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Soap Making Forum > The Soap Making & Craft Forum > Lye-Based Soap Forum > Phenolphthalein Testing
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Old 06-25-2014, 04:37 PM   #1
DeannaM
 
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Default Phenolphthalein Testing

Hi! I'm still very new to soapmaking (maybe 10 batches under my belt) and I've been using phenolphthalein to test the ph of my soap. Some soaps read fine however, I have had a couple batches that read too lye heavy on the outside but when tested on the inside, even just under the outer layer, they read fine. Any ideas why this might be? Or suggestions? I've just cut the outer layer off and used the soap and no chemical burns just wondering what could be the problem. Thanks!


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Old 06-25-2014, 07:02 PM   #2
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The problem is that phenolphthalein is used for liquid soap not bar soap, and will not give you an accurate reading. Besides pH is not how you test a soap- use the zap test.


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Old 06-25-2014, 11:55 PM   #3
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Phenolphthalein only works in solution. From what I understand, in order to properly test bar soap with it, you must first make a 1% solution by melting 1 gram of the soap in 99 grams of water, and then add the drops to the solution.

Same thing with pH strips- make a 1% solution as above and stick the strip in the solution for about 30 seconds to 1 minute. But you'll want to make sure you are using the best kind of pH strips- i.e., plastic laboratory-grade strips. The reason why is because surfactants (and soap is a surfactant) tend to interfere with the indicator dyes on pH strips, thereby skewing the results. This is less likely to happen with laboratory-grade strips.

But all things considered, it's really not necessary to know the exact pH of a soap. All lye-based soap will test out on the alkaline side of the pH scale. Anywhere between 8 to 10-11 is perfectly within the safe/normal range. Any higher than 11 and you pretty much have a lye-heavy soap on your hands, but that's quite easy to discern without having to resort to the use of pH strips or phenolphthalein. All you need is the tip of your tongue to check for zap, as coffeetime mentioned above. The results are immediate, you don't need to make a 1% solution of your soap, and best of all, it costs nothing.

HTH!
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Old 06-26-2014, 12:27 AM   #4
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It's really mixed, some soapers say that for safety you must check ph. Others say the zap test is just fine.
Both have their issues - lye pockets could be in the soap or lye crystals and unless you frech-kissed your whole loaf of soap you'd never know.
I think for ph phen is more accurate than strips. I make a solution, and I'm not looking for exact ph, just making sure it's not lye heavy/above 11/turning bright fusia.
To be safe, just use both methods. Ive had certain fragrances (sap moss) really burn my tongue but ph tested ok.
To each his own, in the end it's your soap and test it however you want.
The outside might have been high ph because lye heavy soap will sometimes push lye out and a powder forms on the outside of the soap.

Other signs are seizing of soap batter, dry brittle soap, yellow "marbling" and crumbling when cutting.

Last edited by Bex1982; 06-26-2014 at 12:39 AM.
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Old 06-26-2014, 02:12 AM   #5
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I have done many titrations using phenol-p as an indicator, and I have used pH strips and pH meters in industrial applications. I get pretty frustrated about the ways pH strips and phenol-p are being (mis)used in the soaping world.

Some soaps will test bright pink (fuchsia) with phenol-p when the soaps are perfectly fine with no excess alkalinity. And other soaps supposedly have a pH of only 7 or 8 because the indicator or test strip is being used in a way that gives wildly inaccurate results. When there is so much misunderstanding about procedure and so much variability in the results, these pH tests are not reliable measures of soap safety and mildness. In industrial soap making, pH is ~not~ used to determine soap safety -- a titration to measure alkalinity (free lye) is the standard procedure.

There has been a lot of liquid soap that has been cooked to death and a lot of bar soap that has been thrown out or rebatched, all based on "too high" pH test results. I'm with Irish Lass on this issue.
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Old 06-26-2014, 02:16 AM   #6
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Is it reliable when used correctly? I tested phen in lye water to see the color, and in soap sollutions. I feel like if you use it properly it will at least show you if it's too alkaline. I don't really see why it wouldn't ??
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Old 06-26-2014, 09:45 AM   #7
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I've said it before and I'll say it again - as a pH number does not tell you if a bar is lye-heavy (unsafe) or not (safe) then why do it at all? I can see it with liquid soaps in certain processes, but for bar soap it really makes no sense to me - we have to do a safety test (not pH) first of all - but then after that, what is then the point of testing the pH when we know the soap is safe?
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Old 06-26-2014, 10:25 AM   #8
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I zap test bar soap. I can see if the soap has problems that will make zap testing unwise. I do not "french-kiss" my soap. If I think a soap has problems, it gets put into the crock pot and rebatched. No hesitation.

I use a pH meter for liquid soap because when soap paste comes out of the crock pot, it is HOT, and I am impatient. Not because it might be lye heavy.

Most people who pH or phenol-p test liquid soap paste do so because they are going to add a preservative that needs a specific alkalinity range. Preservatives are normally not added to bar soap.

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Old 06-26-2014, 03:19 PM   #9
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"...I feel like if you use it properly it will at least show you if it's too alkaline...."

Ah... There is the 64 dollar issue! What pH is "too alkaline" for a particular soap?

That is a big part of my point. Many people assume a "too high" pH (apparently anything over 8 for some soapers) means the soap has high alkalinity -- in other words, a "too high" pH means there is excess lye in the soap. That MIGHT be true, but it is not necessarily true until one actually confirms that diagnosis by actually measuring the alkalinity.

The "natural" pH of soap generally ranges from 8 to 11. What I mean by "natural" pH is what you get when the soap has no excess lye and low or no excess fat or fatty acids. So let's say we test that kind of soap with phenol-P indicator or pH test strips or a pH meter the way most soapers do, and we get a bright pink blush or a pH of, say, 10. Should we worry about the pH being "too high" and take prompt corrective action (rebatch or neutralize) without any confirmation that this pH is really truly "too high"? Or should we check for zap-or-no-zap, evaluate the texture and visual appearance of the soap, recheck our recipe for accuracy if need be, and move on with life if our other checks seem fine?

I'm strongly inclined to take the latter route. The experience I gained with lye-heavy soaps in a recent SMF thread has shown me that it's not a huge problem to have a soap that is somewhat lye heavy but is otherwise well made. Just give it time. In the SMF super-lye thread, we made soaps with huge lye excesses of up to 45% and found these soaps were zap free after several weeks of cure. Not months of cure ... just weeks. Kevin Dunn of Scientific Soapmaking fame has found the same to be true -- he made soaps with up to a 5% lye excess and found they tested fine -- no excess alkalinity -- after curing out.

Which brings me to this point -- The industry accepted test for excess alkalinity (too much lye) is not pH; it is an acid titration for alkalinity. This test tells the maker exactly how many milligrams per liter of free lye there is in the soap. It can be done, with some care and practice, by the average person in the kitchen. Scientific Soapmaking describes how to do it. If one is determined to test for excess lye, this test is what should be done, not a pH check like most soapers do. If you always made a particular type of soap with a set blend of fats, you could probably correlate that particular soap's alkalinity with its pH and then you could use the pH test as a rough check of alkalinity. But most soapers make a variety of recipes with a wide range of fats. There's no way to do a correlation between alkalinity and pH in that case.
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Old 06-26-2014, 03:39 PM   #10
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Thankful for everybody's help! I guess I will probably just stick with zap testing. I was just a little concerned and didn't want to make soap that would hurt anybody.


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