Lab test is detecting 1.1% free alkali detected in lab test.

[Mrinmay Samaddar]

We have followed soapcalc measurements as close as possible. Kept superfatting at 5%. Cured it for 5 weeks before sending the soaps to the lab. Send soaps with two completely different carrier oil recipe. The result is same for both. All other parameters of the test are within permissible limit. No toxicity found. It passed patch test.

Lab advised me to use citric acid.

Can someone advise me on the next course of action please. I have a suspicion that the lab tests might not be accurate.

Any and all guidance will be highly appreciated.

 

[Ekuzo]

The lab results may be true, but what they told you shows they don't know some crucial things when it comes to the making of the products they test.

Citric acid is sometimes used in soap, but its purpose is far different from what they advised you on. It DOES NOT fix lye heavy soap, if that's the case.

That being said, can you share the full recipe with % and weights, as well as the procedure you followed?

 

[Mrinmay Samaddar]

Thanks for the response. Following the is recipe

Olive Oil	45%
Coconut Oil	20%
Grapeseed Oil	10%
Jojoba Oil	5%
Sweet Almond Oil	10%
Castor Oil	5%
Shea Butter	5%

Total weight of carrier oil was 1000gm
Lye used was 133.47 gm and distilled water 248 gm. (as calculated from soapcalc with Superfatting kept at 5%) Added 30 gm of Sodium Lactate to the Lye solution before pouring it to the Oil mixture.

We used cold process. Temperature of oil and lye solution was between 36 and 45 degree centigrade.

 

[DeeAnna]

Recipe checks out at about 5% superfat assuming 100% pure NaOH. If you're using NaOH with less than 100% purity (which is almost certainly the case), then the superfat would be even higher. My feeling is your recipe is reasonably okay.

Other issues to look at:

Is it possible you're using fat that has a much lower saponification value compared with the sap value used by SoapCalc? Soap recipe c@lculators use averaged numbers for the sap values, so there is some inherent error in this. It's not usually a problem, but it's possible it could be.

Are your scales accurate?

If you haven't already, do a thorough zap test. I'd test the top, middle and bottom surfaces of a cut bar as well as splitting the bar open and testing the freshly cut center portion. That will let you know if your soap passes an informal "free alkalinity" test. If your soap really does have 1.1% free alkalinity, your soap won't pass a zap test.

***

Consider is developing an in-house method to do this test if outside testing is a requirement. You don't want to be sending product out to be tested if it can't pass in-house testing.

Here's a non-ASTM protocol as developed by Kevin Dunn for use by small-scale soap makers and also see Dunn's book Scientific Soapmaking for a written version of this method:

Here is a source for an ASTM approved method for use by "real" analytical chemistry labs: https://www.normsplash.com/Samples/ASTM/111295388/ASTM-D460-91-(R2014)-en.pdf You'd want to verify if the test lab is using this method or using another method.

If they're using another method, see if you can get a copy of the method or find the source for the method. ASTM (American Society for Testing and Materials) has protocols that are used worldwide, not just in the US.

 

[Mrinmay Samaddar]

Recipe checks out at about 5% superfat assuming 100% pure NaOH. If you're using NaOH with less than 100% purity (which is almost certainly the case), then the superfat would be even higher. My feeling is your recipe is reasonably okay.

Other issues to look at:

Is it possible you're using fat that has a much lower saponification value compared with the sap value used by SoapCalc? Soap recipe c@lculators use averaged numbers for the sap values, so there is some inherent error in this. It's not usually a problem, but it's possible it could be.

Are your scales accurate?

If you haven't already, do a thorough zap test. I'd test the top, middle and bottom surfaces of a cut bar as well as splitting the bar open and testing the freshly cut center portion. That will let you know if your soap passes an informal "free alkalinity" test. If your soap really does have 1.1% free alkalinity, your soap won't pass a zap test.

***

Consider is developing an in-house method to do this test if outside testing is a requirement. You don't want to be sending product out to be tested if it can't pass in-house testing.

Here's a non-ASTM protocol as developed by Kevin Dunn for use by small-scale soap makers and also see Dunn's book Scientific Soapmaking for a written version of this method:

Here is a source for an ASTM approved method for use by "real" analytical chemistry labs: https://www.normsplash.com/Samples/ASTM/111295388/ASTM-D460-91-(R2014)-en.pdf You'd want to verify if the test lab is using this method or using another method.

If they're using another method, see if you can get a copy of the method or find the source for the method. ASTM (American Society for Testing and Materials) has protocols that are used worldwide, not just in the US.

Thanks a bunch for such a detailed response. Weighing scale is accurate. I have been using a scale to weigh NaOH that gives accuracy to .01 GM.

I have a hunch that either the oil is adulterated or lab test is faulty. I have sent it out to a second lab for testing.

I am very happy with your suggestions of setting up an in-house test facility, but I was in two minds. Your suggestions reinforce and solidifies that I was thinking along the right direction.

Thanks for sharing the resources, as well.

 

[DeeAnna]

...Weighing scale is accurate. I have been using a scale to weigh NaOH that gives accuracy to .01 GM....

Be aware your second statement does not prove the first is true. A scale can weigh to multiple significant digits and still be inaccurate.

You check the accuracy of any scale by using calibrated test weights, not just by looking at the number of significant digits the scale provides.

That said, I would also be concerned about the method used by the outside testing lab. Problem is you don't have any data at this point to support your claim that the soap has no excess alkalinity. In-house testing, both informal and rigorous, is the key.

 

[Ekuzo]

Thanks a bunch for such a detailed response. Weighing scale is accurate. I have been using a scale to weigh NaOH that gives accuracy to .01 GM.

I have a hunch that either the oil is adulterated or lab test is faulty. I have sent it out to a second lab for testing.

I am very happy with your suggestions of setting up an in-house test facility, but I was in two minds. Your suggestions reinforce and solidifies that I was thinking along the right direction.

Thanks for sharing the resources, as well.

Correct me if I'm wrong, but you haven't tried the zap test after it was suggested, have you? That would be the most simple thing to do before you go to a second lab

 

[Mrinmay Samaddar]

Be aware your second statement does not prove the first is true. A scale can weigh to multiple significant digits and still be inaccurate.

You check the accuracy of any scale by using calibrated test weights, not just by looking at the number of significant digits the scale provides.

That said, I would also be concerned about the method used by the outside testing lab. Problem is you don't have any data at this point to support your claim that the soap has no excess alkalinity. In-house testing, both informal and rigorous, is the key.

Understood. We are working in this area as per the suggestions made in your original post.

Thanks a bunch.

 

[Mrinmay Samaddar]

Correct me if I'm wrong, but you haven't tried the zap test after it was suggested, have you? That would be the most simple thing to do before you go to a second lab

You are correct. I am waiting for the new lab test to arrive on Monday. I am also in the process of setting up an inhouse test lab based on Kevin Dunn's method. I am, kind of, not feeling to touch the soap with my tongue. Beat me, kill me, but I am being honest.

Thanks for checking. Really appreciated.

 

[Mrinmay Samaddar]

Correct me if I'm wrong, but you haven't tried the zap test after it was suggested, have you? That would be the most simple thing to do before you go to a second lab

Took the bait and did a zap test. Both my wife and I. We cut open the soaps and checked the center. It was all neutral to the tongue. No sensation at all.

Reports from the second lab test came in today. It 0.11% of free alkali. The regulated standard here is 0.05%. soaps were cured already for over 8 weeks now. Should I increase the superfatting percentage marginally?

 

[Ekuzo]

Took the bait and did a zap test. Both my wife and I. We cut open the soaps and checked the center. It was all neutral to the tongue. No sensation at all.

Reports from the second lab test came in today. It 0.11% of free alkali. The regulated standard here is 0.05%. soaps were cured already for over 8 weeks now. Should I increase the superfatting percentage marginally?

Hmmm that's interesting. I wonder if 0.11% (if it's accurate) should give you zap or not, I wonder what the others have to say. I think it should, and if you didn't get it, maybe your soap doesn't have excess lye, but I may be wrong. My soap bars never gave zap and I don't know at what percentage of negative SF it starts to do it (maybe I should make some lye heavy soap for the sake of testing). Yes, check the scale with some objects you know the exact weight of - I use coins. We have 8 different valued types of coins here and after I weigh them all I know how well calibrated my scale is.

Another thing that comes to mind is if your caustic soda didn't dissolve all the way and left some small crystals in the soap, which you and the lab testers didn't notice (which you should have if that was the case, it's usually pretty visible inside the soap, like white spots within, that zap and you won't think twice whether or not the zap test was positive). Do you strain the lye solution before you add it to the oils, to make sure all impurities and undissolved particles get left out of the batter?

Don't change the recipe for now, 5% SF is usually plenty and gives you enough safety margin. Check the scale and see how accurate it is, also if it's not that difficult, you said you were going to set up the inhouse test lab (I haven't watched the video and I don't know how easy it is). That will help as well, to give you an angle to observe any discrepancies. Maybe both labs give you false tests, who knows (at least it's funny how they both gave you different results, both for positive lye content, while the soap doesn't zap at all).

Check the scale, check for results yourself and let us know, there should be something that can be done. And always strain the lye solution. The way I see it, there may be nothing wrong with the soap.