Phenolphthalein, pH strips, and Olive Oil Liquid Soap

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Oct 4, 2015
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I am pulling out my hair trying to get my olive oil liquid soap right. Here's my recipe:

24 oz. olive oil
5 oz. potassium hydroxide
5 oz. water
10 oz. glycerin

All went well, soap diluted just fine and was clear as a bell. I tested the pH in three different ways: pH strips, phenolphthalein, using it on my hands to see if it made me super dried out. Results: pH strips showed a pH of 10.5, phenolphthalein showed no pink color, soap felt harsh on my hands. I let the soap sit for a day, tested it again and got the same results.

I thought phenolphthalein showed pink for pH values between 8.2 and 12. This really confused me so I decided to go with the pH strip results. I then added .5 oz citric acid to 2 oz. water and added to the liquid soap to bring down the pH. The soap tested 9.5 on the pH strip and I thought all was good. And it was until the soap cooled off and sat for a few hours. Then, it turned extremely cloudy. So, I added 3 oz. of a 1.1.1 mixture of glycerin, sugar, alcohol to see if that would clear it up. No luck. My soap is more opaque than clear.

Is my understanding of phenolphthalein and the way it works wrong? If not, either the phenolphthalein or the pH strips are not working right. Which one might it be. And yes. The soap was cool each time when I tested it.

Any advice and is there anything I should try to clear up the soap?



Does it zap? That is the only test worthwhile As you have seen, pH testing is not reliable unless it is done properly (which few people do) and even then it doesn't tell you the important things.

1 - is your soap SAFE to use? pH can't answer that by itself, as you don't know what the pH of a recipe should be. You need to test for unreacted lye, the best test for that is to do the zap test, see if the batter on your tongue feels like putting 9V battery on your tongue.

2 - is my soap any good? pH will never tell you that. You can use too low a lye discount or have a generally bad recipe (although Castile like this is a safe bet) and even though the soap is safe, it is not enjoyable to use.

What sort of lye discount did you use? What purity KOH did you use and did you account for that?
Welcome, Kathy! :)

I agree wholeheartedly with the good Gent. When I test my soap, pH is actually the least of my concerns.

Because I'm making lye-based soap, I know it will always test out on the alkaline side of the pH scale, and since the 'safe pH range' of soap can be anywhere from 8.1 to 12.36 (for example, Johnson's has a baby soap with a pH of 12.36 that tested pretty low on the irritability index scale compared to other soaps with a lesser pH, according to a dermatological study cited in Dr. Kevin Dunn's 'Scientific Soapmaking' book), I don't even bother testing pH. The thing I'm really concerned about is whether or not I have unreacted lye in my soap, which will be evidenced by a show of zap.

If you get no zap and the soap feels drying to you, you can cure it for longer, and if that doesn't work, you'll need to change your formula to be more compatible to your skin-type.

The thing with pH strips is that the indicator chemicals on the strips don't play nice with the surfactant nature of lye-based soap, and you can get readings that are 2 or 3 points off the actual mark. And as for the phenol, to test with it properly one needs to make a 1% solution out of the substance being tested first, which most people that I've seen testing soap on YouTube don't even bother to do. And since phenol goes clear above 12 and below 8, how would you really, truly know what range of pH you're looking at? Unlike the above testing methods, the tongue/zap test will accurately tell you in a split second so that you can have no doubt if the soap is safe or not. :thumbup:

IrishLass :)
I see a fair number of people make liquid soap and then try to reduce the pH of the soap to some level ... and I don't understand the basis for deciding a pH of 10.5 is bad but 9.5 is good. Perhaps you can tell me what book or article you and others are using to make this decision?

As far as your particular soap goes -- The cloudiness is due to the soap breaking down into fatty acids in response to the added acid. So perhaps 9.5 is not a good pH for this soap? Try adding 0.4 oz KOH diluted in 0.5 to 1 oz water to the cloudy soap and see if it clears up. If so, I think you will have your answer -- the original pH is what the proper pH should be for this soap.

As far as why the phenolpthalein test didn't flush pink ... I have no idea. You are correct about the indicator turning pink when the pH is between about 8.2 and 12, but I'd have to be standing next to you to really know why your test didn't go as you expected.
I zap test my soap. I went down this whole pH lane long ago, and gave up on it. My soap is either safe or not safe. Zap answers that. If it is safe, I dilute. If it is not safe, I troubleshoot to identify what happened, but I know I can always add a little oil and heat and eventually get a zapless paste.

I am one of those use it as soon as it is diluted folks. There is just no difference to me between a month old soap and one made this morning. But YMMV.
Well, I appreciate everybody's responses. Somebody asked the question about where I got my information to decide that 10.5 pH soap was no good but 9.5 pH soap was good. Heck if I know! Liquid soapmaking is something I'm trying to figure out and the information on the internet is confusing.

The zap test sounds accurate but it scares me. Can I hurt myself? How do I know when to zap?

I like making liquid soap with the glycerin method but don't really know how to tell when the soap is "done". I've found that if I use the glycerin method to make liquid soap, I like the results better - the soap is more emollient right from the get go than soap made with water. I have even tried dissolving the lye in a bit of water first, then adding glycerin (much easier) but the results from the get go are more drying to my hair. I even read somewhere on the internet to add a bit of soap paste to the lye and oils to speed up the process (kind of sounded like yogurt making), so I tried that. I didn't know how much a "little bit" was so I just threw a small chunk in the pot. Oh my! It must have meant a really small chunk because my olive oil paste turned into a stone in about 10 minutes! Then, I wasn't for sure how to check if it was "done" or not so I cooked it for a while longer just to be sure. However, I'm never sure and that's the part I'm trying to figure out.

I saw a post on about testing via titration with phenol, so I did that. I cooked it until the paste didn't immediately turn the phenol bright pink. Is that right? Or do I cook the paste until the phenol NEVER turns pink? And when, along this journey, is it safe to do the zap test? The zap test scares the heck out of me - I kind of like my tongue and want to keep it!

Also, the phenol I have states on the bottle that it's a 1% solution.

People sometimes seem to be scared of the zap test. Really, it's like licking a battery if it does zap. It's already reacted with the ingredients to tone it down, so it isn't like you're licking pure lye water which would be dangerous. Let me put it this way, I once made a cp soap that pooled a bit of liquid on the top. I put the very edge of my pinky to the liquid and it zapped, very strongly (and it did cure out fine and reabsorb). Worst case scenario you have a little irritation on your tongue for a day, and that's only if you zap extremely active soap (which I've experienced too). I've burnt my tongue far worse on hot food far more often than a zap ever has burnt my tongue, though, honest. Touch a finger tip and lick. Easy peasy and very effective in testing soap:) now I just lick instead of the finger because I'm more experienced and know the soap isn't lye heavy, and I'm testing for full saponification after it sat a while so I can unmold and cut.
Phenol is not an acceptable abbreviation for phenolphthalein. Use either phph, or hln. Phenol is a poison, and not an indicator for pH.

Phph is not a good indicator for safe/not safe as it is an indicator for pH, not for free lye. Zap tests for free lye. You can follow the procedure above helpfully posted by lionprincess00. I just take a dab of soap and stick it to my tongue. But then again, I know whether my soap is "done" or not by seeing if it went through gel while I was cleaning the kitchen, so I am taking less of a risk than a less experienced soaper. Do watch your soap after it hits the paste stage. Once you see gel all through it, you are "done". I don't even cook mine.
Ok. Thanks for letting me know about phenol. I used that abbreviation because I didn't know how to spell phenth whatever, whatever, lol! I always have to search around for the spelling. I think I can remember phph, though.
I was just reading a liquid soap making forum on Facebook today and one of the senior members said a pH of 9 was ideal for liquid soap. I won't challenge her to provide proof -- she'll just blow me off -- but I now understand why this idea is ingraining itself into soaping culture as a "fact" (at least on Facebook). And why new soapers are trashing perfectly fine batches of LS in their efforts to get the pH to be "right."

You are all welcome - while not as "scientific" as a good lab with lab grade equipment and controls, I feel it is good enough for the small business/home crafter to get a good understanding of the overall issues with pH and the various testing mechanisms. I did this due to the enormous number of people who totally misunderstand pH, what the limitations on lowering it are in an alkaline product, how to measure it properly and avoid inaccurate readings. I guess I get frustrated sometimes with the number of people who report their soap pH is 7, 8, etc. and then market their soap that way as being superior to other handmade soaps due to the lower pH.