zap test - ya gotta do it

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Well-Known Member
Feb 7, 2016
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So Cal
silly me, this was the first time I was half-willing to zap test. No no, this was not my first zap test - far from it, I was just antsy because my Castile had swirls. So I was thinking not all had saponified properly and that I would get a bad zap. ... which no one likes... but ya gotta do it.

so I did... and passed
but the attached jpg is what my slices look like (unintentional ghosty swirl) - and you've heard my apprehension above. Next time I'm going to use a combination of lye.


Castile sliced 11-8-16.jpg
PH strips don't help much with soap since the ph soap is not neutral. If it's neutral it's not soap.

Ph strips can tell you the ph of the item - it doesn't just tell you if it is neutral.

So is this method of testing just not considered accurate for soaping?
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I play with ph strips - I like to see how close to 9ish I can get - that's my arbitrary sweet spot.
I think we all remember our first zap test. mine was a non event - no zap, but that was a kit with over 10% super fat.
don't get cocky - ya gotta do a proper zap test. I've felt the zing before. I didn't like it, but I keep doing it. Similar to washing the laundry - I don't like it, but I gotta keep doing it, because I want a nice product.

It is a pretty accident isn't it. I want to do that soapy ghosty swirl ... on purpose this time. And, in fact, I bought two bottles of Olive oil to try. I have a couple options to try for that swirl. I really like "auntie Clara's" methods (water amounts). I want to give that a try.
........So is this method of testing just not considered accurate for soaping?

It depends on who you ask!

But there are two issues - accuracy of the test and whether or not it is useful for soaping.

To get an industry standard reading you need to make a 1% solution and test that - just shoving a strip on a bar will give you "a" reading, but if you want to compare to other readings you would need to have apples and apples. The amount of water on the bar and how much soap has been dissolved on the surface when you touch a strip to it can all also affect the reading. Not to mention the interpretation of blue-green tones as to where on the scale it is.

So, is it useful? The biggest issue with soap is excess lye, with a pH test doesn't test for. Different soaping recipes have different pH levels by nature, so unless you have a baseline reading for your recipe the pH won't tell you if it is safe or not. And even then, is your different reading because of factors such as water amount on the soap or even different light levels affecting the way you read the colour.

The zap test tells you if the soap is safe. The recipe tells you how it will be to use. The pH tells you......the pH, which I don't need for soaping
Ditto what the good Gent said.

Yes, pH strips will give you a reading, but the question is this (as it relates to lye-based soap): how accurate is the reading from the strip, and what exactly does it mean for your soap?

Keep in mind that not all pH strips are equal when it comes to testing soap. The surfactant nature of soap is well known for messing with the chemical indicators on certain strips and giving false readings that can be off by as much as 2 or 3 points. The best strips to use with lye-based soap are the plastic lab-grade strips, specifically those that are made work to best within a higher pH range (i.e., 7 to 14). And like the good Gent said, you must make a 1% soap solution in order to get the most accurate reading. Macherey-Nagel makes such strips in case anyone is wondering (I bought mine from LotionCrafters).

Also keep in mind that fully-cured lye-based soap can have a wide range of pH but still be perfectly safe for use. For example, Johnson's Baby Soap with oatmeal has a pH of 12.35 and rates very low on the irritability index- lower than Zest Aqua soap and Camay Gala soap even though their pH's were lower (reference taken from 'Personal Cleanser Technology and Clinical Performance' article in the journal of Dermatological Therapy, 2004 pages 35-42).

I've tested my own soap (actually a 1% solution of my liquid soap paste that was zappy) with my plastic, lab-grade Macherey-Nagel strips and the pH showed 9.5. The zap soon went away over the next few hours as the paste finished fully saponifying, but the pH did not change much at all (rested between 9 and 9.5).

All of the above is why I (and many others here on the forum) choose to zap test instead of relying on pH when determining the safety of our soap. If the soap is tongue-neutral (notice I did not say pH neutral), it is safe to use. But if it zaps, it either needs more cure time, or else you may perhaps have a lye-heavy batch on your hands- the evidence for which is that the soap will still be zappy after 2 or three weeks of cure.

IrishLass :)

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