PH level of soap

[danielle22033]

You won't get a meaningful comparison between products unless you make a measured concentration by weight in water, the same each time. Soap isn't a buffer; the pH of a solution of it is going be concentration-dependent.

I am not exactly sure what you mean by this?

 

[dagmar88]

http://www.millersoap.com/phtome.html

 

[innerdiva73]

I tested my 100% olive oil soap and that too was a 10 with a 8% superfat

The PH in my Olive Oils soaps are always between 7-9. I guess it has a lot with other factors.

 

[dagmar88]

The PH in my Olive Oils soaps are always between 7-9. I guess it has a lot with other factors.

The way you measure. Soap is alkaline by nature. Soap with a pH of 7 is impossible.

 

[innerdiva73]

To the original poster, this info may help if your trying to understand PH and safe levels.
http://www.soap-made-easy.com/soap-ph.html

Just tested one of my 100% OO soap and got a reading of 8. PH strips are not 100% accurate but they can give someone learning the trade a guideline to ensure their soaps are safe for use.

 

[DeeAnna]

"...I always wondered if certain oils influenced the PH...."

Yes, they do. Or actually the mixture of fatty acids in the fats are what will determine the pH. Kevin Dunn in Scientific Soapmaking touches on this. Some excerpts from his book:

"...But even a good, mild, completely saponified soap is generally more or less alkaline, with a pH between 8 and 10. There is a temptation to attach too much importance to the pH registered by the test paper.... [O]ur only consideration is that the soap is not excessively alkaline. We'll refer to such a soap as tongue neutral..." (pp 77 in Section 4.4 The Tongue Test)

"...[T]he pH of a soap solution may vary over a considerable range. Consequently, pH alone will not tell us whether soap contains excess alkali.... [The total alkalinity test is a method of] precisely measuring the amount of excess alkali in soap...." (pp 245-246)

DeeAnna speaking: I'm going to waive my hands over the background behind the numbers listed below and simply say that this is the typical pH range for a soap made out of a single pure fatty acid. These values are taken from page 229 of Dunn's book. Since our soaps are made from mixed fatty acids, you won't see exactly these values.

Lauric acid - Sodium laurate 7.5 - 10.1
Myristic acid - Sodium myristate 8.2 - 10.4
Palmitic acid - Sodium palmitate 8.8 - 10.7
Stearic acid - Sodium stearate 10.2 - 11.4
Oleic acid - Sodium oleate 9.9 - 11.2
Linoleic acid - Sodium linoleate 9.2 - 10.9
Linolenic acid - Sodium linolenate 8.3 - 10.4

DeeAnna again: The point to take away from these numbers is that the absolute lowest possible pH you could ever see is 7.5 and that would be if you made a soap from pure sodium laurate (found in coconut oil). A realistic pH range using mixed fatty acids would be 8 to 10 as Dunn says above.

But pH is not the as precise as it should be to determine whether a soap might be a touch lye heavy or a safe "tongue neutral". A "normal" pH for, say a castile with lots of sodium oleate might be "too high" for a coconut oil soap with lots of sodium laurate and sodium myristate. That is the reason why pH is only a rough indicator -- the "total alkalinity" test is really the proof of the pudding if you want an absolute answer. The zap test is the low tech version of the TA test.

Just to be clear, these pH numbers are for 1% solutions of pure soap dissolved in water and the pH was measured with a properly calibrated lab-grade pH meter. The results from pH test strips rubbed over a damp soap bar won't give you this kind of accuracy.

 

[new12soap]

PH strips are not 100% accurate but they can give someone learning the trade a guideline to ensure their soaps are safe for use.

That is exactly the problem, no they don't. You can easily get an artificially low reading from test strips, they DO NOT accurately tell you the pH of your soap. Beginners learning the trade need to learn how to tell their soaps are safe, absolutely, and the bottom line is that pH strips are NOT going to tell them that.

Please read the link to miller soap about test strips that dagmar posted above.

If you are determined to measure the pH of soap, you are going to have to dissolve some soap in water and use a high quality and accurately calibrated pH meter, but again that will not tell you what you need to know. It is possible for a soap w a pH of 9 to be more harsh than one with a pH of 10, so again, pH really does not help.

 

[Robert]

I am not exactly sure what you mean by this?

There are certain mixtures that are pH buffers. You dilute them and the pH of the solution hardly changes. (If they behaved perfectly according to model, the pH wouldn't change at all. In reality, especially at the high end of concentrations, there are changes.)

Soap is not one of those mixtures. There is no such thing as the pH of a soap. There is only the pH of a given concentration of a soap, a certain weight of the soap in a certain volume or weight of water. As you dilute the soap, the pH of the solution goes down. If you just make lather, you don't know how much soap is dissolved in how much water. You shouldn't vary the temperature either.

The pH strip has a series of pads on it, each of which has a substance or mixture of substances such that a reaction with it will go in one direction or another depending on whether the pH is above or below a certain point. pH strips are particularly tricky when checking alkaline solutions, because carbon dioxide in the air will neutralize more alkali the longer you have the strip out in the air after dipping it.

pH is not the only measure of alkalinity of a soap. When you do the tongue test, you're not just reacting to pH, but to excess strong alkali if they're present. Since what you're probably interested primarily in is how the soap acts on someone's body, it's appropriate to use a sensitive part of the body like that to tell.

 

[innerdiva73]

That is exactly the problem, no they don't. You can easily get an artificially low reading from test strips, they DO NOT accurately tell you the pH of your soap. Beginners learning the trade need to learn how to tell their soaps are safe, absolutely, and the bottom line is that pH strips are NOT going to tell them that.

Please read the link to miller soap about test strips that dagmar posted above.

If you are determined to measure the pH of soap, you are going to have to dissolve some soap in water and use a high quality and accurately calibrated pH meter, but again that will not tell you what you need to know. It is possible for a soap w a pH of 9 to be more harsh than one with a pH of 10, so again, pH really does not help.

Guidelines are what people follow and if someone is trying to get an understanding then Guidelines are what they need. Here is the same article on Miller soap,

"Conclusions:

Not all pH strips are created equal when it comes to testing soap. Some are inaccurate by as much as 2-3 units because the surfactant nature of soap can interfere with the indicator dyes used to make the strips. Others can give accurate readings that approximate those of a pH meter. Based on the pH strips I've tested, laboratory grade plastic test strips are more accurate than paper test strips for testing soap.



Recommendations for using test strips:

Some test strips need longer contact with the solution/slurry for an accurate reading. For best results, keep your test strip in the solution/slurry until the color no longer changes, perhaps 30 seconds or one minute.

Store your strips away from direct light which over time, can fade the dye indicators and interfere with accuracy.


Some people like myself are not comfortable using their tongue to zap test soap.

 

[dagmar88]

Some people like myself are not comfortable using their tongue to zap test soap.

As explained above; even when the pH is accurately measured, that doesn't tell you if there's any excess lye.

 

[shunt2011]

So does making a little lather and touching it to the tip of your tongue. As previously stated the ph strips are not accurate for testing our soap.

 

[sistrum]

The tongue test has been used over a hundred years, even in factories. It's a soap making tradition and the way it's done.

 

[dagmar88]

The tongue test has been used over a hundred years, even in factories. It's a soap making tradition and the way it's done.

I don't get the big deal. If you do everything right, it's not likely you'll get zapped anyway.
I brush my teeth with my soap when I've forgotten to buy toothpaste again.
After a good long cure, it's kind of sweet and not too yucky 8)

 

[JaimeM]

I brush my teeth with my soap when I've forgotten to buy toothpaste again.
After a good long cure, it's kind of sweet and not too yucky 8)

You are a rockstar and my new hero!!

 

[dagmar88]

 

[verotxu]

Hello!

The pH of soap is alkaline because it is made from a strong alkali and a weak acid. In order to get soap with lower pH you should use weaker alkali.

Cheers

 

[dagmar88]

Hello!

The pH of soap is alkaline because it is made from a strong alkali and a weak acid. In order to get soap with lower pH you should use weaker alkali.

Cheers

Could you explain this statement?

 

[DeeAnna]

"...to get soap with lower pH you should use weaker alkali...."

Sooooo ... you're suggesting the use of KOH or NH4OH, perhaps? I'm as curious as Dagmar is -- please explain!

 

[verotxu]

The fatty acids are weak acids and NaOH is a strong alkali. Lets say that the NaOH "wins" over the fatty acids, and there are more OH in the final solution than protons, that is why the pH of the product is so alkaline. KOH is also strong, trietanolamina is weaker though but I have not tried myself

 

[dagmar88]

The fatty acids are weak acids and NaOH is a strong alkali. Lets say that the NaOH "wins" over the fatty acids, and there are more OH in the final solution than protons, that is why the pH of the product is so alkaline. KOH is also strong, trietanolamina is weaker though but I have not tried myself

You need hydroxide to make soap. :wink: No lye, no soap.
Saponification explained in a simple way:

http://www.soap-making-resource.com/how-is-soap-made.html