Phenolphthalein Testing

Discussion in 'Lye-Based Soap Forum' started by DeannaM, Jun 25, 2014.

  1. Jun 25, 2014 #1

    DeannaM

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    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 :D just wondering what could be the problem. Thanks!
     
  2. Jun 25, 2014 #2

    coffeetime

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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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  3. Jun 26, 2014 #3

    IrishLass

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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!
    IrishLass :)
     
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  4. Jun 26, 2014 #4

    Bex1982

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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: Jun 26, 2014
  5. Jun 26, 2014 #5

    DeeAnna

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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.
     
  6. Jun 26, 2014 #6

    Bex1982

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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 ??
     
  7. Jun 26, 2014 #7

    The Efficacious Gentleman

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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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  8. Jun 26, 2014 #8

    Susie

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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.
     
    Last edited: Jun 26, 2014
  9. Jun 26, 2014 #9

    DeeAnna

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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.
     
  10. Jun 26, 2014 #10

    DeannaM

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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.
     
  11. Jun 26, 2014 #11

    The Efficacious Gentleman

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    I'm with you on that one - my horror batch from last weekend needs some rest before it's ready for use, I know - and hurting people is the last thing that we are looking to do. Which is why I zap test, so I know if the soap is safe.
     
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  12. Jun 26, 2014 #12

    DeeAnna

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    Yes, Deanna, I truly understand your concern. Well designed recipes that are mild to the skin, good ingredients, a reputable soap calculator, careful weighing technique, and a reasonable time to cure are the major things a person can use to ensure soap is safe. The zap test and/or testing the soap on your own skin at sink or shower are quick backup tests that help confirm safety. For a reliable final check, testing the alkalinity by titration would be a far better choice than relying on a pH test.
     
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  13. Jun 26, 2014 #13

    Bex1982

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    I think too, that you know when something went wrong, if it set up too fast, the fo seized the batch and you couldn't mix the lye in properly, it's brittle or just looks different than usual. If like the post above says, you use proper ingredients, formulations and lye calc, you shouldn't have a problem. The problem is things like leaving out an oil, weighing the lye wrong, new fo's messing things up, overheating etc. Once you've been making soap for a while you'll pick up on the signs that things are not right.
    If a batch looks good, i will zap test, cut n sniff (sometimes you can smell that there is still lye in the soap), look for anything like seeping oils, hard dry patches, yellow marbling. Then I'll do a lather test to make sure it actually is soap :)
    I usually ph tests my rebatches that are lye heavy, and phen works good for that. You're not looking for it to go clear mind you, all normal soap will turn the phen drops a shade of pink. It's that you don't want it to be the darkest shade of pink, the dark magenta. darkish-light pink are fine. Soap is usually between 8-11 ph. The deep magenta will indicate above 11 and then you can keep adding oil until the ph goes down. Again: BEBATCH ONLY. To tests, get some commercial soap make a solution see the shade of pink. Make some lye water, see the shade of pink. Then test some of your cured soap, see the shade of pink. Make some salt water, see the shade of pink. You can look online and see what the ph of these things are so that you know what the safe shade of pink looks like.
    People that say you can drop it on a dry soap bar are crazy! people that say it needs to be clear don't know what they're talking about. You need to make a proper solution, it only works in water. You don't have to add alcohol because if you bought the drops they are already in an alcohol solution.
    And to those saying ph testing costs a lot, I just wanted to say, you can get phen drop at amazon for less then $5 and you only use a drop to tests so that thing will last you forever!!
     
  14. Jun 26, 2014 #14

    Bex1982

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    Geez, I feel like you all were thinking that I only Ph test my soaps :-D haha, not the case.
    I said before why not do both? BOTH is what I said. If you check for zap and you look at the ph to use it as reference then what's the problem with that? It's good to know what to look for.
    Just because ph drops and whatnot don't work to to T on soap doesn't mean you can't get a round a bout idea of what's going on.
    I DO BOTH just for the record. Like I said I don't ph test EVERY soap either, these are batches that had big time problems which i rebabtched or that gave zap but looked fine.
    Ok, and I also did not say that zap testing is french kissing soap, i said that to be 100% sure your soap is safe you'd have to "french kiss" stick your tongue in all your soap searching for lye pockets. '
    Ok done :-D

    edit to say: essentially you are zap-testing the surface of your soap. what i meant is that you don't know everything that is going on IN the soap by surface testing. Ph tests won't tell you that either. What I stated from the beginning was that BOTH of them have their limitations. Can we just agree on that? There is no way, either of those tests will tell you for sure. Did you know that you can get zapped by one part in a bar but not by another? Only by the one lye heavy piece/pieces? That's why even more important than any of these tests, is LOOKING, FEELING, SMELLING, KNOWING your soap. Using your soap. Once you've done it long enough you will know when something went wrong.
     
    Last edited: Jun 26, 2014
  15. Jun 26, 2014 #15

    DeeAnna

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    Yep, you have some good thoughts there, Bex. Nicely said.
     
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  16. Jun 27, 2014 #16

    The Efficacious Gentleman

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    Aye, a good test rather than just a quick, no-thought-given test is best all round! Both pH testing as it is usually done by soapers and zap testing test a specific area on the surface. But only one of the methods tells you if that particular area on the surface is lye-heavy (unsafe) or not (safe) - and that is zap testing, not pH testing.

    But as you ask "why not both" I ask again - if pH testing doesn't tell if a soap is safe or not, why bother with it at all? What are people getting from the pH? Telling it to our customers/giftees? That is really just peddling the myth that the pH will be a deciding factor in whether or not it dries their skin and so on, a myth that Dove get's people fixated on ("It's pH 7, won't dry you out like soap does!"). If it's not for that, what are you getting out of the pH testing? A reference figure? But with the innacuracy of pH testing, I can easily imagine you could get a 0.5 variation on the rating even though the actual pH is the same, at the very least. That much innacuracy makes me think that it is a pretty poor reference - so again I ask what is the benefit of testing pH?

    By all means, test the pH - but I have yet to hear (or read) a reasonable case for doing so, in the form that soapers generally do it.
     
  17. Jun 27, 2014 #17

    DeeAnna

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    I think this is the point at which we should, once again, acknowledge "your mileage may vary" on this issue. I am going to take my own advice and gently move on....
     
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  18. Jun 27, 2014 #18

    Bex1982

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    yeah I don't really know. Either way, I mean if you guys say that lye can cure out anyway then I guess it's ok to just wait and keep zap testing it. I was just under the impression from a chemistry standpoint that saponification was done within 24-72 hours and after that your soap was safe to use and that curing was mainly for hardening of the soap. That longer cures are taught because older formulas called for a high amount of water and they didn't know the exact science behind the saponification process. That it's basically just been carried on that way. I don't care either way, actually I would like it to cure out and not have to rebatch lye heavy soaps.

    Edit to say: I wouldn't use ph as a selling point because CP soap would not test as neutral and that's what people want to hear. I was testing to just make sure it was under 11 and wouldn't irritate skin since that seems to be why most people won't buy handmade soap. I just wanted to make it better so I would get repeat customers at the farmers market.
     
    Last edited: Jun 27, 2014
  19. Jun 27, 2014 #19

    IrishLass

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    Yep- you'll hear that being touted, but I can't say that I necessarily agree 100% with it.

    I've had a few un-gelled batches of soap that still zapped for up to about 7 days after unmolding- much longer than 24 - 72 hours, which to me is living proof that time is not a very reliable indicator of doneness. After a few more days of cure, though, they happily tested out tongue-neutral. :)

    Dr. Kevin Dunn , in his book, 'Scientific Soapmaking' devotes 2 1/2 pages to the tongue test, which he supports as being a good, legitimate, time-honored method for testing for the presence of excess lye in soap. He states that a soap is not fully saponified until it is 'tongue-neutral' (his term), and encourages his readers to resist the temptation of attaching too much importance to results from pH strips.

    For those who want a concrete/precise number value of the total alkalinity, he provides detailed instructions on how to perform the Total Alkalinity test in chapter 15 of his book (the test that DeeAnna was talking about in one of her above posts). I'm glad he provides it, but hoo boy- it's way too involved for the likes of me! lol I do believe I'll just stick with the tongue test, thank you very much. lol

    For those interested, Dr. Dunn gives directions on how to conduct a tongue-test:

    Lick your finger, then rub your wet finger over the surface of the soap to be tested. Touch your soaped-up finger to the tip of your tongue. He says that completely saponified soap will taste fatty or soapy, while unsaponified soap will taste (in Dr. Dunn's own words), "like some-terrible-stinging-bitter-salty-something-that-you-would-prefer-never-to-taste-again. Bleaugh, splffft, hwauck, sptoo!" lol Then he goes on to tell you not to worry, just rinse your mouth out with water, and to remember that taste, because it's the taste of alkalai.

    As for belief that curing is mainly for hardening soap,....while I do agree that that is one of the purposes, I've learned through experience (as have many others as well) that there's much more going on inside the soap during cure than that, which for me, removes 'hardening' from being included under the 'mainly' heading. Instead, I consider hardening to be on equal footing with the incrementally increasing mildness and lathering abilities that my soap noticeably attains as the weeks go by, not to mention the increased longevity. They each are all equally important to me as being the reason for why I cure as far past the point of being tongue-neutral as I do. To me, soap is a lot like a fine wine or cheese- they get better in so many different ways with age.


    IrishLass :)
     
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  20. Jun 28, 2014 #20

    Bex1982

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    Usually when i do the wet finger thing the soap is fine, but..... A few times now I lick the soap, put kind of a lot of soap on there, it tastes ok, then 10 or so seconds later it starts to burn. Sometimes just a little burning but not much, sort of like if you licked salt. So is that lye heavy or do you only go by what you taste right off the bat? If I do the finger thing on the same soap it doesn't burn.
     

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