PH testing- with Turmeric ?

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saqqa

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Hey,
Has anyone heard/tried using TURMERIC for testing PH in their soaps ?
I just saw a youtube, saying it has more reliability compared to the red-cabbage Ph test.

Give your ideas and how you do your PH soap test ?
 

DeeAnna

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We've had quite a few discussions over the years about pH. Some of us have gone to great lengths to explain why pH doesn't tell you anything about whether your soap is skin safe or not. But maybe that's not what you're wanting to know. What do you expect a turmeric or red cabbage or any other pH test to tell you?
 

saqqa

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We've had quite a few discussions over the years about pH. Some of us have gone to great lengths to explain why pH doesn't tell you anything about whether your soap is skin safe or not. But maybe that's not what you're wanting to know. What do you expect a turmeric or red cabbage or any other pH test to tell you?
Really i didnt know about such discussion, would love to know more.
Well, my main reason for pH testing is safety of using the soap.
 

DeeAnna

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That's a reasonable goal, but a simple pH test can't really tell you that.

The pH of properly made soap varies depending on the fatty acids in the soap. You could make 2 different soaps, measure the pH of each one, get an answer of 10.5 for example, and one would be skin safe and the other would be lye heavy.

In addition, a simple pH test is not accurate enough to detect the small amounts of excess lye that would make a soap unsafe for use, even if the soap maker has accurate equipment and does the pH test properly.
 

Mobjack Bay

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That's a reasonable goal, but a simple pH test can't really tell you that.

The pH of properly made soap varies depending on the fatty acids in the soap. You could make 2 different soaps, measure the pH of each one, get an answer of 10.5 for example, and one would be skin safe and the other would be lye heavy.

In addition, a simple pH test is not accurate enough to detect the small amounts of excess lye that would make a soap unsafe for use, even if the soap maker has accurate equipment and does the pH test properly.
@DeeAnna hopefully this isn’t hijacking... I’ve been wondering about the fatty acid effects on pH since it keeps popping up in my reading on the forum. Which fatty acids lead to lower pH soap? Can you point me to a thread that explains why? TIA
 

DeeAnna

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I don't recall that I've discussed this much on SMF. At least nothing is coming easily to mind, so I don't think I can point you toward any threads where I geek out about this topic.

Kevin Dunn's book Scientific Soapmaking touches on this. See Chapter 13, Soaps and Detergents. Looking at the main fatty acids normally seen in soap, pure oleic soap and pure stearic soap have the highest pH values at 11.2 to 11.4. The pH drops off as the molecular length decreases to a pH of 10.1 for pure sodium laurate. The pH also drops off as polyunsaturation increases to a pH of 10.4 for pure sodium linolenate soap.

You can also research the pKa of a soap made from a given pure fatty acid. The pKa value is the specific pH at which 50% of the soap is dissociated into the ionized fatty acid and 50% is intact non-ionized soap. This is not really a soap as we'd want to use, but the pKa is interesting to know if you're wanting to geek out on soap chemistry.

The pKa of a fatty acid doesn't exactly correlate with the pH of the 100% undissociated soap, especially when you're looking at lauric acid and even shorter chain fatty acids. But above lauric acid, the pKa values do roughly correlate with pH values of their pure soaps.

Bear in mind that the information is for pure fatty acids and the soap made from each pure fatty acids. When you make a soap from a mixture of fats, you probably won't be able to fully predict the behavior of this mixed fatty acid soap by relying strictly on info about the pure fatty acids and their soaps.

Not sure I've answered your question, but I hope this gives you something to gnaw on. ;)
 

Mobjack Bay

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I don't recall that I've discussed this much on SMF. At least nothing is coming easily to mind, so I don't think I can point you toward any threads where I geek out about this topic.

Kevin Dunn's book Scientific Soapmaking touches on this. See Chapter 13, Soaps and Detergents. Looking at the main fatty acids normally seen in soap, pure oleic soap and pure stearic soap have the highest pH values at 11.2 to 11.4. The pH drops off as the molecular length decreases to a pH of 10.1 for pure sodium laurate. The pH also drops off as polyunsaturation increases to a pH of 10.4 for pure sodium linolenate soap.

You can also research the pKa of a soap made from a given pure fatty acid. The pKa value is the specific pH at which 50% of the soap is dissociated into the ionized fatty acid and 50% is intact non-ionized soap. This is not really a soap as we'd want to use, but the pKa is interesting to know if you're wanting to geek out on soap chemistry.

The pKa of a fatty acid doesn't exactly correlate with the pH of the 100% undissociated soap, especially when you're looking at lauric acid and even shorter chain fatty acids. But above lauric acid, the pKa values do roughly correlate with pH values of their pure soaps.

Bear in mind that the information is for pure fatty acids and the soap made from each pure fatty acids. When you make a soap from a mixture of fats, you probably won't be able to fully predict the behavior of this mixed fatty acid soap by relying strictly on info about the pure fatty acids and their soaps.

Not sure I've answered your question, but I hope this gives you something to gnaw on. ;)
Yep, that’ll get me started :) I’m having to learn chemistry all over again.
 

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