Question on Preparing a Soap Solution for pH Testing

[Gaspar Navarrete]

Hello everyone,

I got access to a laboratory digital pH meter (costs above $300) that is calibrated regularly with standard buffer solutions. It measures ph to two decimal places. I will be using it to test my soap. I understand it is the most reliable way to test to see if the soap is skin safe.

I also would like to test with phenolphtalein the way a chemist would do it - as a secondary test. I understand this is the way to get the most reliable results from phenolphtalein.

I know that some suggest the zap test. I was using this test for a while. But other soapmakers have written pretty compelling arguments against it on this forum. After reading some of them, my belief in the zap test started to get shaken. I'm now kind of queasy about it.

For the pH meter test or the phenolphtalein test, soapmakers on this forum have said that you need to dilute some soap in a solution first.

Here are my questions:

1. To prepart the solution for testing, how many ounces of soap, and how many ounces of water should I use?

2. Can I use boiling water to dissolve the soap. The higher the temperature of the water, the easier it dissolves.

3. Some soapmakers have said that the solution should also include alcohol (like the 70% isopropyl rubbing alcohol that you get from the drug store). Why ? and how many ounces ?

​

Thanks

 

[AnnaMarie]

This is a DeeAnna question. See if you can lure her out....
Cheers!
Anna Marie

 

[The Efficacious Gentleman]

I still think that a pH test will just tell you the pH. But a pH of x or y does not mean that it is always skin safe or that it is not skin safe. Unless you REALLY want to know the pH for some other purpose (such as for a label) I would just zap test it - it tells you if it is skin safe.

 

[Gaspar Navarrete]

Effaceous Gentleman,

Is there a way to find out the safe pH ranges for the various types of soap ? This way I can use pH to measure skin safety. Also, if the above meter says that the pH is 9-10, that's in the safe range for most soaps.

Regarding the zap test ...

A soapmaker said that the zap test is inaccurate because it depends on the difference between the pH of one's tongue and the pH of the soap. What one ate a few hours ago can change the pH of the tounge.

Another soapmaker said that if the soap has unreacted lye in it, then one might damage the tongue, depending on how often one does the zap test.

 

[Obsidian]

I wouldn't worry about damaging your tongue unless you are zap testing fresh batter. I zap test at 3 days and only rarely get a zap, usually from my salt bars.

PH of your tongue affecting the results sounds like hooey to me. You don't zap test to determine a PH number but to see if there is excess lye.

I've never read anything on this forum against using the zap test, in fact most of the senior members and long time soap makers recommend it as the only sure fire way to make sure your soap is safe.

 

[new12soap]

Effaceous Gentleman,

Is there a way to find out the safe pH ranges for the various types of soap ? This way I can use pH to measure skin safety.

Regarding the zap test ...

A soapmaker said that the zap test is inaccurate because it depends on the difference between the pH of one's tongue and the pH of the soap. What one ate a few hours ago can change the pH of the tounge.

Another soapmaker said that if the soap has unreacted lye in it, then one might damage the tongue, depending on how often one does the zap test.

If you are determined to test your soap's pH that's fine, but the point is that even if you can accurately determine the pH of the soap, you still have not determined the soap's safety. A pH of 10.5 might be perfectly safe, or it may be lye heavy. How will you know the difference? Do not rely too heavily on pH, just knowing the number does not tell you how to correctly interpret that data.

I believe I read the post you are referring to, and that person theorized that different pH levels in your mouth might affect the zap test. Although like with everything else, different soap makers have different opinions and different methods, I have never once heard of any soapmaker not get zapped by the tongue test on a lye-heavy soap, no matter what they ate or drank an hour earlier. Not saying you have to do the zap test, that is up to you, just saying there is a reason that nearly every soapmaker on every forum will tell you that is a reliable indicator.

As for being worried about ingesting lye, first of all you should rinse and spit after the zap test, not swallow. Second, lye is used in many many many foods and in miniscule amounts is not harmful. Olives, mandarin oranges, pretzels, etc are all made with lye.

I am seeing a lot of new soapers get really hung up on the pH of their soap, and IMO it is really not necessary. Learn how to read and formulate good recipes. Learn the process. Learn about the different qualities of different oils and profiles. Zap test or don't zap test, pH test or don't pH test.

I would like to point out the thread here about making an INCREDIBLY lye-heavy soap (on purpose) that in time is curing into a very usable and safe bar. http://www.soapmakingforum.com/showthread.php?t=42922

HTH

Sorry, if you still feel strongly about pH testing your soap, the thread I linked above contains this info provided by DeeAnna

I'm basing my procedure on info I've gleaned from Scientific Soapmaking by Kevin Dunn.

Make a water and soap solution by dissolving about 1 gram of soap in about 100 grams of distilled water. Super accuracy is not required. Definitely do not use tap water -- distilled or reverse osmosis water only.
Calibrate the meter with pH 7.0 and 10.0 standards.
Be sure everything is more-or-less at room temperature to avoid adding error due to temperature to your pH check.
Test per the instruction manual.

To the best of my understanding, the soap should have a "natural" pH roughly between 10.7 and 11.2 if made with olive. If it has excess alkali, the pH will be higher than that.

I do not know if those numbers only correlate to that recipe, tho.

Oh, and as for phenolphthalein, all that tells you is whether something is alkaline, and soap will always be alkaline.

 

[Gaspar Navarrete]

new12soap,

In the link you provided, a soapmaker said that the excess lye reacts slowly with the carbon dioxide in the air to make a carbonate. I did not know this.

Another argument for giving the soap ample time to cure after the HP cook.

Thanks, this was an eye opener.

A pH of 10.5 might be perfectly safe, or it may be lye heavy

I have a hard time understanding why this is so.

 

[FlybyStardancer]

Because different formulas of soap will have different 'natural' pHs. For instance, formula A might be at a pH of 10.5 with all of the lye reacted, but formula b would have a pH of 10.2. If you're making formula a and get 10.5, then you're good to go, but if you're making formula b, then it's lye heavy at 10.5. Part of the problem is that we don't know what the pH should be for each soap, because it's dependent on the fatty acid profile of the oil, and we have no way of testing that at home.

 

[Gaspar Navarrete]

FlybyStardancer,

... but there are several webpages out there that have the fatty acid profile for all the common oils soapmaking used for soapmaking (like this one). We don't need to test for that at home, because apparently it's already been done.

With the information from such webpages, one could be able to get an estimate for the fatty acid profile of the soap recipe that one is currently making.

Does each fatty acid have a natural pH ?

 

[new12soap]

SAP values are averages. Agricultural products will have some variance. Last year's olive oil from Spain will be different than this year's from California. The range for olive oil is 184-196, for coconut oil it's 250-264. What is the exact sap value of the oils in your pantry? Good question.

This is why I keep singing the same refrain; make batches of 1.5 to 2 lbs of oils, and use at least a 5% superfat. You NEED that margin to cover those variations as well as any small inaccuracies in measuring.

And this is also why it is extremely difficult for the home soaper to calculate exactly what the correct pH should be and measure it accurately and consistently.

 

[FlybyStardancer]

From this page, olive will usually have between 63-83% oleic acid. Sunflower can have 40-74% linoleic acid. And on and on... Do you have any way of knowing what that year's growing climate, location, nutrients, and water levels all gave the oils that you're planning on using? I sure don't.

And if you're using olive oil, it might be even more complicated thanks to all of the adulterated oils on the market.

 

[Susie]

I am a nurse, so I sort of get the desire to get a quantifiable pH that you can guarantee is safe. And if you were dealing with laboratory made ingredients, then it might even be possible. But you aren't. So, the best you are going to get is a range of what is safe. And that is a kind of wide range if you are a perfectionist(like me).

I am very, very glad that I was introduced to the zap test before finding out about phenolpthalien(or however you spell that) or a pH tester. That way, I routinely know that my soap is safe or not safe without obsessing over numbers or shades of pink(that I have a hard time determining).

 

[Gaspar Navarrete]

You all raise good points, especially about the oils having variances in them.

I'll continue to use the zap test, since the majority endorse it.

I just want to be able to look someone in the eye and say my soap is safe. The manufacturers of the store-bought soap care about delivering a safe product, they care about doing the job right, and they test their soaps accurately and thoroughly. They have to, because they have to meet all kinds of regulations, and answer to alot of people. Like the manufacturers, I also have to be not sloppy. If my soap isn't done right, it can be worse than the store-bought soap. And this is what is in the back of my mind. This is my motivation behind all my questions about phenolphtalein and pH meters. I suppose I was overreacting with the pH meter and the phenophtalein.

I devised a test to be used alongside the zap test. While the soap is curing, make a concentrated solution of that soap and water. Dip some aluminum (or tin) foil in the solution, and let it sit there for a week or so. If there is excess lye in your soap, you should see a discoloration in the foil. If all the lye has been used up, the foil should remain shiny. Do you all think this test can work ?

 

[FlybyStardancer]

They also have the resources to do intensive testing, and I doubt their soaps are superfatted! Don't stress so much. It's harder to screw up and get a lye-heavy soap than what you're fearing. And there are also recipes that are deliberately lye-heavy, like the castile thread floating around.

 

[DeeAnna]

"...If all the lye has been used up, the foil should remain shiny. Do you all think this test can work ? ..."

No, Gaspar, that will not work, because just the dissolved oxygen in plain water is sufficient to discolor aluminum foil. And soap, even skin-safe soap, is likely to discolor the foil even more so than water. And ... take a moment to think about this carefully -- just how does a piece of discolored aluminum foil specifically relate to skin safety?

"...Like the manufacturers, I also have to be not sloppy...."

The implication of your comments is that you honestly don't believe handcrafted soapmakers are capable of making good, safe soap using the simple procedures and tests we are sharing with you. Do you really, truly mean that?

 

[AnnaMarie]

My foil will discolor when I use it to cook food. By your logic my food shouldn't be safe, but it is. I'm not thinking discolored foil is a good indicator.

 

[Gaspar Navarrete]

Okay, nevermind about the aluminum foil test. You all made some good points. I did not think about that.

DeeAnna, I do not mean that. Someone (not online) who believes in store-bought soap over handmade, made a slighting comment about my soap and it kind of stuck. I guess I should have phrased that better. Now that you point it out, I can see that it was that person who was speaking instead of me. That happens with me sometimes.

I have learned quite a bit from everyone in this forum, and I meant disrespect to no-one.

 

[AnnaMarie]

Make your soap and be proud. Ignore those who make light of what you do. You will occasionally have to deal with such people, and nothing will defend what you do better then being proud of your creations and knowing they are good quality. Those who are serious about this do set high standards and make good soap. It sounds like you are headed that direction- keep going
Cheers!
Anna Marie
Ps- IMO, a lot of these comments are deflecting from the real issue: people comprehending that good soap does cost money. A lot of people simply don't understand the cost of doing business.

 

[DeeAnna]

Gaspar, thank you for your thoughtful reply. I can relate to your experience. Comments like this say far more about the speaker than about the listener, but it can certainly be hard to keep that perspective in mind! I agree with AnnaMarie's advice -- it's wise and sound.

 

[The Efficacious Gentleman]

If you want to look someone in the eye and tell them that your soap is safe, look them in the eye as you lather up with it (maybe just your hands, rather than in the tub!) and then look them in the eye as you give that bar of soap a great big lick. Explain to them that the pH of soaps varies a great deal and that the best proof is that YOU use it.