The Zap Test: A Visual Guide

Soapmaking Forum - Soap & Candle Forums

Help Support Soapmaking Forum - Soap & Candle Forums:

Joined
Aug 1, 2013
Messages
9,897
Reaction score
9,694
Location
Texas
pH measures the alkalinity of a substance. Soap is alkaline. You do not need to test it, I can tell you already.

What you need to know is if the soap is safe, meaning whether all the lye got used up saponifying the fat. Zap testing tells you if any lye is remaining. That tells you if it is safe.
 

DeeAnna

Well-Known Member
Joined
Feb 20, 2013
Messages
13,983
Reaction score
21,090
Location
USA
I'm throwing my vote in with Susie and The Gent. The pH will not tell you if there is excess lye; it will only tell you the pH. This is true for CP soap, HP soap, liquid soap, cream soap, shave soap, etc.

Every blend of fats (actually fatty acids) will make a soap that has a characteristic pH. Olive oil soap that has no excess lye will have a characteristic pH that is higher than, say, a coconut oil soap also with no excess lye. Which soap is lye heavy? Neither.

If you make a recipe over and over again the exact same way and with the exact same ingredients every time, the pH might be helpful as a general indicator, but that's a limited case. The pH test is often inaccurate the way most soapers do it, even people who shell out the big bucks for a nice pH meter. Strips, even the good ones, are usually off by a unit or two. And phenolpthalein drops ... well, don't get me started on them.

The zap test, which has been used by soap makers for centuries, and the modern standardized "free alkalinity" laboratory test are the best tests for excess lye in soap.

If you do your recipe calculations with care (or let a reputable calc do them for you), use at least some superfat, own a decent scale that weighs accurately, and have good working habits to prevent mis-measuring, you should seldom if ever get a zappy soap. That is especially true if you wait a couple-three days after the soap is unmolded before you zap test. If you are this kind of soaper, the zap test is simply a double check that all is well, not a horrible trial to endure.
 
Last edited:

ngian

Well-Known Member
Joined
Dec 9, 2014
Messages
567
Reaction score
467
Location
Athens, Greece (Very Hard Water)
And phenolpthalein drops ... well, don't get me started on them.

Hello DeeAnna, I'm quoting this old message of yours as I have lately investigated something that might change the way you think about phenolpthalein drops.

After reading Kevin Dunn's article at which he writes (when he describes how to make a lye excess soap on purpose):

When you open the cup the next day, the soap should appear normal, but if you have made it correctly it will be lye heavy. To see this, dribble a few drops of phenolphthalein indicator onto the soap. It should turn pink. Be aware that phenolphthalein is most often sold as a solution in alcohol, and this is what is needed for the test. A solution in water will turn pink whether or not the soap is lye heavy.
So if there is no water between phenolphthalein and NaOH then this indicator works well with the above test. I did the test my own where I had two cups, one with few NaOH pellets and the other with ammonium powder. Phenolphthalein turned pink on the NaOH pellets, so I guess someone that dislikes licking soaps while searching for excess lye spots on soaps, then this could be an alternative test.

I guess this might work well with the soap paste on a GLS soap too where there is not much water in it...

What do you all think about it? :)
 
Last edited:
Joined
Nov 19, 2013
Messages
9,230
Reaction score
9,795
Location
Austria
As she was talking about testing for pH, her comment still stands - it is not a good way of determining the pH of a soap.

As for use in general as a zap-alternative, while in that particular case it would show that the soap was lye heavy, I understand that it can also turn pink with non-lye heavy but high pH soaps, giving false positives
 

ngian

Well-Known Member
Joined
Dec 9, 2014
Messages
567
Reaction score
467
Location
Athens, Greece (Very Hard Water)
As she was talking about testing for pH, her comment still stands - it is not a good way of determining the pH of a soap.

I agree with you on that Gent...

As for use in general as a zap-alternative, while in that particular case it would show that the soap was lye heavy, I understand that it can also turn pink with non-lye heavy but high pH soaps, giving false positives


but I think that the specific phenolphthalein test might be an alternative to the Lick / Zap test, only if there is no water present at the test so as to see if there is really any NaOH excess. PH is only for aqueous solutions.
 
Joined
Aug 1, 2013
Messages
9,897
Reaction score
9,694
Location
Texas
The issue in question, ngian, is not what the pH of the soap is. The question is, "Is it safe?" The pH can be really high, but the soap can be safe.

Also, there are too many other factors that will turn phenolpthalein pink. Paper plates, paper towels, water, whatever was on the gloves that got that bit of soap out.... The list goes on and on. Since neither you nor I intend to go see how these folks perform that test, I deem it of little to no value in determining anything. There is simply no way to know whether it was performed correctly.

One simple, free, painless test that can be performed by anyone, anywhere with absolutely clear results is, to my mind, the better choice.

If someone is making liquid soap that they intend to sell, they need to know the pH to be able to add the preservative. They need to know how to properly dilute that soap paste and use a pH meter that is calibrated on a regular basis. This is the only time you need to know the pH. And this is the only proper way to determine it.
 
Last edited:

DeeAnna

Well-Known Member
Joined
Feb 20, 2013
Messages
13,983
Reaction score
21,090
Location
USA
Dunn is using the test as a "go - no go" test. He is checking this one single point -- Does the surface of this particular soap test alkaline to phenolphthalein or is it not? I agree a person can use phenolphthalein that way.

Note that Dunn is only using the test to confirm the pH on the surface is high for that particular soap in that particular experiment. The surface of other soaps may flush pink to phenolphthalein without actually being lye heavy overall -- but that's not the point of that particular experiment. He acknowledges this fact toward the end of the article you referenced when he discusses the question: "How does soda ash form on a normal soap, one that is not overly alkaline?..." So don't take his use of phenolphthalein in this experiment out of the context of the experiment.

Too many soapers use phenolphthalein outside the scope of Dunn's go-no go test without really understanding what they're doing. Some want to use phenolphthalein drops as a substitute for an excess alkalinity test or a zap test. Some liquid soap makers insist on cooking liquid soap paste until a dab of the paste tests colorless to phenolphthalein. Some believe the intensity of the indicator's color on bar soap or soap paste is directly correlated to a pH reading for the soap as a whole.

THAT is what I have a problem with -- how soapers use phenolphthalein in ways for which it is not suited or how they interpret the results in ways that are not realistic. I don't see any reason to change my point of view on this subject.

Edit: Dunn also says this: "...Sodium carbonate is a much weaker alkali than sodium hydroxide, and will not change the color of alcohol-based phenolphthalein indicator...." (Emphasis is mine.)

Sodium carbonate is indeed a weaker alkali, but what is more important to know about this statement is that sodium carbonate is only slightly soluble in alcohol. If a chemical does not dissolve (much or at all) in the alcohol of the phenolphthalein indicator, it's not going to make the alcohol solution alkaline and thus the chemical won't test pink to an alcohol-based phenolphthalein solution. If you put a drop of water on an ashy soap to dissolve the sodium carbonate and then test the wet spot with phenolphthalein, the phenolphthalein should turn pink. So it's important to also to not get the wrong impression of what Dunn is saying here -- in other words, don't take this statement out of context either.
 
Last edited:

LBussy

Well-Known Member
Joined
Jun 28, 2014
Messages
1,330
Reaction score
1,036
Location
Kansas City, MO
DeeAnna, when I read your posts I am often left saying out loud: "Damnit, that's what I was TRYING to say!" :)

Thanks for the clarity.
 

Margo

Well-Known Member
Joined
Jul 21, 2011
Messages
50
Reaction score
37
How disgusting! Non scientific methods of testing soap for lye is dangerous.
 

DeeAnna

Well-Known Member
Joined
Feb 20, 2013
Messages
13,983
Reaction score
21,090
Location
USA
"...How disgusting! Non scientific methods of testing soap for lye is dangerous...."

It's obvious you have a strong bias, but I have no idea what you're talking about. :think:
 
Last edited:
Joined
Nov 27, 2016
Messages
11
Reaction score
9
I've been zapped!



Greetings,

So...not a good way to start I know. But, I did the Zap test and sure enough I felt the sting, much like I do when I see George Clooney. My soap looks really pretty, I'm really shocked but I worry about it being unsafe to use. They have been curing for almost two weeks and I still got zapped. If I let them sit for 8 weeks and beyond (whatever it takes so long as I don't have to rebatch ...which I don't even know what that means. I certainly don't want to have to toss it or make laundry soap of it cause, well, I don't have a clue how to do that either. Any input from you sweet soapers would be greatly appreciated.[/SIZE]
 
Joined
Nov 19, 2013
Messages
9,230
Reaction score
9,795
Location
Austria


Greetings,

So...not a good way to start I know. But, I did the Zap test and sure enough I felt the sting, much like I do when I see George Clooney. My soap looks really pretty, I'm really shocked but I worry about it being unsafe to use. They have been curing for almost two weeks and I still got zapped. If I let them sit for 8 weeks and beyond (whatever it takes so long as I don't have to rebatch ...which I don't even know what that means. I certainly don't want to have to toss it or make laundry soap of it cause, well, I don't have a clue how to do that either. Any input from you sweet soapers would be greatly appreciated.[/SIZE]



Hi

Full recipe and process would be needed for any decent information. A photo would also be helpful. It might well be best to start a new thread instead
 
Joined
Aug 1, 2013
Messages
9,897
Reaction score
9,694
Location
Texas


Greetings,

So...not a good way to start I know. But, I did the Zap test and sure enough I felt the sting, much like I do when I see George Clooney. My soap looks really pretty, I'm really shocked but I worry about it being unsafe to use. They have been curing for almost two weeks and I still got zapped. If I let them sit for 8 weeks and beyond (whatever it takes so long as I don't have to rebatch ...which I don't even know what that means. I certainly don't want to have to toss it or make laundry soap of it cause, well, I don't have a clue how to do that either. Any input from you sweet soapers would be greatly appreciated.[/SIZE]

It would probably be best to start a new thread on this, but I will answer here.

The first thing we need to help you troubleshoot is the entire recipe in weights. Including the weight of the water and any additives, such as colorants and fragrance(s).

Oh, and welcome to the forum!
 

Margo

Well-Known Member
Joined
Jul 21, 2011
Messages
50
Reaction score
37
I would re-calculate your recipe using The Sage calculator.
 

Latest posts

Top