors for making liquid soaps. The potassium salted fatty acids tend to be softer and more water-soluble, so they’re easier to be made into a liquid form.

Compared to the recipe in the last video, I also have two other major differences: I’m using much more coconut oil, and I’m also using an excess of base. More coconut oil is used here because it has a lot of shorter fatty acids which tend to form a better lather. A lot of liquid soaps incorporate coconut oil specifically for this purpose.

I’m also using an excess of base here to make sure that the reaction goes to completion However, this does mean that there’s a little bit of base left over in the end Some people don’t really care about this, but it can lead to skin irritation Luckily though because I’m making liquid soap, it can be pretty easily neutralized With solid soap there’s no easy way to neutralize it, so we need to use less than is needed to make sure that it’s all consumed. Eventually, after a few hours I get to this very thick and somewhat translucent paste. If I was making solid soap by the hot process, it would look very similar, and at this point I’d be pretty much done. I’d make sure the pH is below 10, turn off the heat, dump in some additives, and then shove everything into a mold. However, because I’m making liquid soap, there are a few extra steps. To test if it’s done, I weighed out a random amount of soap which was about 11 grams Then I added two times its weight in boiling water and try to dissolve everything.

It took a while, and it was honestly a pain but eventually everything dissolved, and I was left with a nice and nearly clear solution which means that it’s done. If it looks like this, or worse, it should be cooked for another thirty minutes, and then checked again. One of the old methods to test if it was done was to literally just taste the soap.

If there’s a lot of base left over it tastes bitter and apparently gives a zapping feeling on the tongue. I’ve personally never tried this, but I recommend not tasting it and just doing the test I showed before. Anyway, my soap is done, so it’s time to scoop it out.

With only a little bit of difficulty, everything was transferred to a large plastic container. I try to clean up the slow cooker as best I could, but there’s inevitably going to be some that remains stuck inside Then to the soap base, I added 1.2 liters of boiling distilled water. Now for the fun part where I get to try to dissolve all of the soap. It was honestly a pretty big pain and at some point, I felt like it was never going to happen. Some people find that just leaving it overnight and letting it soak in the water can soften things up and make it a lot easier. However, I was impatient so I decided to just brute force it.

The amount of water that’s added here really depends on the dilution level that you’re looking for. If we add up all of the ingredients that I used, we get a total mass of around 1300 grams. So with 1200 milliliters of water the concentration of soap is going to be a little bit above 50%.

I think I pushed the limit a little bit too much because not everything dissolved, and I had to add another hundred mL’s of boiling hot water. They seemed to do the trick and I was able to dissolve everything. So the next thing that I need to do, is to determine whether I need to add some sort of neutralizing agent to get rid of any excess potassium hydroxide. I went ahead and tested the pH, and it came out to be around 9.7 which is probably more than fine, but some people like to lower it closer to around 9.2. In the end though, I don’t think it really makes a huge difference and I’d say the only time that you definitely need to do something about it, is if it’s above 10.

Anyway in my case, I decided I would lower it anyway, and to do this I’m going to use borax. So to a beaker I weighed out 25 grams of borax, and then I poured in 70 milliliters of distilled water. The borax didn’t fully dissolve in the water, but it’s not really a problem as long as there’s no large chunks floating around. Borax isn’t the only thing that can be used here, and it’s common to use other things like citric acid.

The major benefit of borax though, is that it also acts as a thickening agent. With some soaps, even when they’re quite concentrated they can still be a little bit liquidy, and borax can help out with this. It’s also useful if you want to dilute the soap even more, but you don’t want it to be too thin. The borax solution was added in small portions with a lot of stirring in between. At this point the process for making the soap itself is done, and I can now put in some additives if I want.

I could have put in fragrances like cinnamaldehyde or benzaldehyde, but I decided to do something a little bit different. I thought it might be cool if my soap fluoresced, so I dissolved a bunch of fluorescein into water. It turned out that the solution I made was way too concentrated because the small amount that I added here was more than enough. With a little bit of stirring it quickly dissolves and now I have some fluorescent green soap.

It’s important to note though, that if the soap is meant to wash hands or skin, it’s not a good idea to add fluorescein. It doesn’t do anything terrible, but it can be a little bit irritating. I’m using this soap just to wash my glassware though, so it’s not really a big deal. When I’m done mixing in the fluorescein, I put a lid on top of the container and now I wait about a week.

Because I had so much extra fluorescein solution, I decided to play with it a little instead of just dumping it. When it’s poured into water, it can have a pretty cool effect. I’ve actually made fluorescein in the past, and for those of you who are curious I’ve provided a link in the description. Fluorescein fluoresces strongly under UV light, so it’s always cool to check it out under a blacklight. Anyway, this is totally irrelevant to the video and I’m going to get back to the main thing.

Over the course of a week it clears up a bit and any solid material that’s present sinks to the bottom The soap here has a slight orange color because I added a little bit too much fluorescein. In my case though, there weren’t really any solids that came out, so I didn’t have to filter anything. All I did was just pour everything into a proper storage container that I got from Walmart. I also got a soap dispenser, so I went ahead and filled it up.

Now I head over to the sink. I put a little bit into my hands and I try to lather it up. Because I didn’t use too much coconut oil, the lather is honestly not that great, but in general the soap worked pretty well.

As I said before though, the fluorescein in it isn’t great to put on your hands so they were a little bit irritated after this. Anyway at this point, I think I’m done making soap. This is all of the soap from both videos, and I’m honestly pretty proud of what I made. A s I mentioned in my first video, I’m going to be giving away some of the bars of soap, and if you want to enter the contest you can check out the link in the description.

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So if you’re interested, just send me an email or contact me on Twitter, and if I like what I hear I’ll include it.