After being very surprised with the differences between my own pH testing of my bar soaps, and the lab results from the batch analysis, I continue to experiment. I have also purchased a digital pH metre which has become necessary for developing great liquid soap.
I went into the studio today just to do some pH testing and unfortunately the pharmacist/chemist/technical advisor that works with me sometimes, was not with me today. She would have been a great help. We have done some testing together but not since I got my pH metre.
Important to note:
- My results in testing bar soap can’t be that exact as I am testing a solution of distilled water with soap bits mashed up in it. (Liquid soap testing is much more exact.)
- I am not a chemist and am learning from experience and experimenting, not from exact studies.
- I am not really obsessed with the pH in my bar soap. As long as it tests between 9 and 10, and even sometimes slightly over 10, I am fine with it. They are wonderful for the skin. I know that. I have heard of some soapers claiming they achieve as low as a 7. That is not something I am aiming for. I work together with the lab who advise me what is okay and not okay in my results.
Let’s look at the testing for some of my different soaps. First I tried a Castille soap (only olive oil and water). On the right, the soap is 5 months old. On the left the soap is one month old. I only saw a slight pH difference between these two soaps, which struck me as strange and they also seemed to test high all around. For the phenol (Phenolphthalein) test, from the pink, we can see they are over 8, but don't look over 10. Do they possibly look around 9? On the far paper strips, the older soap looks around a 7.5? And the younger soap looks around an 8.5? On the closer paper strips, they both look around a 9? With the digital ph metre, they both tested slightly over 10. I don’t have the lab results back yet.
Orange Poppyseed soap on left. Lemon Sea Salt on right. Both finished 8 week curing period. Phenol makes the pH look quite low, the orange one around 8 or 8.5 and the lemon sea salt soap looks below 8! On the paper strips you can see on the far strips, the lemon salt soap looks around 7 and the orange poppyseed soap looks around 8. On the other paper strips, they both look the exact same around 8 or 9.
Then the pH tests the lemon sea salt soap in at 9.78! and the orange poppyseed soap over 10 – which surprised me because both of these citrus soaps are usually the ones that test lowest on pH from the lab (still always over 9).
So, I calibrated the pH metre again in the 7 and 10 buffer fluids just to make sure everything was right.
Here is my Green Clay-Aloe Vera soap that was made last August. You can see the results here. Phenol looks around 8.5? Both pH strips look around 8 and digital pH reading is 9.69.
Now for making liquid soap, it seems like more of an exact science because I can lower the pH to exactly what I want. As you can see here, from the phenol, it looks like the pH is lower than 8, the paper strips look around 7 and the digital meter reading is 9.29. It first came in over 10, so I lowered it to 9.29 which is right around where I want it.
Conclusions so far from my own testing:
- The various home-pH-testing methods produce wide differences in results
- PH results vary even between different testing-papers
- PH-testing-papers produce falsely low results
- Phenol seems to be the most difficult to deduce an exact pH
- The digital pH-metre tests even higher than the lab results, but the closest to the real pH (assuming the lab results are real)
- In my own testing I only trust the pH metre
- In reality, I only trust the lab results
Ever had your soap tested by a lab for pH and free lye? All of the batches that I sell have to be tested. The results are fascinating and I learn a lot from them.
Questions to you – What pH are you aiming for in your bar soap? Liquid soap? Do you try to lower the pH in your bar soap and with what methods? Anything else you can contribute to help soapers all over would be awesome!!
Happy soaping and pH testing!!