pH Testing on various soaps

[McSpin]

In my quest to understand the value of knowing pH to determine soap safety, I decided to experiment a bit. I'll outline what I did and what I plan to do further.

I have 40+ different soaps here at this time, but some are rather close, so I decided to test 10 of those that seemed the most different.

I have a pH meter that is supposedly accurate to .01 pH. It is rather new, so it should be fairly accurate. At least it has been giving expected readings in all the situations I've used it. I have buffers to calibrate and used a 6.86 calibration solution to calibrate. It was already within a few hundredths of a point before calibration. I then made soap solutions using distilled water and an amount of soap that should have made very close to a 1% soap solution.

The meter was rinsed with distilled water between each soap solution. This is the setup:

After testing several soaps and getting the same reading, I decided to test the 5 that were most different. (the 5th didn't make it into the photo)

Soap A: 28% CO, 55 OO, 17% PO 8% SF - 2.5 months old - pH 10.52
Soap B: 70% OO, 15% CO, 5% Castor, 10% PO, 2 egg yolk/lb, beer instead of water, lavender EO, 3% SF , 3 weeks old - pH 10.48
Soap C: 50% Lard, 30% CO, 20% OO, 2 egg yolk/lb, 5% SF tumeric added, 2 months old - pH 10.48
Soap D: 65% Lard, 20% CO, 10% OO, 5% Shea Butter, 5% SF, Beer instead water, cocoa added, peppermint EO. 4 weeks old - pH 10.52
Soap E: Not shown (laundry soap) 100% CO, minus 2% SF, 8 weeks old - pH 10.35


The laundry soap was the lowest pH I tested and those at 10.52 were the highest. Super Fat varied from -2% up to 8%. I don't do lots of scents and only use natural colorants. I did test 2 HP soaps and they were both 10.47 pH. All of these 5 were CP. I have washed with all of these soaps at least a few times. None have been harsh. Even the laundry soap is fine for washing my hands (at least on occasion).

My next tests will be while processing. I plan to test when I pour, at 24 hours, 48 hrs, 1 week and 4 weeks. I will do this series twice, once on a normal soap and one that is 10% lye-heavy. I'm really curious about the 10% lye heavy soap. I already confirmed that 2% lye-heavy is no big deal with some time before using. I'll update the thread as I get new data.

My initial thought is that my soaps will not vary much in pH.

 

[summerflyy]

I'm wondering if you would also compare with zap test and see if there's a difference between zap testing and pH testing for safety ? This does sound like a very interesting experiment

 

[McSpin]

summerflyy, I'm actually doing this test, because I prefer not to put soap in my mouth (on purpose) and want to find out for myself if pH can be useful for determining when my soap is safe. I have my own doubts about zap testing. I have to wonder if everyone's mouth, saliva, tastebuds, etc are identical. Or, if "zap" occurs at different levels of safety for different people. I also wonder if the lye levels are very low, does "zap" occur or does it only occur at a particular level of lye. For instance, I see a lot of people washing with soap (to test it) when it's 24 hrs old. They say it doesn't zap, but I'm not convinced that 100% of the lye has reacted within 24 hrs. My own hypothesis is that pH will stabilize when the lye has completely reacted. I want to see how it plays out with my soaps over time.

 

[DeeAnna]

I think it's interesting that your results are smack dab within the typical range of pH that I would expect.

If you want the best results from your pH meter, calibrate with two solutions that bracket the expected range of pH. By calibrating only with a pH 6 standard, you are ensuring the acidic range is close, but you might not get optimum accuracy in the alkaline range.

If you only want to calibrate with one standard, pick the standard that is closest to the midrange of pH that you expect to see -- in other words, I'd calibrate with a pH 10 standard for soap.

 

[Seawolfe]

Aye, for my seawater testing we use pH 7 & 10 buffers, because seawater is usually 7.5-8.5

 

[McSpin]

I think it's interesting that your results are smack dab within the typical range of pH that I would expect.

If you want the best results from your pH meter, calibrate with two solutions that bracket the expected range of pH. By calibrating only with a pH 6 standard, you are ensuring the acidic range is close, but you might not get optimum accuracy in the alkaline range.

If you only want to calibrate with one standard, pick the standard that is closest to the midrange of pH that you expect to see -- in other words, I'd calibrate with a pH 10 standard for soap.

This particular pen only has one-point calibration and I would have used a higher pH buffer, but I didn't have one. I am going to pick one up so that down the road, the tests may be more accurate. What I was most interested in seeing was not the actual pH reading, but the fact that out of my many soaps, the pH did not vary enough to make a real difference. I'm wondering what I'd have to put in a soap to get the pH a couple full points higher or lower.

For those interested in doing their own pH tests, I found a rather quick way of making the soap solution. After I add the grated soap to the distilled water, I used a small milk frother. It only takes about 10 sec. of mixing with one, to get the grated soap completely dissolved in the water.

 

[DeeAnna]

Very high in oleic and/or stearic acid => somewhat higher pH up to the mid 11s.

Higher in the other fatty acids normally used for soaping => somewhat lower pH down to mid-low 10s

 

[McSpin]

Very high in oleic and/or stearic acid => somewhat higher pH up to the mid 11s.

Higher in the other fatty acids normally used for soaping => somewhat lower pH down to mid-low 10s

Ah, I didn't think to test my shaving soaps. They are very high stearic acid soaps. I've have to give them a test the next time I'm doing some testing.

 

[McSpin]

I have completed the pH testing at trace, 24 hrs and 48 hours on two soaps with the same formula. The exception being the superfat level. I made one at 5% SF and a lye-heavy one at -10% SF

The formula was similar to others I have made that ended up around 10.5 pH after several weeks.

50% PO, 30% OO, 20% CO, no colorants, a very light amount of Lemongrass EO added to the 5% SF one to make sure it was easy to identify. I measured ingredients very carefully to be as accurate as I could.

5% SF

Medium Trace - pH 11.95
24 hr - pH 11.11
48 hr - pH 10.72

-10% SF

Medium Trace - pH 11.95
24 hr - pH 10.89
48 hr - pH 10.71

I cut both soaps at 48 hrs. The lye-heavy formula was much more brittle and crumbled quite a bit when cut. The odd part was the measurements at 24 hrs. The lye-heavy soap actually tested with a lower pH than the normal soap formula. I don't know why, but maybe I didn't mix it quite as well. It traced a bit faster and not more than a minute of stick blending occurred. By 48 hours they were both at about the same pH. I washed my hands with the lye-heavy soap at 48 hours. I didn't notice any burning or redness in the 4 hours since. I'm thinking that I should have made a 30% lye-heavy soap to see more noticeable differences. I guess I'll do that next. I will still pH test these at 1 week and 4 weeks.

I did test the pH on a shaving soap that was 55% stearic acid and 45% CO. It was 11.18, so I was able to get a reading out of the 10.5 range on a usable soap.

 

[hmlove1218]

Stick your tongue to it and a I guarantee you'll notice a "zap" sensation..

Washing your hands once with a lye heavy soap will only make your hands feel slightly dry. Multiple times and the skin will become so dry that the first layer of skin may start to peel.

 

[McSpin]

Stick your tongue to it and a I guarantee you'll notice a "zap" sensation..

Washing your hands once with a lye heavy soap will only make your hands feel slightly dry. Multiple times and the skin will become so dry that the first layer of skin may start to peel.

Okay, I went ahead and did it. I put my tongue to both soaps and no zap - nada. So what was your guarantee?

 

[MorpheusPA]

Okay, I went ahead and did it. I put my tongue to both soaps and no zap - nada. So what was your guarantee?

Have you ever stuck your tongue to a 9 volt battery's terminals? Free lye gives you roughly the same reaction.

On Saturday, I zap-tested an HP "disaster rescue" batch that wasn't quite done yet. By which I mean there was a lot of free lye.

It not only zapped, it actually burned my tongue--but that's an extreme case and I should have known better.

 

[LBussy]

Well, it sounds like at 48 hours nearly all of the saponification has completed. The pH difference at 24 hours could just have been a bad reading, you'd probably have to take a reading every hour during that time to be able to see if it was.

 

[hmlove1218]

Okay, I went ahead and did it. I put my tongue to both soaps and no zap - nada. So what was your guarantee?

Well I'm glad to see that your soap is safe then.

How old is this soap now? Did it gel or not? Saponification can take up to 72 hours, but can be complete in as little as 24.

 

[McSpin]

Have you ever stuck your tongue to a 9 volt battery's terminals? Free lye gives you roughly the same reaction.

On Saturday, I zap-tested an HP "disaster rescue" batch that wasn't quite done yet. By which I mean there was a lot of free lye.

It not only zapped, it actually burned my tongue--but that's an extreme case and I should have known better.

Yes, I have and it's very obvious. I've also had a lye crystal on my arm that I hit with water and it zapped instantly and clearly. I touched both of these soap formulas to my tongue several times on several bars, and nothing. I even held it there for a couple seconds. From the pH reading, I figured they would both be fine and they were. Initially, I thought the lye-heavy soap was going to take awhile, but it became safe pretty darn quick. Next, I'm going to do a 30% lye-heavy soap to see what happens.

 

[The Efficacious Gentleman]

Interesting. What water amount did you use? I wonder if 10% lye excess with enough water will neutralize like the super lye excess but lots of water Castile experiment

 

[McSpin]

I used the default 38% water in Soap Calc. Even if this wasn't an experiment, I would have noticed something wrong with the lye-heavy soap, but it wouldn't have been the lye. It would be the fact that it was so brittle at 48 hours. To look at it, there was no color difference and no lye pockets that I could see. It will probably make a very good laundry soap.

 

[zolveria]

Dunno. I normally Taste my soap. If it give me tingle metalic taste. like the way a 9volt taste when you lick it. then it needs time. however I have HP soap. and when i taste it they taste sweet. that to me means a cure soap. I normally have a sample soap. that i use to cut layers. and taste. that will gage me to see if my batch needs full 3 weeks or less. I do create my own recipes. and I do not super insulate my soaps. However in the Summer i Do make the most of my soap. AS THE HEAT is my friend and i throw them in the back of my trunk and let them COOK.

 

[McSpin]

I did the 1-week pH tests and got this result:

5% SF Soap - pH 10.38

-10% SF Soap - pH 10.26

I calibrated the pH pen before testing. I also checked a previously tested soap to see if I got the same reading - I did.

The lye-heavy soap is definitely no longer lye-heavy. I washed with it exclusively the past 3 days and it is on the slightly drying side, but I'm betting that many would be happy with it as their regular soap. I'm not expecting to see any change at the 1-month testing interval. pH has gone down, as the lye has been used up from what I can see. It has dropped substantially since the "no zap" results after 48 hrs. It appears to me that "no zap" does not mean "no lye left".

 

[The Efficacious Gentleman]

I'm enjoying this, but wish there was a way of actually testing for lye -

You say it is lye free as you've been using it, but say that it might have had lye even when it didn't zap. So it might well still have lye, even though it doesn't burn during use.

Have you made a hp batch to control any pH changes during curing and so on?